Electrifying Industrial Hydrogen Peroxide Production via Interfacial Molecular Mediation

Electrifying Industrial Hydrogen Peroxide Production via Interfacial Molecular Mediation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Electrifying Industrial Hydrogen Peroxide Production via Interfacial Molecular Mediation Michael Aziz, Dawei Xi, Yuheng Wu, Yuli Li, Richard Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4986886/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 22 Sep, 2025 Read the published version in Nature Chemistry → Version 1 posted You are reading this latest preprint version Abstract Hydrogen peroxide (H 2 O 2 ) is predominantly produced via the centralized thermocatalytic hydrogenation-anthraquinone oxidation (t-AO) process, a conventional nonaqueous method. Electrifying such nonaqueous processes with improved selectivity remains a significant challenge. Here, we present a multi-phase electrochemical anthraquinone autoxidation (e-AO) system that leverages an interfacial hydrogen atom transfer reaction facilitated by a heterogeneous molecular catalytic process. This design enables aqueous electrochemical reactions with over 97% efficiency at high current densities (> 200 mA cm −2 ), using only carbon electrodes. The aqueous-nonaqueous interfacial hydrogen atom transfer, operating with nearly 100% selectivity through a quinhydrone intermediate, eliminates waste caused by over-reduction of anthraquinones in conventional t-AO processes. Our approach combines the benefits of aqueous electrochemistry with those of the traditional t-AO process while addressing issues like unwanted electrolyte migration in aqueous systems and anthraquinone over-reduction in t-AO. This strategy enables the continuous production of low-cost, high-purity H 2 O 2 solutions (> 10 wt.%) and promotes the electrification and decentralization of nonaqueous chemical processes. Physical sciences/Chemistry/Electrochemistry Physical sciences/Chemistry/Chemical synthesis/Flow chemistry Physical sciences/Chemistry/Green chemistry/Sustainability Physical sciences/Chemistry/Organic chemistry/Synthetic chemistry methodology Physical sciences/Engineering/Chemical engineering Figures Figure 1 Figure 2 Figure 3 Figure 4 Highlights Using kinetically fast interfacial molecular mediation, we achieved a record high current density and efficiency of continuous electrochemical indirect H 2 O 2 synthesis (Fig. 4g), overcoming drawbacks of using noble metal or amphiphilic molecules. We obtained ~100% selectivity of aqueous-nonaqueous interfacial hydrogen atom transfer, overcoming the selectivity issue in incumbent and reported Pd hydrogenation methods. We systematically studied the thermodynamics and kinetics of the heterogenous interfacial molecular catalytic hydrogen atom transfer, enabling the electrification of other selective nonaqueous chemical processes due to the fast kinetics of interfacial reactions. The e-AO method has the feasibility of tuning and pairing molecular mediators in both the aqueous and nonaqueous phase. Main Hydrogen peroxide (H 2 O 2 ) is a strong, green oxidant with a wide variety of applications. At present, over 90% of industrial H 2 O 2 is manufactured through a thermocatalytic hydrogenation–anthraquinone oxidation (abbreviated as t-AO) sequence 1 . This batchwise and indirect synthesis involves three key steps (Fig. 1 a): 1. hydrogenation of non-aqueous-soluble anthraquinones (AQs) by grey H 2 from steam methane reforming (Eq. ( 1 )); 2. oxidation of the resulting reduced AQs by air, producing H 2 O 2 (Eq. ( 2 )); 3. extraction of H 2 O 2 by water. Because the nonaqueous solution and the AQs utilized are not soluble in water whereas H 2 O 2 has a low solubility in nonaqueous solutions, t-AO is capable of producing high concentration, high purity H 2 O 2 with high selectivity. The hydrogenation process to form the H 2 AQ, however, requires pressurized hydrogen input and palladium-based catalysts that can over-reduce AQs to unreactive compounds. Moreover, a considerable amount of energy and associated CO 2 emissions are associated with the production, distillation, and transport of H 2 O 2 . Therefore, electrochemical methods for decentralized H 2 O 2 production are highly desired. 2 $$\:{H}_{2}\left(methane-derived\right)+AQ\:\left(nonaq\right)\underrightarrow{Pd}{H}_{2}AQ\left(nonaq\right)$$ 1 $$\:{O}_{2}\left(air\right)+{H}_{2}AQ\left(nonaq\right)\to\:AQ\left(nonaq\right)+{H}_{2}{O}_{2}(nonaq,\:extracted\:by\:water)$$ 2 Recently, the on-site synthesis of H 2 O 2 has received significant attention 3, 4 , mostly focusing on development of catalysts 5–7 . However, aqueous electrolysis systems require ions as the charge carrier. If the system is not designed properly, impurities such as ions and additives in the electrolytes end up in the H 2 O 2 product, necessitating additional costly purification. 8, 9 With the goal of pure H 2 O 2 production, direct electrolysis methods utilizing gas diffusion electrode (GDE) engineering 10 , metal hydrides 11 , and the incorporation of solid electrolytes in multi-chamber cells 12, 13 have been reported. Although some studies have showcased impressively high current density and selectivity 14 , the direct electrolysis methods for H 2 O 2 production still face the challenge of producing high H 2 O 2 concentrations without experiencing severe declines in Faradaic efficiency. This occurs because increasing the H 2 O 2 concentration shifts the equilibrium of the oxygen reduction reactions (ORRs), suppressing the 2e – pathway to H 2 O 2 and promoting the competing 4e – pathway toward H 2 O 12 . Additionally, the direct synthesis of H 2 O 2 through the 2e − ORR relies on GDEs to facilitate O 2 mass transport, whereas GDEs are highly susceptible to performance failures caused by flooding 15, 16 . In contrast, indirect production of H 2 O 2 , which uses nonaqueous anthraquinone to mediate the 2e – ORR, exhibits minimal impact of product concentration on Faradaic efficiency, if electrified. Moreover, the replacing of the cathodic ORR with the electroreduction of flowable molecules mediating 2e − ORR eliminates the need for GDEs, allowing utilization of more robust electrodes. For electrifying indirect H 2 O 2 synthesis, researchers have examined phase transfer catalysis 17 , emulsions 18 and Pd membrane devices 19 to overcome the electrochemical limitations of nonaqueous solvents used for AO. Nevertheless, these reported H 2 O 2 synthesis methods still fall short of simultaneously meeting all critical target criteria: high concentration, high purity, high current density, high efficiency, scalability, and low cost. 20 Herein, we report an electrochemical hydrogenation – anthraquinone autoxidation (abbreviated as e-AO) with four separate steps (Fig. 1 b): 1. electrochemical hydrogenation; 2. aqueous-nonaqueous interfacial hydrogen atom transfer (ANIHAT); 3. anthraquinone oxidation (AO), producing H 2 O 2 ; and 4. H 2 O 2 extraction. Different redox-active AQs were used as the hydrogen-atom carriers in each of the two immiscible phases. We utilized 2,6-bis(3-phosphonopropyl-1-oxy)anthraquinone (DPPEAQ, aqueous AQ) 21 in the neutral pH aqueous phase (aq), and 2-ethylanthraquinone (EtAQ, nonaqueous AQ) in the nonaqueous phase (nonaq). Each AQ displays high solubility in its corresponding phase and poor solubility in the other, ensuring exceedingly low AQ loss rate by crossover into the other phase. During the operation, DPPEAQ is first reduced in an aqueous electrochemical cell (Equations ( 3 – 4 )). Then, H 2 DPPEAQ serves as a mediator, reducing EtAQ through ANIHAT (Eq. ( 5 )), a heterogeneous molecular catalytic process. $$\:Anode:\:\:{H}_{2}O\to\:{0.5O}_{2}+2{H}^{+}+2{e}^{-}$$ 3 $$\:Cathode:\:\:DPPEAQ\left(aq\right)+2{e}^{-}{+2{H}^{+}\to\:H}_{2}DPPEAQ\left(aq\right)$$ 4 $$\:{H}_{2}DPPEAQ\left(aq\right)+EtAQ\left(nonaq\right)\underleftrightarrow{interface}{DPPEAQ\left(aq\right)+H}_{2}EtAQ\left(nonaq\right)$$ 5 Afterward, the AO and H 2 O 2 extraction steps are carried out in the same manner as in t-AO processes. This method inherits the benefits from the t-AO process while avoiding its major drawbacks. The e-AO method decentralizes H 2 O 2 production powered by renewable electricity and circumvents the need for high pressure H 2 and the risk of AQ over-reduction. The ANIHAT process at the interface bridges the mass transport and thermodynamics of the aqueous and nonaqueous phase, transcending the challenges associated with electrochemical hydrogenation in the nonaqueous phase, even improving the selectivity of thermocatalytic hydrogenation during the t-AO. In addition, the facile reaction kinetics and high selectivity afforded by the ANIHAT process enable the e-AO method to stably produce H 2 O 2 under steady-state conditions at a high current density and with high efficiency. The nonaqueous phase also prevents the contamination of H 2 O 2 by the solutes in the electrolytes, avoiding the need for costly downstream purification processes. This dual-phase system demonstrates wide tunability of aqueous and nonaqueous redox molecules and organic solvents, providing ample space for further optimization and adaptation to other synthetic applications. Aqueous-nonaqueous interfacial hydrogen atom transfer (ANIHAT) Aqueous-soluble AQs have been developed for aqueous redox flow batteries and exhibit reversible, high efficiency, high current density electrochemical properties 22 . Yet solely using aqueous-soluble AQs for H 2 O 2 electrolysis is not sensible due to the coexistence of aqueous solutes in the H 2 O 2 product. In the e-AO process, the aqueous and nonaqueous AQs must remain exclusive within their respective phases to yield a pure aqueous solution of H 2 O 2 . Instead of using a typical non-aqueous solvent (a blend of heavy aromatic compounds and polar solvents) 23 in the t-AO process, we used a mixture of toluene and 1-decanol (Tol/Dec). This choice of solvent system facilitates characterization and allows for fine-tuning of polarity while maintaining excellent phase separation from water. Utilizing ultraviolet-visible spectrophotometry (UV-Vis), we ascertained that DPPEAQ is virtually insoluble in the nonaqueous phase and that EtAQ does not dissolve in water ( Supplementary Fig. S1 – S3, Table S1 ), prohibiting phase crossover of AQs. Consequently, redox processes between DPPEAQ and EtAQ are confined to the interface between the water and Tol/Dec. Using this system, we examined the kinetics and thermodynamics of the ANIHAT process – a spontaneous, non-Faradaic proton-coupled electron transfer process occurring at the aqueous-nonaqueous phase boundary. Given that the ANIHAT is a heterogeneous molecular catalytic process happening at the interface, free energies of the reaction products and intermediates can be influenced by the polarity of the nonaqueous solvents. The kinetics and thermodynamics of the ANIHAT process should be tunable via the solvent composition. To investigate the impact of nonaqueous solvent polarity on ANIHAT, kinetic experiments were conducted using the Tol/Dec solvent system with different volumetric ratios, using the abbreviated label n Tol/ m Dec to denote n mL toluene mixed with m mL 1-decanol. In each kinetic test, 10 mL 0.05 mol L − 1 H 2 DPPEAQ and 10 mL 0.05 mol L − 1 EtAQ were sequentially added into a 50 mL centrifuge tube inside a nitrogen-filled glovebox. Pumps were used to facilitate rapid mass transport in each phase, while maintaining a clear and stable aqueous-nonaqueous interface with an area of 6.2 cm 2 ( Supplementary Fig. S4 ). Intermittently, aliquots of the aqueous phase were collected for UV-Vis analysis. The temporal variations of the UV-Vis spectra of DPPEAQ/H 2 DPPEAQ in nonaqueous phases of different polarities are shown in Supplementary Fig. S5a – c . The absorbance at 355 nm were used to calculate the mole fractions of DPPEAQ and H 2 DPPEAQ ( Supplementary Fig. S6 ). Regressions of observed mole fractions as functions of time were conducted assuming ANIHAT as a reversible, second-order reaction (Equations 6 – 8 , Supplementary Fig. S7 ). The apparent rate constants for the forward reaction ( k 1 ) and for the reverse reaction ( k − 1 ) are displayed in Fig. 2 a – c . Here r represents the rate of the forward or backward reaction and A is the area of the aqueous-nonaqueous interface. $$\:{r}_{forward}=A{k}_{1}{[H}_{2}DPPEAQ\left]\right[EtAQ]$$ 6 $$\:{r}_{backward}=A{k}_{-1}\left[DPPEAQ\right]{[H}_{2}EtAQ]$$ 7 $$\:{K}_{eq}=\frac{{k}_{1}}{{k}_{-1}}$$ 8 As the volume fraction of 1-decanol, the more polar solvent, increased from 0.2 to 0.6, the equilibrium constant ( K eq ) increased from 0.03 to 0.29. Besides, k 1 increased as the volume fraction of 1-decanol rises, whereas k − 1 first declines and then remains steady. DFT calculations supported the hypothesized mechanism of ANIHAT. In the model, hydrogen atom transfer occurs through a quinhydrone-like intermediate formed on the aqueous-nonaqueous interface 24 . According to the computations, concerted proton-coupled electron transfer (PCET) is associated with a lower-energy transition state than is separated, sequential electron, proton transfer ( Supplementary Fig. S8 – S11 ) 25 . The quinhydrone intermediate allows fast PCET through the aqueous-nonaqueous interface 26 . For practical applications, vigorous agitation can substantially increase the interfacial area between the aqueous and nonaqueous phases, resulting in the attainment of charge equilibrium within only 3 s (Fig. 2 d, Supplementary Fig. S12 ). After sufficient agitation, we measured the charge capacity (in terms of electrons) leaving the aqueous phase (DPPEAQ donation) and the corresponding amount of capacity entering the nonaqueous phase (EtAQ reception). The efficiency of ANIHAT, defined as their ratio, was determined to be approximately 100% (Fig. 2 e). A trade-off exists with respect to the solvent polarity: a higher 1-decanol fraction would increase the kinetics of the forward reaction and thermodynamic driving force of ANIHAT but, by decreasing the solubility of EtAQ, it is detrimental to mass transport and concentration of the final H 2 O 2 product (Fig. 2 f). To balance these factors, we chose a 3Tol/2Dec as the nonaqueous solvent for further evaluation of the e-AO method in full system tests. HO production using the e-AO process Continuous H 2 O 2 production through the e-AO process was conducted in a tandem reactor, with three major components: aqueous electrochemistry (labeled as EChem) for aqueous AQ hydrogenation, ANIHAT for hydrogenation of the nonaqueous AQ, AO for highly selective 2 e oxygen reduction reaction and product extraction. In total, two aqueous phases (a solution of DPPEAQ and one containing the H 2 O 2 product) and one nonaqueous phase (EtAQ solution) were used and cycled individually. During ANIHAT and AO, which require interfacial reaction/extraction between the aqueous and nonaqueous phase, mixers and separators were used to facilitate the phase mixing and separation, as labeled in (Fig. 3 a, Supplementary Fig. S13 ). 17 To quantify the efficiency loss in each part, we first conducted a long-term cell cycling test of 0.1 mol L − 1 DPPEAQ in 0.33 mol L − 1 phosphate buffer (pH = 7) in order to maintain the pH of the electrolyte near neutral during operation. The cell was cycled against ferro/ferricyanide in a nitrogen-filled glovebox, to evaluate the efficiency of the EChem step. We used a standard constant-current followed by constant-voltage (CCCV) protocol accessing more than 95% of theoretical capacity of the DPPEAQ side. The cell was cycled for 6 days and demonstrated a Coulombic efficiency of approximately 99%, with a fade rate of approximately 0.2% day − 1 (Fig. 3 b). The fading was due to anthrone and dimer formation of DPPEAQ under near neutral conditions, 27 as we determined by liquid chromatography–mass spectrometry (LC-MS) analysis ( Supplementary Fig. S14 ). These side-products could be recovered through electro-oxidation 28 or chemical treatments 29 . To evaluate the compatibility of ANIHAT with EChem, after a few days cycling of only DPPEAQ in aqueous buffer, we added 3 mL of 0.1 mol L − 1 EtAQ in 3Tol/2Dec (theoretical capacity: 57.9 C) on top of the aqueous negolyte during cell cycling. The cell cycling capacity was found to increase from approximately 125 C to 180 C (Fig. 3 c), indicating that the nonaqueous EtAQ could be cycled along with the aqueous phase, presumably due to fast reversible ANIHAT and the similarity of redox potentials between the EtAQ and DPPEAQ. The initial drop of Coulombic efficiency in the first cycle was due to the presence of residual oxygen dissolved in the nonaqueous phase. A roughly constant Coulombic efficiency attained afterward indicates that ANIHAT was successfully incorporated into the EChem process (charging and discharging) with a high efficiency. Post-cycling LC-MS analysis provided evidence of the high selectivity of ANIHAT, showing only trace amounts of anthrone/dimer formation from EtAQ ( Supplementary Fig. S15 ). The pH of the DPPEAQ solution is crucial because a pH lower than 7 leads to DPPEAQ precipitation, whereas a pH higher than 12 causes deprotonation of H 2 EtAQ, forming a water-soluble anion, EtAQ 2− ( Supplementary Fig. S16 ) 30 . Having confirmed high efficiency of EChem and ANIHAT working in tandem, we next sought to include AO in a complete process for hydrogen peroxide synthesis. First, we used DPPEAQ to mediate the reduction of 50 mL of 0.5 mol L − 1 EtAQ in 3Tol/2Dec, which was added to the initially fully charged nonaqueous phase, and continued to charge the system until approximately 20% of EtAQ was reduced as H 2 AQ. At this point, the nonaqueous phase was agitated with air to completely oxidize H 2 EtAQ. Deionized water (DI water) in varying proportions to the nonaqueous phase was then used to extract the produced H 2 O 2 . The extraction was conducted twice. The concentration of H 2 O 2 products was determined by titration with KMnO 4 , from which the Faradaic efficiency (FE) was calculated based on the moles of obtained H 2 O 2 and the total moles of electrons injected into nonaqueous phase. The highest concentration of H 2 O 2 achieved in a single extraction trial was 3.2 mol L − 1 (> 10% wt.) at a water volumetric ratio of 0.015 to nonaqueous solvent (Fig. 3 d). The corresponding cumulative FE for two consecutive extractions was 75.7%, limited by the partition coefficient of H 2 O 2 between water and the nonaqueous solvent. 31 The FE of the whole process is about 85% when extraction efficiency is not limited, as verified by additional extraction. Finally, we performed continuous H 2 O 2 production in the tandem reactor. During the electrolysis at 50 mA cm − 2 in a 5 cm 2 flow cell, the cathode voltage remained stable ( Supplementary Fig. S17 – S18 ). The H 2 O 2 solution in the product tank was sampled intermittently and titrated by KMnO 4 to determine the concentration of product and FE. As expected, low FE was observed at the beginning due to capacity being injected into aqueous and nonaqueous AQs in order to build up the state of charge before reaching steady state. Subsequently, the steady-state FE of H 2 O 2 production was about 80%. The presence of residual oxygen in the nonaqueous phase after Separator 2 leading into Mixer 1 negatively influenced the FE ( Supplementary Fig. S19 – S20 ). During continuous production, the concentration of H 2 O 2 increased almost linearly with time, reaching 0.055 mol L − 1 (1.9% wt.) after 1000 s (Fig. 3 e). Generalization of the e-AO process The e-AO concept allows for flexible selection of anode reactions, as well as choice of aqueous AQs and nonaqueous quinones, providing space for further optimization and other applications. In principle, the anodic reaction of e-AO could be any oxidation reaction, provided the ion charge carriers into the cathode are protons. For example, we show that the hydrogen oxidation reaction (HOR) against a cation exchange membrane (CEM), 9 acidic oxygen evolution reaction (OER) against a CEM, 19 or alkaline OER against a bipolar membrane (BPM) can be used on the anode side 32 . These reactions, molecular candidates, and charge carriers are depicted in Fig. 4 a. During our tests, the cell was monitored with two voltmeters, one recording the full cell voltage (full cell voltage V 1 , positive), another connecting the working electrode and a reference electrode inserted in aqueous AQ catholyte (referenced V 2 ). V 2 was converted to cathode voltage vs. standard hydrogen electrode (SHE). The full cell polarization test was conducted using the negolytes of 0.1 mol L − 1 buffered DPPEAQ (pH = 7, 20% SOC) or 0.25 mol L − 1 1,8-dihydroxy-9,10-anthraquinone-2,7-disulphonic acid (DHAQDS, pH = 0, 20% SOC) against acidic HOR, acidic OER and alkaline OER 22 (Fig. 4 b). The cathode voltage was subtracted from the full cell voltage V 1 to gain insight into the properties of the counter reactions and cross-membrane resistance ( Supplementary Fig. S21 ). Notably, the cells working with an acidic catholyte delivered better polarization performance than those working with a pH-neutral catholyte, due to the elimination of the pH gradient and the reduction of ion polarization resistance across the membrane. For each kind of counter reaction, the HOR has the lowest energy cost but consumes hydrogen gas and, in our setup, utilizes a Pt/C gas diffusion electrode (GDE). The acidic OER with a CEM does not use hydrogen or a GDE, yet commonly requires noble-metal catalysts. 33 The alkaline OER with a BPM is a noble-metal-free alternative. The greater polarization resistance compared to acidic OER is attributable to the higher resistance of the BPM, indicating a need for further development of more effective BPMs. 34 The selection of aqueous AQs offered an opportunity for tuning the kinetics and thermodynamics during electrochemical hydrogenation and thus affecting the accessible current density and efficiency. We conducted measurements of the polarization performance of DPPEAQ and DHAQDS under different SOC and the corresponding Coulombic efficiency at low SOC (Fig. 4 c, 4 d). The Coulombic efficiency drop for DPPEAQ when the current density is greater in magnitude than 100 mA cm − 2 is caused by the pH gradient generated in the cell. Locally low pH on the near membrane side of the cathode under high current density boosts hydrogen evolution (HER) ( Supplementary Fig. S22 ). DHAQDS showed lower overpotential than DPPEAQ, delivering 400 mA cm − 2 at − 0.3 V vs SHE with 98.8% Coulombic efficiency. This is due to the uniform pH distribution in the acidic solution when using protons as charge carriers across the membrane. To show the practical feasibility of our method, we further tested the polarization of 2,2’-((9,10-dioxo-9,10-dihydroanthracene-2,6-diyl)bis(oxy))dipropionic acid (D2PEAQ) ( Supplementary Fig. S23 ), which is a considerably cheaper and synthetically accessible molecule, demonstrating higher solubility (0.5 mol L − 1 ) near neutral pH. 35 D2PEAQ also has a slightly more negative redox potential than DPPEAQ, which should facilitate the ANIHAT process, but at the expense of higher energy cost ( Supplementary Fig. S24 ). To examine the variation in spontaneity of ANIHAT among different aqueous and nonaqueous quinone pairs, the extent of reaction between three aqueous H 2 AQ and two nonaqueous quinones (EtAQ and naphthoquinone (NQ)) was measured (Fig. 4 e – f ). NQs are also commonly used in t-AO H 2 O 2 synthesis, but have a higher redox potential and a slower AO kinetics than AQs. 23, 36 The ANIHAT between H 2 D2PEAQ and NQ exhibited the highest thermodynamic spontaneity, even demonstrating promise for the utilization of low polarity organic solvents (toluene only). This suggests the potential to reduce organic solvent waste in the AO process, because higher polarity organic solvents can dissolve slightly in the H 2 O 2 product, and removal of that contamination requires a large amount of heavy aromatic solvent as extracting agent. 2 It is also worth noticing that the ANIHAT process occurs exclusively when there is compatibility between the hydrogen atom donor and acceptor. 37 When the aqueous AQ is instead replaced with a phenazine (2,2′-(phenazine-1,8-diyl)bis(ethane-1-sulfonate)), a viologen (methyl viologen), or vanadium (V 2+ ), in all cases paired with nonaqueous EtAQ, there was no significant charge transfer detected within a brief period although, according to the relevant redox potentials, the reaction is thermodynamically favored in all cases. Without formation of a suitable ANIHAT complex at the interface, such as a quinhydrone in the case of anthraquinone couples, 24 interfacial charge and proton transfers have a high energy barrier and slow kinetics. 38 Owing to the kinetics and selectivity of electrochemistry of aqueous AQs and ANIHAT, the e-AO method stands out due to its capability of producing H 2 O 2 with high concentration, high FE, and a high H 2 O 2 yield rate (Fig. 4 g). 10, 17, 19 Techno-economic analysis shows the potential of commercializing e-AO using green electricity, leading to an intriguing levelized cost of produced H 2 O 2 ( Supplementary Fig. S25 ). Flexibility of molecules and operating conditions are expected to lead to other applications and further optimization in the future. Outlook Achieving highly selective and efficient electrochemical reactions in nonaqueous phases remains a significant challenge. However, nonaqueous phases are often essential for specific reactions, offering advantages such as optimal solvent polarity or automatic phase separation from aqueous systems. In contrast, aqueous-phase electrochemistry is typically more cost-effective and efficient due to lower ionic resistance but often struggles with separating products from the aqueous electrolyte 39, 40 . We demonstrated a solution for this paradox by developing an electrified hydrogen peroxide production system. Through a comprehensive investigation of the mechanism and kinetic behavior of ANIHAT, we electrified the conventional t-AO process using aqueous electrochemistry. The e-AO process, with its flexibility in molecule, solvent, and anode choices, operates at high current densities with excellent Faradaic efficiency, yielding high-concentration, pure H 2 O 2 product. The process overcomes the selectivity and stability challenges of the incumbent t-AO process and enables the decentralized H 2 O 2 production. With future chemical and molecular engineering regarding nonaqueous solvents and ANIHAT redox pairs, the e-AO process has the potential to be scaled up, significantly diminishing organic waste and leading to better performance. The e-AO process can also facilitate the electrification of other applications that require peroxides, like the synthesis of alkyl oxides, selective oxidation of chemicals and water treatment. Furthermore, it has the potential to substitute H 2 O 2 for emissions-intensive feedstocks in the creation of new routes for process intensification of high-value chemicals 41 . More broadly, this work highlights the potential of integrating nonaqueous chemistry in organic phases with aqueous electrochemistry through interfacial chemical reactions. Unlike traditional phase-transfer catalysis, ANIHAT selectively transports only hydrogen atoms, rather than amphiphilic molecules, between phases. The formation of interfaces across which highly selective facile mass and energy transport occur should significantly benefit chemical synthesis processes by eliminating the requirement for further purification or separation 42–44 . With judicious selection of the chemical intermediates, the kinetics of the interfacial reaction can be sufficiently rapid 38, 45 for scalable applications using phases that are selective to the mass transport of certain species and feature automatic phase separation 40, 46 . Materials and methods Materials and synthesis. 2,6-Bis(3-phosphonopropyl-1-oxy)anthraquinone (DPPEAQ) was purchased from TCI Chemicals 21 . Nafion® 212 as cation exchange membrane and Fumasep® FBM as bipolar membrane were purchased and only soaked in DI water before usage. Ir/C, Ni foam, hydrophobic carbon paper, 5 mg cm − 2 Pt gas diffusion electrode (GDE) were purchased from fuel cell store. Potassium permanganate (KMnO 4 ), sodium oxalate (Na 2 C 2 O 4 ), dipotassium phosphate (K 2 HPO 4 ), monopotassium phosphate (KH 2 PO 4 ), sulfuric acid (H 2 SO 4 ), potassium hydroxide (KOH), potassium ferricyanide (K 3 Fe(CN) 6 ), potassium ferrocyanide (K 4 Fe(CN) 6 ). 2-ethylanthraquinone (EtAQ), naphthoquinone (NQ), 2,6-dihydroxyl-9,10-anthraquinone (DHAQ) and 1,8-dihydroxy-9,10-anthraquinone-2,7-disulphonic acid, sodium salt were purchased from Sigma-Aldrich. 1,8-dihydroxy-9,10-anthraquinone-2,7-disulphonic acid (DHAQDS) was prepared using a cation exchange resin column filled with Amberlyst® 15(H) to exchange sodium ions into protons 22 . 2,2’-((9,10-dioxo-9,10-dihydroanthracene-2,6-diyl)bis(oxy))dipropionic acid (D 2 PEAQ) was synthesized according to our previous report. 35 Electrode preparation. Electrodes for aqueous electrolyte tests are carbon papers (SGL 39AA) baked at 400°C overnight. Carbon paper loaded with about 1 mg cm − 2 Ir/C was served for acidic OER. Typically, 10 mg of Ir/C catalysts, 0.97 mL of 2-propanol and 30 µL of Nafion binder solution were mixed to form a catalyst ink. The ink was sonicated for about 30 min and then spray coated on carbon paper. Ni foam loaded with NiFe hydroxides was served for alkaline OER. The electrode was prepared by electrodeposition washed 2 ·6H 2 O (0.1 mol L − 1 ) and FeSO 4 ·7H 2 O (0.05 mol L − 1 ) under − 10 mA cm − 2 for 1 min, and was washed with DI water. H 2 O 2 detection. The concentration of H 2 O 2 was detected by a standard KMnO 4 titration process. KMnO 4 solution was prepared by dissolving 7.9 g KMnO 4 in 1 L of 1 N H 2 SO 4 (about 0.05 mol L − 1 KMnO 4 , 0.5 mol L − 1 H 2 SO 4 ), then was boiled and stored in brown reagent bottles in the dark. The exact concentration of KMnO 4 was calibrated by titrating with a standard Na 2 C 2 O 4 solution at about 70°C. Analytical concentration and SOC detection. The analytical concentration and state of charge (SOC) of DPPEAQ were measured by UV-Vis spectrophotometry. We defined the analytical concentration (c A ) as the total concentration of DPPEAQ and H 2 DPPEAQ, and the SOC as the concentration of H 2 DPPEAQ divided by c A . In each test, the electrolyte sample was collected and diluted to the detection range with 1 mol L − 1 KOH in a nitrogen filled glove box. The KOH was purged with N 2 for 15 min to get rid of the residual O 2 in advance. The absorbance within the wavelength range of 200 nm to 800 nm were then recorded by UV-Vis spectrophotometry (Agilent Cary 60 spectrometer). The absorbance at the wavelengths of 355 nm and 408 nm were ascribed to DPPEAQ (SOC = 0%) and H 2 DPPEAQ (SOC = 100%), respectively. By varying c A , we calibrated the concentration-absorbance curves. The concentration-absorbance curves of EtAQ was calibrated following the same procedures. We obtained DPPEAQ solutions with a series of SOCs by mixing 0.05 mol L − 1 DPPEAQ and 0.05 mol L − 1 H 2 DPPEAQ in varying proportions. The absorbance at the wavelength of 355 nm (A 355 ) exbibits a strong linear relationship with SOC. Therefore, at a specific c A , the SOC could be calculated as Equation S1: $$\:x=\frac{{A}_{355,SOC=0}-{A}_{355,SOC=x}}{{A}_{355,SOC=0}-{A}_{355,SOC=1}}$$ S1 x is the SOC to be determined. Solubility test. The solubility of DPPEAQ, D 2 PEAQ, and EtAQ was measured by adding each compound into the corresponding solutions under sonication until no further solids could be dissolved. The saturated solution was then diluted, and its concentration was determined by UV-Vis spectrophotometry. The concentration was calculated according to a pre-calibrated absorbance-concentration curve. In addition, the solubility of DPPEAQ in the nonaqueous phase and that of EtAQ in the aqueous phase were measured following the same procedure without the dilution step. ANIHAT kinetics measurement. The kinetic rate constants involved in ANIHAT were measured using several nonaqueous phase polarities in a nitrogen glovebox. The aqueous phase consisted of a solution containing 0.05 mol L − 1 of DPPEAQ dissolved in 0.33 mol L − 1 phosphate buffer with a pH of 7, which we call buffered DPPEAQ. The nonaqueous phase was 0.05 mol L − 1 EtAQ dissolved in nTol/mDec. Both the aqueous and nonaqueous phases were purged of dissolved O 2 with nitrogen prior to being transferred into the glovebox. DPPEAQ was first charged to a SOC of 100% under a CCCV protocol against buffered ferro/ferricyanide. The cutoff voltage for 20 mA cm − 2 constant current was set as 1.2 V, and the voltage was held until the current density dropped in magnitude to below 0.2 mA cm − 2 . Then, 20 mL of DPPEAQ were transferred to a 50 mL centrifuge tube and 20 mL of EtAQ was added onto the top of H 2 DPPEAQ carefully without mixing or splashing. The aqueous-nonaqueous interfacial area was 6.2 cm 2 . The meantime, two KNF pumps consistently circulated the aqueous and nonaqueous phase respectively at 20 mL min − 1 while not disrupting the interface between them. A timer was started when nonaqueous solution was added. At regular intervals, 0.5 mL of aqueous and nonaqueous samples were taken out from each phase and diluted using 1 mol L − 1 KOH by a factor of 500 for UV-Vis analysis, until the SOC of DPPEAQ reached equilibrium. Based on a reversible second-order kinetic model, the apparent kinetic constants were derived. The kinetics test of ANIHAT under vigorous stirring was performed in the N 2 glovebox. In a mixer, after 3 seconds of vigorous stirring and standing still until clear phase separation, 0.5 mL aqueous phase were taken out and diluted for UV-Vis. ANIHAT test for various redox couples . The efficiency of ANIHAT and the spontaneity of ANIHAT with different combinations of aqueous anthraquinones (DPPEAQ, D2PEAQ, DHAQDS) and nonaqueous quinones (EtAQ, naphthoquinone) in toluene or 3Tol/2Dec were conducted by measuring the extent of reaction between 0.05 mol L − 1 aqueous H 2 AQ and 0.05 mol L − 1 nonaqueous quinones in the N 2 glovebox. First, 5 mL aqueous AQ solutions were charged to 100% SOC with CCCV protocol. The recorded capacity was regarded as the overall capacity. Next, 5 mL nonaqueous quinone solution was added to the aqueous phase. After a sufficient amount of stirring, the emulsion was allowed to settle until it separated into two distinct phases. Recharging the separated aqueous solution using the same CCCV protocol allowed for the determination of the charge transferred throughout the ANIHAT procedure. The extent of reaction was determined by dividing the transferred charge by the total charge. UV-Vis spectrophotometry was used to cross confirm the state of charge of aqueous AQs before and after ANIHAT. Cycling of DPPEAQ. The cycling test of DPPEAQ was conducted by employing the constant current followed by constant voltage (CCCV) protocol. A cell composed of 10 mL 0.1 mol L − 1 buffered DPPEAQ paired with 100 mL of 0.08 mol L − 1 ferrocyanide + 0.02 mol L − 1 ferricyanide. Excess capacity in the posolyte ensured that DPPEAQ was the capacity limiting side of the cell. The two half-cells were separated by a Nafion 212 membrane. Two layers of carbon paper were used in each half-cell. The flow rate of electrolytes was set to be 60 mL min − 1 . The cell was cycled at a constant current of 20 mA cm − 2 , followed by a constant charging voltage of 1.2 V and discharging voltage of 0.3 V until the current drops to 0.2 mA cm − 2 . The cycling test of DPPEAQ + EtAQ was conducted using the same protocol. DPPEAQ initially underwent 32 consecutive cycles, followed by the addition of 3 mL of 0.1 mol L − 1 EtAQ in 3Tol/2Dec on top of it. Subsequently, an additional 5 cycles were conducted. Performance test of H 2 O 2 production. The production of high concentration H 2 O 2 was conducted batchwise. 10 mL 0.1 mol L − 1 buffered DPPEAQ and 50 mL 0.5 mol L − 1 EtAQ in 3Tol/2Dec was charged against acidic OER. While charging, N 2 gas was continuously purged above the solution to prevent the oxidation of H 2 EtAQ by O 2 . As the SOC of EtAQ went higher, the color of nonaqueous phase turned dark green. After the SOC of EtAQ reached approximately 20%, the charging was stopped and the DPPEAQ solution was removed from the nonaqueous phase. Next, the nonaqueous phase was exposed to air for oxidation. DI water in varying proportion to the nonaqueous phase was then added to extract the produced H 2 O 2 . The extraction was conducted twice. The concentration of generated H 2 O 2 was titrated by KMnO 4 . The continuous H 2 O 2 production was conducted in the tandem reactor 17 . Specifically, 18 mL DPPEAQ (0.1 mol L − 1 DPPEAQ in 0.33 mol L − 1 phosphate pH 7 buffer) and 18 mL pure water were stored in the catholyte tank and the product tank, respectively, and continuously pumped through the corresponding mixers and separators. 30 mL 0.25 mol L − 1 EtAQ phase was then added and circulated on the top of them. The flow rate was about 20 mL min − 1 . When a negative potential was applied to the cathode, DPPEAQ was hydrogenated and transported to Mixer 1 (Fig. 3 a). In Mixer 1, the DPPEAQ phase mixed with the EtAQ phase under vigorous stirring, ensuring the ANIHAT was conducted thoroughly. Subsequently, the EtAQ phase carrying H 2 EtAQ was transported to Mixer 2, mixing with air and the H 2 O phase. The generated H 2 O 2 accumulated in the product tank, and the oxidized EtAQ was circulated back to Mixer 1, moving on to the next reaction round. The mass flow of air was controlled to minimize oxygen residue in the non-aqueous phase to avoid the unwanted oxidation of the reduced DPPEAQ. Within the continuous production of H 2 O 2 , a current of 250 mA was employed, with a corresponding area of 5 cm 2 . During the electrolysis, the cathode potential was recorded using a voltmeter connected to the cathode and a reference electrode inserted in the catholyte. Every 200 s, 0.5 mL of the aqueous phase was taken out from the H 2 O 2 collection tank for H 2 O 2 detection. Before and after the electrolysis, electrochemical impedance spectroscopy (EIS) measurements were conducted with 10 mV perturbation and with frequency ranging from 1 to 100000 Hz to determine the high-frequency area-specific resistance (ASR). Polarization test . The full cell polarization test was conducted with different combinations of anode reactions, membranes, and cathode pH. The potential was swept from open circuit voltage at a scan rate of 100 mV s − 1 using linear sweep voltammetry (LSV) controlled through the full cell voltage V 1 , and the resulting current response was measured. During tests, the cell was monitored with two voltmeters, one recording the full cell voltage (V 1 ) and another recording the cathode potential (V 2 ). The corresponding current was recorded. The polarization performance of the cathode was evaluated using 0.1 mol L − 1 buffered DPPEAQ, 0.25 mol L − 1 buffered D2PEAQ and 0.25 mol L − 1 DHAQDS in 0.5 mol L − 1 H 2 SO 4 . The cell was first charged to certain SOCs with respect to theoretical capacity. Then, LSV was conducted through sweeping the full cell voltage V 1 at a scan rate of 100 mV s − 1 , with half-cell voltage V 2 measured using a reference electrode inserted in the catholyte. The half-cell LSV and OCV results (converted to vs. SHE) were determined based on V 2 and the corresponding current density. Quantum Chemistry computations. Detailed computational methods, which include all meta data and formula development, are described in the Supplementary Information. Generally, the geometry optimization of the quinhydrone analog intermediate was conducted based on density functional theory calculations (DFT), as performed using the Vienna ab initio simulation package (VASP). The calculation of the potential energy surface of ANIHAT was accomplished using Gaussian 16 package. Declarations Data availability : All data are available in the manuscript or the supplementary materials. Acknowledgments: This research was supported by Harvard Climate Change Solutions Fund, Harvard Dean's Competitive Fund and by the Harvard School of Engineering and Applied Sciences. Authors Contributions Statement : D.X. conceived the idea. D.X. and Y.W. designed and conducted hardware design, tests and electrochemical experiments. Y.L. did the DFT calculation. R.Y.L. supervised the reaction mechanism study. M.J.A. supervised the project. D.X., Y.W. and M.J.A. drafted the manuscript. All authors edited the manuscript. Competing Interests Statement : A patent application has been filed for this work. References Hess, W. T., Hydrogen Peroxide. In Kirk-Othmer Encyclopedia of Chemical Technology , 2000. Campos‐Martin, J. M.; Blanco‐Brieva, G.; Fierro, J. L., Hydrogen peroxide synthesis: an outlook beyond the anthraquinone process. Angewandte Chemie International Edition 2006, 45 (42), 6962-6984. Perry, S. C.; Pangotra, D.; Vieira, L.; Csepei, L.-I.; Sieber, V.; Wang, L.; Ponce de León, C.; Walsh, F. C., Electrochemical synthesis of hydrogen peroxide from water and oxygen. Nat. Rev. Chem. 2019, 3 (7), 442-458. Edwards, J. K.; Solsona, B.; N, E. N.; Carley, A. F.; Herzing, A. A.; Kiely, C. J.; Hutchings, G. J., Switching off hydrogen peroxide hydrogenation in the direct synthesis process. Science 2009, 323 (5917), 1037-1041. Siahrostami, S.; Verdaguer-Casadevall, A.; Karamad, M.; Deiana, D.; Malacrida, P.; Wickman, B.; Escudero-Escribano, M.; Paoli, E. A.; Frydendal, R.; Hansen, T. W.; Chorkendorff, I.; Stephens, I. E.; Rossmeisl, J., Enabling direct H2O2 production through rational electrocatalyst design. Nat. Mater. 2013, 12 (12), 1137-43. Zhu, Q.; Hinkle, M.; Kim, D. J.; Kim, J.-H., Modular hydrogen peroxide electrosynthesis cell with anthraquinone-modified polyaniline electrocatalyst. ACS ES&T Engineering 2020, 1 (3), 446-455. Freakley, S. J.; He, Q.; Harrhy, J. H.; Lu, L.; Crole, D. A.; Morgan, D. J.; Ntainjua, E. N.; Edwards, J. K.; Carley, A. F.; Borisevich, A. Y.; Hutchings, G. J., Palladium-tin catalysts for the direct synthesis of H2O2 with high selectivity. Science 2016, 351 (6276), 965-968. Zhang, X.; Xia, Y.; Xia, C.; Wang, Haotian., Insights into practical-scale electrochemical H2O2 synthesis. Trends in Chemistry 2020, 2 (10), 942-953. Yamanaka, I.; Onizawa, T.; Takenaka, S.; Otsuka, K., Direct and continuous production of hydrogen peroxide with 93% selectivity using a fuel‐cell system. Angew. Chem. 2003, 115 (31), 3781-3783. Yamanaka, I.; Murayama, T., Neutral H2O2 synthesis by electrolysis of water and O2. Angew. Chem. 2008, 120 (10), 1926-1928. Huang, A.; Delima, R. S.; Kim, Y.; Lees, E. W.; Parlane, F. G.; Dvorak, D. J.; Rooney, M. B.; Jansonius, R. P.; Fink, A. G.; Zhang, Z.; Berlinguette, Curtis. P., Direct H2O2 synthesis, without H2 gas. J. Am. Chem. Soc. 2022, 144 (32), 14548-14554. Xia, C.; Xia, Y.; Zhu, P.; Fan, L.; Wang, Haotian., Direct electrosynthesis of pure aqueous H2O2 solutions up to 20% by weight using a solid electrolyte. Science 2019, 366 (6462), 226-231. Zhang, X.; Zhao, X.; Zhu, P.; Adler, Z.; Wu, Z.-Y.; Liu, Y.; Wang, Haotian., Electrochemical oxygen reduction to hydrogen peroxide at practical rates in strong acidic media. Nat. Commun. 2022, 13 (1), 2880. Xia, Y.; Zhao, X.; Xia, C.; Wu, Z.-Y.; Zhu, P.; Kim, J. Y.; Bai, X.; Gao, G.; Hu, Y.; Zhong, J.; Wang, Haotian., Highly active and selective oxygen reduction to H2O2 on boron-doped carbon for high production rates. Nat. Commun. 2021, 12 (1), 4225. Preger, Y.; Gerken, J. B.; Biswas, S.; Anson, C. W.; Johnson, M. R.; Root, T. W.; Stahl, S. S., Quinone-mediated electrochemical O2 reduction accessing high power density with an off-electrode Co-N/C catalyst. Joule 2018, 2 (12), 2722-2731. Twilton, J.; Johnson, M. R.; Sidana, V.; Franke, M. C.; Bottecchia, C.; Lehnherr, D.; Lévesque, F.; Knapp, S. M.; Wang, L.; Gerken, J. B.; Stahl, S. S., Quinone-mediated hydrogen anode for non-aqueous reductive electrosynthesis. Nature 2023, 623 (7985), 71-76. Murray, A. T.; Voskian, S.; Schreier, M.; Hatton, T. A.; Surendranath, Yogesh., Electrosynthesis of hydrogen peroxide by phase-transfer catalysis. Joule 2019, 3 (12), 2942-2954. Huissoud, A.; Tissot, P., Electrochemical reduction of 2-ethyl-9, 10-anthraquinone (EAQ) and mediated formation of hydrogen peroxide in a two-phase medium Part II: Production of alkaline hydrogen peroxide by the intermediate electroreduction of EAQ in a flow-by porous electrode in two-phase liquid–liquid flow. J. Appl. Electrochem. 1999, 29 , 17-25. Fink, A. G.; Delima, R. S.; Rousseau, A. R.; Hunt, C.; LeSage, N. E.; Huang, A.; Stolar, M.; Berlinguette, Curtis. P., Indirect H2O2 synthesis without H2. Nat. Commun. 2024, 15 (1), 766. Tang, J.; Zhao, T.; Solanki, D.; Miao, X.; Zhou, W.; Hu, Shu., Selective hydrogen peroxide conversion tailored by surface, interface, and device engineering. Joule 2021, 5 (6), 1432-1461. Ji, Y.; Goulet, M. A.; Pollack, D. A.; Kwabi, D. G.; Jin, S.; Porcellinis, D.; Kerr, E. F.; Gordon, R. G.; Aziz, M. J., A Phosphonate‐Functionalized Quinone Redox Flow Battery at Near‐Neutral pH with Record Capacity Retention Rate. Adv. Energy Mater. 2019, 9 (12). Huskinson, B.; Marshak, M. P.; Suh, C.; Er, S.; Gerhardt, M. R.; Galvin, C. J.; Chen, X.; Aspuru-Guzik, A.; Gordon, R. G.; Aziz, M. J., A metal-free organic-inorganic aqueous flow battery. Nature 2014, 505 (7482), 195-8. Fajt, V.; Kurc, L.; Červený, L., The effect of solvents on the rate of catalytic hydrogenation of 6‐ethyl‐1,2,3,4‐tetrahydroanthracene‐9,10‐dione. Int. J. Chem. Kinet. 2008, 40 (5), 240-252. Patil, A.; Curtin, D.; Paul, I., Interconversion by hydrogen transfer of unsymmetrically substituted quinhydrones in the solid state. Crystal structure of the 1: 2 complex of 2, 5-dimethylquinone with hydroquinone. J. Am. Chem. Soc. 1984, 106 (14), 4010-4015. Mercado, F. V.; Fernández, R. A.; Iglesias, R. A.; Dassie, S. A., Facilitated proton transfer reactions via water autoprotolysis across oil| water interfaces. Spectroelectrochemical analysis. Electrochim. Acta 2019, 299 , 430-440. Patil, A.; Curtin, D.; Paul, I., Solid-state formation of quinhydrones from their components. Use of solid-solid reactions to prepare compounds not accessible from solution. J. Am. Chem. Soc. 1984, 106 (2), 348-353. Goulet, M. A.; Tong, L.; Pollack, D. A.; Tabor, D. P.; Odom, S. A.; Aspuru-Guzik, A.; Kwan, E. E.; Gordon, R. G.; Aziz, M. J., Extending the Lifetime of Organic Flow Batteries via Redox State Management. J. Am. Chem. Soc. 2019, 141 (20), 8014-8019. Jing, Y.; Zhao, E. W.; Goulet, M. A.; Bahari, M.; Fell, E. M.; Jin, S.; Davoodi, A.; Jonsson, E.; Wu, M.; Grey, C. P.; Gordon, R. G.; Aziz, M. J., In situ electrochemical recomposition of decomposed redox-active species in aqueous organic flow batteries. Nat. Chem. 2022, 14 (10), 1103-1109. Shang, H.; Zhou, H.; Zhang, W.; Zhang, K., Regeneration of working solution in the hydrogen peroxide production process. The Canadian Journal of Chemical Engineering 2011, 89 (5), 1296-1302. Kwabi, D. G.; Lin, K.; Ji, Y.; Kerr, E. F.; Goulet, M.-A.; De Porcellinis, D.; Tabor, D. P.; Pollack, D. A.; Aspuru-Guzik, A.; Gordon, R. G.; Aziz, M. J., Alkaline Quinone Flow Battery with Long Lifetime at pH 12. Joule 2018, 2 (9), 1894-1906. Lu, S.; Wang, L.; Wang, Y.; Mi, Z., Kinetic Model of Gas‐Liquid‐Liquid Reactive Extraction for Production of Hydrogen Peroxide. Chem. Eng. Technol. 2011, 34 (5), 823-830. Li, T.; Lees, E. W.; Goldman, M.; Salvatore, D. A.; Weekes, D. M.; Berlinguette, C. P., Electrolytic conversion of bicarbonate into CO in a flow cell. Joule 2019, 3 (6), 1487-1497. Wu, Z.-Y.; Chen, F.-Y.; Li, B.; Yu, S.-W.; Finfrock, Y. Z.; Meira, D. M.; Yan, Q.-Q.; Zhu, P.; Chen, M.-X.; Song, T.-W., Non-iridium-based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane water electrolysis. Nat. Mater. 2023, 22 (1), 100-108. Oener, S. Z.; Foster, M. J.; Boettcher, S. W., Accelerating water dissociation in bipolar membranes and for electrocatalysis. Science 2020, 369 (6507), 1099-1103. Kerr, E. F.; Tang, Z.; George, T. Y.; Jin, S.; Fell, E. M.; Amini, K.; Jing, Y.; Wu, M.; Gordon, R. G.; Aziz, M. J., High energy density aqueous flow battery utilizing extremely stable, branching-induced high-solubility anthraquinone near neutral pH. ACS Energy Lett. 2022, 8 (1), 600-607. Kurc, L.; Páter, M.; Červený, L., Activity of basic catalysts in oxidation of 2-ethyl-5,6,7,8-tetrahydro-9,10-anthrahydroquinone. J. Mol. Catal. A: Chem. 2003, 202 (1-2), 327-332. Osakai, T.; Okamoto, M.; Sugihara, T.; Nakatani, K., Bimolecular-reaction effect on the rate constant of electron transfer at the oil/water interface as studied by scanning electrochemical microscopy. J. Electroanal. Chem. 2009, 628 (1-2), 27-34. Cukier, R. I.; Nocera, Daniel. G., Proton-coupled electron transfer. Annu. Rev. Phys. Chem. 1998, 49 (1), 337-369. Xia, C.; Zhu, P.; Jiang, Q.; Pan, Y.; Liang, W.; Stavitski, E.; Alshareef, H. N.; Wang, Haotian., Continuous production of pure liquid fuel solutions via electrocatalytic CO2 reduction using solid-electrolyte devices. Nat. Energy 2019, 4 (9), 776-785. Sherbo, R. S.; Delima, R. S.; Chiykowski, V. A.; MacLeod, B. P.; Berlinguette, C. P., Complete electron economy by pairing electrolysis with hydrogenation. Nat. Catal. 2018, 1 (7), 501-507. Lewis, R. J.; Hutchings, G. J., Selective oxidation using In situ-generated hydrogen peroxide. Acc. Chem. Res. 2023, 57 (1), 106-119. Chanda, A.; Fokin, V. V., Organic synthesis “on water”. Chem. Rev. 2009, 109 (2), 725-748. Shang, H.; Chen, Y.; Guan, S.; Wang, Y.; Cao, J.; Wang, X.; Li, H.; Bian, Z., Scalable and selective gold recovery from end-of-life electronics. Nature Chemical Engineering 2024, 1 (2), 170-179. Xu, Y.; Mao, Z.; Qu, R.; Wang, J.; Yu, J.; Luo, X.; Shi, M.; Mao, X.; Ding, J.; Liu, B., Electrochemical hydrogenation of oxidized contaminants for water purification without supporting electrolyte. Nature Water 2023, 1 (1), 95-103. Willner, I., Photoinduced electron transfer across a water-oil boundary: A model for redox reaction separation. 1979 . Han, C.; Zenner, J.; Johny, J.; Kaeffer, N.; Bordet, A.; Leitner, W., Electrocatalytic hydrogenation of alkenes with Pd/carbon nanotubes at an oil–water interface. Nat. Catal. 2022, 5 (12), 1110-1119. Additional Declarations Yes there is potential Competing Interest. A patent related to the technique included in this manuscript has been submitted. Supplementary Files image1.png TOC: ElectrifyingindustrialH2O2productionSI.docx Cite Share Download PDF Status: Published Journal Publication published 22 Sep, 2025 Read the published version in Nature Chemistry → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4986886","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":352761258,"identity":"bb745ebe-9dad-458f-b6b1-d86fa43d5aee","order_by":0,"name":"Michael Aziz","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwUlEQVRIiWNgGAWjYJCCAwwVByAsHgYGxgbitJwhVQsDYxspWnTbjz88+HPeHXnzGcnPPrxhsJHdcICAFrMzCQkHJLc9M5xzI8145hyGNGPCWg4kHDhguO0w4wyeA8bMPAyHEwlrOf+w4UDinMP2M3iOfwZq+U+ElhvJDAcONhxOnMHeA7LlADFanjEcbDh2OBmopZhxjkGy8UzCDkt//PFHzWHbGczsmxneVNjJ9hHSggYMSFM+CkbBKBgFowAHAADVnEvECVTnBQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-9657-9456","institution":"Harvard University","correspondingAuthor":true,"prefix":"","firstName":"Michael","middleName":"","lastName":"Aziz","suffix":""},{"id":352761259,"identity":"b2a4d8f1-92f3-4d61-8fe5-556c0376becd","order_by":1,"name":"Dawei Xi","email":"","orcid":"https://orcid.org/0000-0002-5412-3474","institution":"Harvard University","correspondingAuthor":false,"prefix":"","firstName":"Dawei","middleName":"","lastName":"Xi","suffix":""},{"id":352761260,"identity":"a06f6282-76e1-47a0-960e-f62e529022b2","order_by":2,"name":"Yuheng Wu","email":"","orcid":"","institution":"Harvard University","correspondingAuthor":false,"prefix":"","firstName":"Yuheng","middleName":"","lastName":"Wu","suffix":""},{"id":352761261,"identity":"93180a91-542e-4d77-8b78-e3fdae10984f","order_by":3,"name":"Yuli Li","email":"","orcid":"","institution":"Harvard University","correspondingAuthor":false,"prefix":"","firstName":"Yuli","middleName":"","lastName":"Li","suffix":""},{"id":352761262,"identity":"82b966df-ac94-4444-9055-07d730ccb4d2","order_by":4,"name":"Richard Liu","email":"","orcid":"https://orcid.org/0000-0003-0951-6487","institution":"Harvard University","correspondingAuthor":false,"prefix":"","firstName":"Richard","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2024-08-27 21:35:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4986886/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4986886/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41557-025-01940-7","type":"published","date":"2025-09-22T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":64433101,"identity":"75070532-1a18-40a6-8a73-38f64dfad108","added_by":"auto","created_at":"2024-09-13 06:24:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":351247,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e production. \u003c/strong\u003eSchematics of \u003cstrong\u003ea,\u003c/strong\u003e Industrial H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production though t-AO process. \u003cstrong\u003eb,\u003c/strong\u003e Electrochemical H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production though the e-AO process.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4986886/v1/b2b297c06d0853a9691e1802.png"},{"id":64433103,"identity":"64ca3d41-3e37-4ae5-9d5d-08be8c3d65a9","added_by":"auto","created_at":"2024-09-13 06:24:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1771853,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eKinetics and thermodynamics of ANIHAT. \u003c/strong\u003eThe temporal variation of the mole fraction of H\u003csub\u003e2\u003c/sub\u003eDPPEAQ (red triangles) and DPPEAQ (blue triangles) using nonaqueous solvent compositions of \u003cstrong\u003ea,\u003c/strong\u003e 4Tol/1Dec,\u003cstrong\u003e b,\u003c/strong\u003e 3Tol/2Dec and\u003cstrong\u003e c,\u003c/strong\u003e 2Tol/3Dec. Results were fit by a second-order kinetics model (dashed line). Extracted constants of kinetics and thermodynamics are labeled respectively. \u003cstrong\u003ed,\u003c/strong\u003e SOC of H\u003csub\u003e2\u003c/sub\u003eDPPEAQ/DPPEAQ solution during ANIHAT under vigorous stirring using nonaqueous solvents with different polarity. \u003cstrong\u003ee,\u003c/strong\u003e The efficiency of ANIHAT using nonaqueous solvents with different polarity. \u003cstrong\u003ef,\u003c/strong\u003e The solubility of EtAQ in the nonaqueous phase and the reaction equilibrium constant (\u003cem\u003eK\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e) of ANIHAT using nonaqueous solvents with different polarity.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4986886/v1/bb83763af1d53b6123f0fc2b.png"},{"id":64433104,"identity":"46641b3a-5d32-4426-a0af-b5d8699ac572","added_by":"auto","created_at":"2024-09-13 06:24:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":429699,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePerformance of the e-AO process for H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e production. a,\u003c/strong\u003e Device for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production through the e-AO process. The three major parts are framed. Components and materials are labeled accordingly. Arrows indicate the flow direction during steady state production.\u003cstrong\u003e b,\u003c/strong\u003e The charge and discharge capacity and Coulombic efficiency of the EChem process. \u003cstrong\u003ec,\u003c/strong\u003e The charge and discharge capacity and Coulombic efficiency of EChem + ANIHAT process. Cycling of DPPEAQ is shaded in red. Cycling of DPPEAQ with EtAQ is shaded in yellow. Nonaqueous EtAQ solution was added as labeled. \u003cstrong\u003ed,\u003c/strong\u003e The FE of the e-AO process and corresponding H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration under varying water ratios to nonaqueous phase during the extraction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003cstrong\u003e e,\u003c/strong\u003e The temporal variation of FE and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration in the product during the continuous H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4986886/v1/d25ccdecb214a64a1a71abee.png"},{"id":64433105,"identity":"53bd8b64-9604-460b-8131-0e054f7d996f","added_by":"auto","created_at":"2024-09-13 06:24:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":839432,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGeneral e-AO method. a,\u003c/strong\u003e Schematics of e-AO method with flexible selection of counter electrode reaction, aqueous quinone and nonaqueous quinone. Circuit for electrochemical tests is drawn at the top. Cell structures, materials, molecules, reactions and charge carrier flows are labeled accordingly. \u003cstrong\u003eb,\u003c/strong\u003e Full cell polarization performance of DPPEAQ (20% SOC) and DHAQDS (20% SOC) against acidic HOR, acidic OER, and alkaline OER.\u003cstrong\u003e c, \u003c/strong\u003ePolarization (half-cell, converted to vs. SHE)and Coulombic efficiency of DPPEAQ (pH = 7). \u003cstrong\u003ed, \u003c/strong\u003ePolarization (half-cell, converted to vs. SHE) and Coulombic efficiency of DHAQDS (pH = 0). \u003cstrong\u003ee,\u003c/strong\u003e ANIHAT between aqueous AQs and EtAQ. Both aqueous and nonaqueous quinones were at 0.05 mol L\u003csup\u003e−1\u003c/sup\u003e.\u003cstrong\u003e f,\u003c/strong\u003e ANIHAT between aqueous AQs and NQ. Higher redox potential of NQ results in thermodynamically more favorable ANIHAT into nonaqueous phase. \u003cstrong\u003ef,\u003c/strong\u003e Comparison of different electrochemical indirect H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e synthesis methods\u003csup\u003e17-19\u003c/sup\u003e. Colors of the points indicate the accessible or demonstrated concentration of produced H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, which are reported in Supplementary Table S2. The colored shades represent the trend of the properties regarding different strategies.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4986886/v1/d1b22016df4de03a7bf410c6.png"},{"id":91955387,"identity":"5225db73-540b-4766-8a0a-c2c3a7f13ec4","added_by":"auto","created_at":"2025-09-23 07:09:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4645106,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4986886/v1/c66bf4f5-adae-4e8e-b578-5de4081e97bc.pdf"},{"id":64433102,"identity":"ad1c29dc-0fd7-43be-93ff-0cb0cd448c18","added_by":"auto","created_at":"2024-09-13 06:24:16","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":497900,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTOC:\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4986886/v1/495277b652c31ca6dce5cf9b.png"},{"id":64433106,"identity":"e9500d2a-733a-4ea9-9272-e7a93a832b3b","added_by":"auto","created_at":"2024-09-13 06:24:16","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":16773477,"visible":true,"origin":"","legend":"","description":"","filename":"ElectrifyingindustrialH2O2productionSI.docx","url":"https://assets-eu.researchsquare.com/files/rs-4986886/v1/f255b78c998038e3b4350371.docx"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nA patent related to the technique included in this manuscript has been submitted.","formattedTitle":"Electrifying Industrial Hydrogen Peroxide Production via Interfacial Molecular Mediation","fulltext":[{"header":"Highlights","content":"\u003col\u003e\n\u003cli\u003eUsing kinetically fast interfacial molecular mediation, we achieved a record high current density and efficiency of continuous electrochemical indirect H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e synthesis (Fig. 4g), overcoming drawbacks of using noble metal or amphiphilic molecules.\u003c/li\u003e\n\u003cli\u003eWe obtained ~100% selectivity of aqueous-nonaqueous interfacial hydrogen atom transfer, overcoming the selectivity issue in incumbent and reported Pd hydrogenation methods.\u003c/li\u003e\n\u003cli\u003eWe systematically studied the thermodynamics and kinetics of the heterogenous interfacial molecular catalytic hydrogen atom transfer, enabling the electrification of other selective nonaqueous chemical processes due to the fast kinetics of interfacial reactions.\u003c/li\u003e\n\u003cli\u003eThe e-AO method has the feasibility of tuning and pairing molecular mediators in both the aqueous and nonaqueous phase.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Main","content":"\u003cp\u003eHydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) is a strong, green oxidant with a wide variety of applications. At present, over 90% of industrial H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is manufactured through a thermocatalytic hydrogenation\u0026ndash;anthraquinone oxidation (abbreviated as t-AO) sequence\u003csup\u003e1\u003c/sup\u003e. This batchwise and indirect synthesis involves three key steps (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea): 1. hydrogenation of non-aqueous-soluble anthraquinones (AQs) by grey H\u003csub\u003e2\u003c/sub\u003e from steam methane reforming (Eq.\u0026nbsp;(\u003cspan refid=\"Equ9\" class=\"InternalRef\"\u003e1\u003c/span\u003e)); 2. oxidation of the resulting reduced AQs by air, producing H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)); 3. extraction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e by water. Because the nonaqueous solution and the AQs utilized are not soluble in water whereas H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e has a low solubility in nonaqueous solutions, t-AO is capable of producing high concentration, high purity H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e with high selectivity. The hydrogenation process to form the H\u003csub\u003e2\u003c/sub\u003eAQ, however, requires pressurized hydrogen input and palladium-based catalysts that can over-reduce AQs to unreactive compounds. Moreover, a considerable amount of energy and associated CO\u003csub\u003e2\u003c/sub\u003e emissions are associated with the production, distillation, and transport of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. Therefore, electrochemical methods for decentralized H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production are highly desired.\u003csup\u003e2\u003c/sup\u003e\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{H}_{2}\\left(methane-derived\\right)+AQ\\:\\left(nonaq\\right)\\underrightarrow{Pd}{H}_{2}AQ\\left(nonaq\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{O}_{2}\\left(air\\right)+{H}_{2}AQ\\left(nonaq\\right)\\to\\:AQ\\left(nonaq\\right)+{H}_{2}{O}_{2}(nonaq,\\:extracted\\:by\\:water)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eRecently, the on-site synthesis of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e has received significant attention\u003csup\u003e3, 4\u003c/sup\u003e, mostly focusing on development of catalysts\u003csup\u003e5\u0026ndash;7\u003c/sup\u003e. However, aqueous electrolysis systems require ions as the charge carrier. If the system is not designed properly, impurities such as ions and additives in the electrolytes end up in the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e product, necessitating additional costly purification.\u003csup\u003e8, 9\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eWith the goal of pure H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production, direct electrolysis methods utilizing gas diffusion electrode (GDE) engineering\u003csup\u003e10\u003c/sup\u003e, metal hydrides\u003csup\u003e11\u003c/sup\u003e, and the incorporation of solid electrolytes in multi-chamber cells\u003csup\u003e12, 13\u003c/sup\u003e have been reported. Although some studies have showcased impressively high current density and selectivity\u003csup\u003e14\u003c/sup\u003e, the direct electrolysis methods for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production still face the challenge of producing high H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations without experiencing severe declines in Faradaic efficiency. This occurs because increasing the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration shifts the equilibrium of the oxygen reduction reactions (ORRs), suppressing the 2e\u003csup\u003e\u0026ndash;\u003c/sup\u003e pathway to H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and promoting the competing 4e\u003csup\u003e\u0026ndash;\u003c/sup\u003e pathway toward H\u003csub\u003e2\u003c/sub\u003eO\u003csup\u003e12\u003c/sup\u003e. Additionally, the direct synthesis of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e through the 2e\u003csup\u003e\u0026minus;\u003c/sup\u003e ORR relies on GDEs to facilitate O\u003csub\u003e2\u003c/sub\u003e mass transport, whereas GDEs are highly susceptible to performance failures caused by flooding\u003csup\u003e15, 16\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn contrast, indirect production of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, which uses nonaqueous anthraquinone to mediate the 2e\u003csup\u003e\u0026ndash;\u003c/sup\u003e ORR, exhibits minimal impact of product concentration on Faradaic efficiency, if electrified. Moreover, the replacing of the cathodic ORR with the electroreduction of flowable molecules mediating 2e\u003csup\u003e\u0026minus;\u003c/sup\u003e ORR eliminates the need for GDEs, allowing utilization of more robust electrodes. For electrifying indirect H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e synthesis, researchers have examined phase transfer catalysis\u003csup\u003e17\u003c/sup\u003e, emulsions\u003csup\u003e18\u003c/sup\u003e and Pd membrane devices\u003csup\u003e19\u003c/sup\u003e to overcome the electrochemical limitations of nonaqueous solvents used for AO. Nevertheless, these reported H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e synthesis methods still fall short of simultaneously meeting all critical target criteria: high concentration, high purity, high current density, high efficiency, scalability, and low cost.\u003csup\u003e20\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eHerein, we report an electrochemical hydrogenation \u0026ndash; anthraquinone autoxidation (abbreviated as e-AO) with four separate steps (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb): 1. electrochemical hydrogenation; 2. aqueous-nonaqueous interfacial hydrogen atom transfer (ANIHAT); 3. anthraquinone oxidation (AO), producing H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e; and 4. H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e extraction. Different redox-active AQs were used as the hydrogen-atom carriers in each of the two immiscible phases. We utilized 2,6-bis(3-phosphonopropyl-1-oxy)anthraquinone (DPPEAQ, aqueous AQ)\u003csup\u003e21\u003c/sup\u003e in the neutral pH aqueous phase (aq), and 2-ethylanthraquinone (EtAQ, nonaqueous AQ) in the nonaqueous phase (nonaq). Each AQ displays high solubility in its corresponding phase and poor solubility in the other, ensuring exceedingly low AQ loss rate by crossover into the other phase. During the operation, DPPEAQ is first reduced in an aqueous electrochemical cell (Equations (\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e)). Then, H\u003csub\u003e2\u003c/sub\u003eDPPEAQ serves as a mediator, reducing EtAQ through ANIHAT (Eq.\u0026nbsp;(\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e5\u003c/span\u003e)), a heterogeneous molecular catalytic process.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:Anode:\\:\\:{H}_{2}O\\to\\:{0.5O}_{2}+2{H}^{+}+2{e}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:Cathode:\\:\\:DPPEAQ\\left(aq\\right)+2{e}^{-}{+2{H}^{+}\\to\\:H}_{2}DPPEAQ\\left(aq\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\:{H}_{2}DPPEAQ\\left(aq\\right)+EtAQ\\left(nonaq\\right)\\underleftrightarrow{interface}{DPPEAQ\\left(aq\\right)+H}_{2}EtAQ\\left(nonaq\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAfterward, the AO and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e extraction steps are carried out in the same manner as in t-AO processes. This method inherits the benefits from the t-AO process while avoiding its major drawbacks. The e-AO method decentralizes H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production powered by renewable electricity and circumvents the need for high pressure H\u003csub\u003e2\u003c/sub\u003e and the risk of AQ over-reduction. The ANIHAT process at the interface bridges the mass transport and thermodynamics of the aqueous and nonaqueous phase, transcending the challenges associated with electrochemical hydrogenation in the nonaqueous phase, even improving the selectivity of thermocatalytic hydrogenation during the t-AO. In addition, the facile reaction kinetics and high selectivity afforded by the ANIHAT process enable the e-AO method to stably produce H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e under steady-state conditions at a high current density and with high efficiency. The nonaqueous phase also prevents the contamination of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e by the solutes in the electrolytes, avoiding the need for costly downstream purification processes. This dual-phase system demonstrates wide tunability of aqueous and nonaqueous redox molecules and organic solvents, providing ample space for further optimization and adaptation to other synthetic applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eAqueous-nonaqueous interfacial hydrogen atom transfer (ANIHAT)\u003c/h3\u003e\n\u003cp\u003eAqueous-soluble AQs have been developed for aqueous redox flow batteries and exhibit reversible, high efficiency, high current density electrochemical properties\u003csup\u003e22\u003c/sup\u003e. Yet solely using aqueous-soluble AQs for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrolysis is not sensible due to the coexistence of aqueous solutes in the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e product. In the e-AO process, the aqueous and nonaqueous AQs must remain exclusive within their respective phases to yield a pure aqueous solution of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. Instead of using a typical non-aqueous solvent (a blend of heavy aromatic compounds and polar solvents)\u003csup\u003e23\u003c/sup\u003e in the t-AO process, we used a mixture of toluene and 1-decanol (Tol/Dec). This choice of solvent system facilitates characterization and allows for fine-tuning of polarity while maintaining excellent phase separation from water. Utilizing ultraviolet-visible spectrophotometry (UV-Vis), we ascertained that DPPEAQ is virtually insoluble in the nonaqueous phase and that EtAQ does not dissolve in water (\u003cb\u003eSupplementary Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e \u0026ndash; S3, Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), prohibiting phase crossover of AQs. Consequently, redox processes between DPPEAQ and EtAQ are confined to the interface between the water and Tol/Dec. Using this system, we examined the kinetics and thermodynamics of the ANIHAT process \u0026ndash; a spontaneous, non-Faradaic proton-coupled electron transfer process occurring at the aqueous-nonaqueous phase boundary.\u003c/p\u003e \u003cp\u003eGiven that the ANIHAT is a heterogeneous molecular catalytic process happening at the interface, free energies of the reaction products and intermediates can be influenced by the polarity of the nonaqueous solvents. The kinetics and thermodynamics of the ANIHAT process should be tunable \u003cem\u003evia\u003c/em\u003e the solvent composition. To investigate the impact of nonaqueous solvent polarity on ANIHAT, kinetic experiments were conducted using the Tol/Dec solvent system with different volumetric ratios, using the abbreviated label \u003cem\u003en\u003c/em\u003eTol/\u003cem\u003em\u003c/em\u003eDec to denote \u003cem\u003en\u003c/em\u003e mL toluene mixed with \u003cem\u003em\u003c/em\u003e mL 1-decanol. In each kinetic test, 10 mL 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e H\u003csub\u003e2\u003c/sub\u003eDPPEAQ and 10 mL 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EtAQ were sequentially added into a 50 mL centrifuge tube inside a nitrogen-filled glovebox. Pumps were used to facilitate rapid mass transport in each phase, while maintaining a clear and stable aqueous-nonaqueous interface with an area of 6.2 cm\u003csup\u003e2\u003c/sup\u003e (\u003cb\u003eSupplementary Fig. S4\u003c/b\u003e). Intermittently, aliquots of the aqueous phase were collected for UV-Vis analysis. The temporal variations of the UV-Vis spectra of DPPEAQ/H\u003csub\u003e2\u003c/sub\u003eDPPEAQ in nonaqueous phases of different polarities are shown in \u003cb\u003eSupplementary Fig. S5a \u0026ndash; c\u003c/b\u003e. The absorbance at 355 nm were used to calculate the mole fractions of DPPEAQ and H\u003csub\u003e2\u003c/sub\u003eDPPEAQ (\u003cb\u003eSupplementary Fig. S6\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eRegressions of observed mole fractions as functions of time were conducted assuming ANIHAT as a reversible, second-order reaction (Equations \u003cspan refid=\"Equ6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Equ8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, \u003cb\u003eSupplementary Fig. S7\u003c/b\u003e). The apparent rate constants for the forward reaction (\u003cem\u003ek\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e) and for the reverse reaction (\u003cem\u003ek\u003c/em\u003e\u003csub\u003e\u0026minus;\u0026thinsp;1\u003c/sub\u003e) are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea \u003cb\u003e\u0026ndash; c\u003c/b\u003e. Here \u003cem\u003er\u003c/em\u003e represents the rate of the forward or backward reaction and A is the area of the aqueous-nonaqueous interface.\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$\\:{r}_{forward}=A{k}_{1}{[H}_{2}DPPEAQ\\left]\\right[EtAQ]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$\\:{r}_{backward}=A{k}_{-1}\\left[DPPEAQ\\right]{[H}_{2}EtAQ]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e\n$$\\:{K}_{eq}=\\frac{{k}_{1}}{{k}_{-1}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAs the volume fraction of 1-decanol, the more polar solvent, increased from 0.2 to 0.6, the equilibrium constant (\u003cem\u003eK\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e) increased from 0.03 to 0.29. Besides, \u003cem\u003ek\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e increased as the volume fraction of 1-decanol rises, whereas \u003cem\u003ek\u003c/em\u003e\u003csub\u003e\u0026minus;\u0026thinsp;1\u003c/sub\u003e first declines and then remains steady. DFT calculations supported the hypothesized mechanism of ANIHAT. In the model, hydrogen atom transfer occurs through a quinhydrone-like intermediate formed on the aqueous-nonaqueous interface\u003csup\u003e24\u003c/sup\u003e. According to the computations, concerted proton-coupled electron transfer (PCET) is associated with a lower-energy transition state than is separated, sequential electron, proton transfer (\u003cb\u003eSupplementary Fig. S8 \u0026ndash; S11\u003c/b\u003e) \u003csup\u003e25\u003c/sup\u003e. The quinhydrone intermediate allows fast PCET through the aqueous-nonaqueous interface\u003csup\u003e26\u003c/sup\u003e. For practical applications, vigorous agitation can substantially increase the interfacial area between the aqueous and nonaqueous phases, resulting in the attainment of charge equilibrium within only 3 s (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, \u003cb\u003eSupplementary Fig. S12\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eAfter sufficient agitation, we measured the charge capacity (in terms of electrons) leaving the aqueous phase (DPPEAQ donation) and the corresponding amount of capacity entering the nonaqueous phase (EtAQ reception). The efficiency of ANIHAT, defined as their ratio, was determined to be approximately 100% (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). A trade-off exists with respect to the solvent polarity: a higher 1-decanol fraction would increase the kinetics of the forward reaction and thermodynamic driving force of ANIHAT but, by decreasing the solubility of EtAQ, it is detrimental to mass transport and concentration of the final H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e product (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). To balance these factors, we chose a 3Tol/2Dec as the nonaqueous solvent for further evaluation of the e-AO method in full system tests.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eHO production using the e-AO process\u003c/h3\u003e\n\u003cp\u003eContinuous H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production through the e-AO process was conducted in a tandem reactor, with three major components: aqueous electrochemistry (labeled as EChem) for aqueous AQ hydrogenation, ANIHAT for hydrogenation of the nonaqueous AQ, AO for highly selective 2 e oxygen reduction reaction and product extraction. In total, two aqueous phases (a solution of DPPEAQ and one containing the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e product) and one nonaqueous phase (EtAQ solution) were used and cycled individually. During ANIHAT and AO, which require interfacial reaction/extraction between the aqueous and nonaqueous phase, mixers and separators were used to facilitate the phase mixing and separation, as labeled in (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cb\u003eSupplementary Fig. S13\u003c/b\u003e).\u003csup\u003e17\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eTo quantify the efficiency loss in each part, we first conducted a long-term cell cycling test of 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e DPPEAQ in 0.33 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e phosphate buffer (pH\u0026thinsp;=\u0026thinsp;7) in order to maintain the pH of the electrolyte near neutral during operation. The cell was cycled against ferro/ferricyanide in a nitrogen-filled glovebox, to evaluate the efficiency of the EChem step. We used a standard constant-current followed by constant-voltage (CCCV) protocol accessing more than 95% of theoretical capacity of the DPPEAQ side. The cell was cycled for 6 days and demonstrated a Coulombic efficiency of approximately 99%, with a fade rate of approximately 0.2% day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The fading was due to anthrone and dimer formation of DPPEAQ under near neutral conditions,\u003csup\u003e27\u003c/sup\u003e as we determined by liquid chromatography\u0026ndash;mass spectrometry (LC-MS) analysis (\u003cb\u003eSupplementary Fig. S14\u003c/b\u003e). These side-products could be recovered through electro-oxidation\u003csup\u003e28\u003c/sup\u003e or chemical treatments\u003csup\u003e29\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTo evaluate the compatibility of ANIHAT with EChem, after a few days cycling of only DPPEAQ in aqueous buffer, we added 3 mL of 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EtAQ in 3Tol/2Dec (theoretical capacity: 57.9 C) on top of the aqueous negolyte during cell cycling. The cell cycling capacity was found to increase from approximately 125 C to 180 C (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), indicating that the nonaqueous EtAQ could be cycled along with the aqueous phase, presumably due to fast reversible ANIHAT and the similarity of redox potentials between the EtAQ and DPPEAQ. The initial drop of Coulombic efficiency in the first cycle was due to the presence of residual oxygen dissolved in the nonaqueous phase. A roughly constant Coulombic efficiency attained afterward indicates that ANIHAT was successfully incorporated into the EChem process (charging and discharging) with a high efficiency. Post-cycling LC-MS analysis provided evidence of the high selectivity of ANIHAT, showing only trace amounts of anthrone/dimer formation from EtAQ (\u003cb\u003eSupplementary Fig. S15\u003c/b\u003e). The pH of the DPPEAQ solution is crucial because a pH lower than 7 leads to DPPEAQ precipitation, whereas a pH higher than 12 causes deprotonation of H\u003csub\u003e2\u003c/sub\u003eEtAQ, forming a water-soluble anion, EtAQ\u003csup\u003e2\u0026minus;\u003c/sup\u003e (\u003cb\u003eSupplementary Fig. S16\u003c/b\u003e)\u003csup\u003e30\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHaving confirmed high efficiency of EChem and ANIHAT working in tandem, we next sought to include AO in a complete process for hydrogen peroxide synthesis. First, we used DPPEAQ to mediate the reduction of 50 mL of 0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EtAQ in 3Tol/2Dec, which was added to the initially fully charged nonaqueous phase, and continued to charge the system until approximately 20% of EtAQ was reduced as H\u003csub\u003e2\u003c/sub\u003eAQ. At this point, the nonaqueous phase was agitated with air to completely oxidize H\u003csub\u003e2\u003c/sub\u003eEtAQ. Deionized water (DI water) in varying proportions to the nonaqueous phase was then used to extract the produced H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. The extraction was conducted twice. The concentration of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e products was determined by titration with KMnO\u003csub\u003e4\u003c/sub\u003e, from which the Faradaic efficiency (FE) was calculated based on the moles of obtained H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and the total moles of electrons injected into nonaqueous phase. The highest concentration of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e achieved in a single extraction trial was 3.2 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u0026gt;\u0026thinsp;10% wt.) at a water volumetric ratio of 0.015 to nonaqueous solvent (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The corresponding cumulative FE for two consecutive extractions was 75.7%, limited by the partition coefficient of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e between water and the nonaqueous solvent.\u003csup\u003e31\u003c/sup\u003e The FE of the whole process is about 85% when extraction efficiency is not limited, as verified by additional extraction.\u003c/p\u003e \u003cp\u003eFinally, we performed continuous H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production in the tandem reactor. During the electrolysis at 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in a 5 cm\u003csup\u003e2\u003c/sup\u003e flow cell, the cathode voltage remained stable (\u003cb\u003eSupplementary Fig. S17 \u0026ndash; S18\u003c/b\u003e). The H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solution in the product tank was sampled intermittently and titrated by KMnO\u003csub\u003e4\u003c/sub\u003e to determine the concentration of product and FE. As expected, low FE was observed at the beginning due to capacity being injected into aqueous and nonaqueous AQs in order to build up the state of charge before reaching steady state. Subsequently, the steady-state FE of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production was about 80%. The presence of residual oxygen in the nonaqueous phase after Separator 2 leading into Mixer 1 negatively influenced the FE (\u003cb\u003eSupplementary Fig. S19 \u0026ndash; S20\u003c/b\u003e). During continuous production, the concentration of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e increased almost linearly with time, reaching 0.055 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (1.9% wt.) after 1000 s (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eGeneralization of the e-AO process\u003c/h3\u003e\n\u003cp\u003eThe e-AO concept allows for flexible selection of anode reactions, as well as choice of aqueous AQs and nonaqueous quinones, providing space for further optimization and other applications. In principle, the anodic reaction of e-AO could be any oxidation reaction, provided the ion charge carriers into the cathode are protons. For example, we show that the hydrogen oxidation reaction (HOR) against a cation exchange membrane (CEM),\u003csup\u003e9\u003c/sup\u003e acidic oxygen evolution reaction (OER) against a CEM,\u003csup\u003e19\u003c/sup\u003e or alkaline OER against a bipolar membrane (BPM) can be used on the anode side\u003csup\u003e32\u003c/sup\u003e. These reactions, molecular candidates, and charge carriers are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. During our tests, the cell was monitored with two voltmeters, one recording the full cell voltage (full cell voltage V\u003csub\u003e1\u003c/sub\u003e, positive), another connecting the working electrode and a reference electrode inserted in aqueous AQ catholyte (referenced V\u003csub\u003e2\u003c/sub\u003e). V\u003csub\u003e2\u003c/sub\u003e was converted to cathode voltage vs. standard hydrogen electrode (SHE).\u003c/p\u003e \u003cp\u003eThe full cell polarization test was conducted using the negolytes of 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e buffered DPPEAQ (pH\u0026thinsp;=\u0026thinsp;7, 20% SOC) or 0.25 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e 1,8-dihydroxy-9,10-anthraquinone-2,7-disulphonic acid (DHAQDS, pH\u0026thinsp;=\u0026thinsp;0, 20% SOC) against acidic HOR, acidic OER and alkaline OER \u003csup\u003e22\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). The cathode voltage was subtracted from the full cell voltage V\u003csub\u003e1\u003c/sub\u003e to gain insight into the properties of the counter reactions and cross-membrane resistance (\u003cb\u003eSupplementary Fig. S21\u003c/b\u003e). Notably, the cells working with an acidic catholyte delivered better polarization performance than those working with a pH-neutral catholyte, due to the elimination of the pH gradient and the reduction of ion polarization resistance across the membrane. For each kind of counter reaction, the HOR has the lowest energy cost but consumes hydrogen gas and, in our setup, utilizes a Pt/C gas diffusion electrode (GDE). The acidic OER with a CEM does not use hydrogen or a GDE, yet commonly requires noble-metal catalysts.\u003csup\u003e33\u003c/sup\u003e The alkaline OER with a BPM is a noble-metal-free alternative. The greater polarization resistance compared to acidic OER is attributable to the higher resistance of the BPM, indicating a need for further development of more effective BPMs.\u003csup\u003e34\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe selection of aqueous AQs offered an opportunity for tuning the kinetics and thermodynamics during electrochemical hydrogenation and thus affecting the accessible current density and efficiency. We conducted measurements of the polarization performance of DPPEAQ and DHAQDS under different SOC and the corresponding Coulombic efficiency at low SOC (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). The Coulombic efficiency drop for DPPEAQ when the current density is greater in magnitude than 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e is caused by the pH gradient generated in the cell. Locally low pH on the near membrane side of the cathode under high current density boosts hydrogen evolution (HER) (\u003cb\u003eSupplementary Fig. S22\u003c/b\u003e). DHAQDS showed lower overpotential than DPPEAQ, delivering 400 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at \u0026minus;\u0026thinsp;0.3 V vs SHE with 98.8% Coulombic efficiency. This is due to the uniform pH distribution in the acidic solution when using protons as charge carriers across the membrane. To show the practical feasibility of our method, we further tested the polarization of 2,2\u0026rsquo;-((9,10-dioxo-9,10-dihydroanthracene-2,6-diyl)bis(oxy))dipropionic acid (D2PEAQ) (\u003cb\u003eSupplementary Fig. S23\u003c/b\u003e), which is a considerably cheaper and synthetically accessible molecule, demonstrating higher solubility (0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) near neutral pH.\u003csup\u003e35\u003c/sup\u003e D2PEAQ also has a slightly more negative redox potential than DPPEAQ, which should facilitate the ANIHAT process, but at the expense of higher energy cost (\u003cb\u003eSupplementary Fig. S24\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eTo examine the variation in spontaneity of ANIHAT among different aqueous and nonaqueous quinone pairs, the extent of reaction between three aqueous H\u003csub\u003e2\u003c/sub\u003eAQ and two nonaqueous quinones (EtAQ and naphthoquinone (NQ)) was measured (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee \u003cb\u003e\u0026ndash; f\u003c/b\u003e). NQs are also commonly used in t-AO H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e synthesis, but have a higher redox potential and a slower AO kinetics than AQs.\u003csup\u003e23, 36\u003c/sup\u003e The ANIHAT between H\u003csub\u003e2\u003c/sub\u003eD2PEAQ and NQ exhibited the highest thermodynamic spontaneity, even demonstrating promise for the utilization of low polarity organic solvents (toluene only). This suggests the potential to reduce organic solvent waste in the AO process, because higher polarity organic solvents can dissolve slightly in the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e product, and removal of that contamination requires a large amount of heavy aromatic solvent as extracting agent.\u003csup\u003e2\u003c/sup\u003e It is also worth noticing that the ANIHAT process occurs exclusively when there is compatibility between the hydrogen atom donor and acceptor.\u003csup\u003e37\u003c/sup\u003e When the aqueous AQ is instead replaced with a phenazine (2,2\u0026prime;-(phenazine-1,8-diyl)bis(ethane-1-sulfonate)), a viologen (methyl viologen), or vanadium (V\u003csup\u003e2+\u003c/sup\u003e), in all cases paired with nonaqueous EtAQ, there was no significant charge transfer detected within a brief period although, according to the relevant redox potentials, the reaction is thermodynamically favored in all cases. Without formation of a suitable ANIHAT complex at the interface, such as a quinhydrone in the case of anthraquinone couples,\u003csup\u003e24\u003c/sup\u003e interfacial charge and proton transfers have a high energy barrier and slow kinetics.\u003csup\u003e38\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eOwing to the kinetics and selectivity of electrochemistry of aqueous AQs and ANIHAT, the e-AO method stands out due to its capability of producing H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e with high concentration, high FE, and a high H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e yield rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg).\u003csup\u003e10, 17, 19\u003c/sup\u003e Techno-economic analysis shows the potential of commercializing e-AO using green electricity, leading to an intriguing levelized cost of produced H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (\u003cb\u003eSupplementary Fig. S25\u003c/b\u003e). Flexibility of molecules and operating conditions are expected to lead to other applications and further optimization in the future.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eOutlook\u003c/h3\u003e\n\u003cp\u003eAchieving highly selective and efficient electrochemical reactions in nonaqueous phases remains a significant challenge. However, nonaqueous phases are often essential for specific reactions, offering advantages such as optimal solvent polarity or automatic phase separation from aqueous systems. In contrast, aqueous-phase electrochemistry is typically more cost-effective and efficient due to lower ionic resistance but often struggles with separating products from the aqueous electrolyte\u003csup\u003e39, 40\u003c/sup\u003e. We demonstrated a solution for this paradox by developing an electrified hydrogen peroxide production system.\u003c/p\u003e \u003cp\u003eThrough a comprehensive investigation of the mechanism and kinetic behavior of ANIHAT, we electrified the conventional t-AO process using aqueous electrochemistry. The e-AO process, with its flexibility in molecule, solvent, and anode choices, operates at high current densities with excellent Faradaic efficiency, yielding high-concentration, pure H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e product. The process overcomes the selectivity and stability challenges of the incumbent t-AO process and enables the decentralized H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production. With future chemical and molecular engineering regarding nonaqueous solvents and ANIHAT redox pairs, the e-AO process has the potential to be scaled up, significantly diminishing organic waste and leading to better performance. The e-AO process can also facilitate the electrification of other applications that require peroxides, like the synthesis of alkyl oxides, selective oxidation of chemicals and water treatment. Furthermore, it has the potential to substitute H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e for emissions-intensive feedstocks in the creation of new routes for process intensification of high-value chemicals\u003csup\u003e41\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eMore broadly, this work highlights the potential of integrating nonaqueous chemistry in organic phases with aqueous electrochemistry through interfacial chemical reactions. Unlike traditional phase-transfer catalysis, ANIHAT selectively transports only hydrogen atoms, rather than amphiphilic molecules, between phases. The formation of interfaces across which highly selective facile mass and energy transport occur should significantly benefit chemical synthesis processes by eliminating the requirement for further purification or separation\u003csup\u003e42\u0026ndash;44\u003c/sup\u003e. With judicious selection of the chemical intermediates, the kinetics of the interfacial reaction can be sufficiently rapid\u003csup\u003e38, 45\u003c/sup\u003e for scalable applications using phases that are selective to the mass transport of certain species and feature automatic phase separation\u003csup\u003e40, 46\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e \u003cb\u003eMaterials and synthesis.\u003c/b\u003e 2,6-Bis(3-phosphonopropyl-1-oxy)anthraquinone (DPPEAQ) was purchased from TCI Chemicals\u003csup\u003e21\u003c/sup\u003e. Nafion\u0026reg; 212 as cation exchange membrane and Fumasep\u0026reg; FBM as bipolar membrane were purchased and only soaked in DI water before usage. Ir/C, Ni foam, hydrophobic carbon paper, 5 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e Pt gas diffusion electrode (GDE) were purchased from fuel cell store. Potassium permanganate (KMnO\u003csub\u003e4\u003c/sub\u003e), sodium oxalate (Na\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e), dipotassium phosphate (K\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e), monopotassium phosphate (KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e), sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e), potassium hydroxide (KOH), potassium ferricyanide (K\u003csub\u003e3\u003c/sub\u003eFe(CN)\u003csub\u003e6\u003c/sub\u003e), potassium ferrocyanide (K\u003csub\u003e4\u003c/sub\u003eFe(CN)\u003csub\u003e6\u003c/sub\u003e). 2-ethylanthraquinone (EtAQ), naphthoquinone (NQ), 2,6-dihydroxyl-9,10-anthraquinone (DHAQ) and 1,8-dihydroxy-9,10-anthraquinone-2,7-disulphonic acid, sodium salt were purchased from Sigma-Aldrich. 1,8-dihydroxy-9,10-anthraquinone-2,7-disulphonic acid (DHAQDS) was prepared using a cation exchange resin column filled with Amberlyst\u0026reg; 15(H) to exchange sodium ions into protons\u003csup\u003e22\u003c/sup\u003e. 2,2\u0026rsquo;-((9,10-dioxo-9,10-dihydroanthracene-2,6-diyl)bis(oxy))dipropionic acid (D\u003csub\u003e2\u003c/sub\u003ePEAQ) was synthesized according to our previous report.\u003csup\u003e35\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrode preparation.\u003c/b\u003e Electrodes for aqueous electrolyte tests are carbon papers (SGL 39AA) baked at 400\u0026deg;C overnight. Carbon paper loaded with about 1 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e Ir/C was served for acidic OER. Typically, 10 mg of Ir/C catalysts, 0.97 mL of 2-propanol and 30 \u0026micro;L of Nafion binder solution were mixed to form a catalyst ink. The ink was sonicated for about 30 min and then spray coated on carbon paper. Ni foam loaded with NiFe hydroxides was served for alkaline OER. The electrode was prepared by electrodeposition washed\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO (0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and FeSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;7H\u003csub\u003e2\u003c/sub\u003eO (0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) under \u0026minus;\u0026thinsp;10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for 1 min, and was washed with DI water.\u003c/p\u003e \u003cp\u003e \u003cb\u003eH\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eO\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003edetection.\u003c/b\u003e The concentration of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was detected by a standard KMnO\u003csub\u003e4\u003c/sub\u003e titration process. KMnO\u003csub\u003e4\u003c/sub\u003e solution was prepared by dissolving 7.9 g KMnO\u003csub\u003e4\u003c/sub\u003e in 1 L of 1 N H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (about 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e KMnO\u003csub\u003e4\u003c/sub\u003e, 0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e), then was boiled and stored in brown reagent bottles in the dark. The exact concentration of KMnO\u003csub\u003e4\u003c/sub\u003e was calibrated by titrating with a standard Na\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e solution at about 70\u0026deg;C.\u003c/p\u003e \u003cp\u003e \u003cb\u003eAnalytical concentration and SOC detection.\u003c/b\u003e The analytical concentration and state of charge (SOC) of DPPEAQ were measured by UV-Vis spectrophotometry. We defined the analytical concentration (c\u003csub\u003eA\u003c/sub\u003e) as the total concentration of DPPEAQ and H\u003csub\u003e2\u003c/sub\u003eDPPEAQ, and the SOC as the concentration of H\u003csub\u003e2\u003c/sub\u003eDPPEAQ divided by c\u003csub\u003eA\u003c/sub\u003e. In each test, the electrolyte sample was collected and diluted to the detection range with 1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e KOH in a nitrogen filled glove box. The KOH was purged with N\u003csub\u003e2\u003c/sub\u003e for 15 min to get rid of the residual O\u003csub\u003e2\u003c/sub\u003e in advance. The absorbance within the wavelength range of 200 nm to 800 nm were then recorded by UV-Vis spectrophotometry (Agilent Cary 60 spectrometer). The absorbance at the wavelengths of 355 nm and 408 nm were ascribed to DPPEAQ (SOC\u0026thinsp;=\u0026thinsp;0%) and H\u003csub\u003e2\u003c/sub\u003eDPPEAQ (SOC\u0026thinsp;=\u0026thinsp;100%), respectively. By varying c\u003csub\u003eA\u003c/sub\u003e, we calibrated the concentration-absorbance curves. The concentration-absorbance curves of EtAQ was calibrated following the same procedures.\u003c/p\u003e \u003cp\u003eWe obtained DPPEAQ solutions with a series of SOCs by mixing 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e DPPEAQ and 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e H\u003csub\u003e2\u003c/sub\u003eDPPEAQ in varying proportions. The absorbance at the wavelength of 355 nm (A\u003csub\u003e355\u003c/sub\u003e) exbibits a strong linear relationship with SOC. Therefore, at a specific c\u003csub\u003eA\u003c/sub\u003e, the SOC could be calculated as Equation S1:\u003cdiv id=\"Equ9\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ9\" name=\"EquationSource\"\u003e\n$$\\:x=\\frac{{A}_{355,SOC=0}-{A}_{355,SOC=x}}{{A}_{355,SOC=0}-{A}_{355,SOC=1}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003eS1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cem\u003ex\u003c/em\u003e is the SOC to be determined.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSolubility test.\u003c/b\u003e The solubility of DPPEAQ, D\u003csub\u003e2\u003c/sub\u003ePEAQ, and EtAQ was measured by adding each compound into the corresponding solutions under sonication until no further solids could be dissolved. The saturated solution was then diluted, and its concentration was determined by UV-Vis spectrophotometry. The concentration was calculated according to a pre-calibrated absorbance-concentration curve. In addition, the solubility of DPPEAQ in the nonaqueous phase and that of EtAQ in the aqueous phase were measured following the same procedure without the dilution step.\u003c/p\u003e \u003cp\u003e \u003cb\u003eANIHAT kinetics measurement.\u003c/b\u003e The kinetic rate constants involved in ANIHAT were measured using several nonaqueous phase polarities in a nitrogen glovebox. The aqueous phase consisted of a solution containing 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of DPPEAQ dissolved in 0.33 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e phosphate buffer with a pH of 7, which we call buffered DPPEAQ. The nonaqueous phase was 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EtAQ dissolved in nTol/mDec. Both the aqueous and nonaqueous phases were purged of dissolved O\u003csub\u003e2\u003c/sub\u003e with nitrogen prior to being transferred into the glovebox. DPPEAQ was first charged to a SOC of 100% under a CCCV protocol against buffered ferro/ferricyanide. The cutoff voltage for 20 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e constant current was set as 1.2 V, and the voltage was held until the current density dropped in magnitude to below 0.2 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Then, 20 mL of DPPEAQ were transferred to a 50 mL centrifuge tube and 20 mL of EtAQ was added onto the top of H\u003csub\u003e2\u003c/sub\u003eDPPEAQ carefully without mixing or splashing. The aqueous-nonaqueous interfacial area was 6.2 cm\u003csup\u003e2\u003c/sup\u003e. The meantime, two KNF pumps consistently circulated the aqueous and nonaqueous phase respectively at 20 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e while not disrupting the interface between them. A timer was started when nonaqueous solution was added. At regular intervals, 0.5 mL of aqueous and nonaqueous samples were taken out from each phase and diluted using 1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e KOH by a factor of 500 for UV-Vis analysis, until the SOC of DPPEAQ reached equilibrium. Based on a reversible second-order kinetic model, the apparent kinetic constants were derived.\u003c/p\u003e \u003cp\u003eThe kinetics test of ANIHAT under vigorous stirring was performed in the N\u003csub\u003e2\u003c/sub\u003e glovebox. In a mixer, after 3 seconds of vigorous stirring and standing still until clear phase separation, 0.5 mL aqueous phase were taken out and diluted for UV-Vis.\u003c/p\u003e \u003cp\u003e \u003cb\u003eANIHAT test for various redox couples\u003c/b\u003e. The efficiency of ANIHAT and the spontaneity of ANIHAT with different combinations of aqueous anthraquinones (DPPEAQ, D2PEAQ, DHAQDS) and nonaqueous quinones (EtAQ, naphthoquinone) in toluene or 3Tol/2Dec were conducted by measuring the extent of reaction between 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e aqueous H\u003csub\u003e2\u003c/sub\u003eAQ and 0.05 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e nonaqueous quinones in the N\u003csub\u003e2\u003c/sub\u003e glovebox. First, 5 mL aqueous AQ solutions were charged to 100% SOC with CCCV protocol. The recorded capacity was regarded as the overall capacity. Next, 5 mL nonaqueous quinone solution was added to the aqueous phase. After a sufficient amount of stirring, the emulsion was allowed to settle until it separated into two distinct phases. Recharging the separated aqueous solution using the same CCCV protocol allowed for the determination of the charge transferred throughout the ANIHAT procedure. The extent of reaction was determined by dividing the transferred charge by the total charge. UV-Vis spectrophotometry was used to cross confirm the state of charge of aqueous AQs before and after ANIHAT.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCycling of DPPEAQ.\u003c/b\u003e The cycling test of DPPEAQ was conducted by employing the constant current followed by constant voltage (CCCV) protocol. A cell composed of 10 mL 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e buffered DPPEAQ paired with 100 mL of 0.08 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e ferrocyanide\u0026thinsp;+\u0026thinsp;0.02 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e ferricyanide. Excess capacity in the posolyte ensured that DPPEAQ was the capacity limiting side of the cell. The two half-cells were separated by a Nafion 212 membrane. Two layers of carbon paper were used in each half-cell. The flow rate of electrolytes was set to be 60 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The cell was cycled at a constant current of 20 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, followed by a constant charging voltage of 1.2 V and discharging voltage of 0.3 V until the current drops to 0.2 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe cycling test of DPPEAQ\u0026thinsp;+\u0026thinsp;EtAQ was conducted using the same protocol. DPPEAQ initially underwent 32 consecutive cycles, followed by the addition of 3 mL of 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EtAQ in 3Tol/2Dec on top of it. Subsequently, an additional 5 cycles were conducted.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePerformance test of H\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eO\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eproduction.\u003c/b\u003e The production of high concentration H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was conducted batchwise. 10 mL 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e buffered DPPEAQ and 50 mL 0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EtAQ in 3Tol/2Dec was charged against acidic OER. While charging, N\u003csub\u003e2\u003c/sub\u003e gas was continuously purged above the solution to prevent the oxidation of H\u003csub\u003e2\u003c/sub\u003eEtAQ by O\u003csub\u003e2\u003c/sub\u003e. As the SOC of EtAQ went higher, the color of nonaqueous phase turned dark green. After the SOC of EtAQ reached approximately 20%, the charging was stopped and the DPPEAQ solution was removed from the nonaqueous phase. Next, the nonaqueous phase was exposed to air for oxidation. DI water in varying proportion to the nonaqueous phase was then added to extract the produced H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. The extraction was conducted twice. The concentration of generated H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was titrated by KMnO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThe continuous H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production was conducted in the tandem reactor\u003csup\u003e17\u003c/sup\u003e. Specifically, 18 mL DPPEAQ (0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e DPPEAQ in 0.33 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e phosphate pH 7 buffer) and 18 mL pure water were stored in the catholyte tank and the product tank, respectively, and continuously pumped through the corresponding mixers and separators. 30 mL 0.25 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EtAQ phase was then added and circulated on the top of them. The flow rate was about 20 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. When a negative potential was applied to the cathode, DPPEAQ was hydrogenated and transported to Mixer 1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). In Mixer 1, the DPPEAQ phase mixed with the EtAQ phase under vigorous stirring, ensuring the ANIHAT was conducted thoroughly. Subsequently, the EtAQ phase carrying H\u003csub\u003e2\u003c/sub\u003eEtAQ was transported to Mixer 2, mixing with air and the H\u003csub\u003e2\u003c/sub\u003eO phase. The generated H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e accumulated in the product tank, and the oxidized EtAQ was circulated back to Mixer 1, moving on to the next reaction round. The mass flow of air was controlled to minimize oxygen residue in the non-aqueous phase to avoid the unwanted oxidation of the reduced DPPEAQ. Within the continuous production of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, a current of 250 mA was employed, with a corresponding area of 5 cm\u003csup\u003e2\u003c/sup\u003e. During the electrolysis, the cathode potential was recorded using a voltmeter connected to the cathode and a reference electrode inserted in the catholyte. Every 200 s, 0.5 mL of the aqueous phase was taken out from the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e collection tank for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e detection. Before and after the electrolysis, electrochemical impedance spectroscopy (EIS) measurements were conducted with 10 mV perturbation and with frequency ranging from 1 to 100000 Hz to determine the high-frequency area-specific resistance (ASR).\u003c/p\u003e \u003cp\u003e \u003cb\u003ePolarization test\u003c/b\u003e. The full cell polarization test was conducted with different combinations of anode reactions, membranes, and cathode pH. The potential was swept from open circuit voltage at a scan rate of 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using linear sweep voltammetry (LSV) controlled through the full cell voltage V\u003csub\u003e1\u003c/sub\u003e, and the resulting current response was measured. During tests, the cell was monitored with two voltmeters, one recording the full cell voltage (V\u003csub\u003e1\u003c/sub\u003e) and another recording the cathode potential (V\u003csub\u003e2\u003c/sub\u003e). The corresponding current was recorded.\u003c/p\u003e \u003cp\u003eThe polarization performance of the cathode was evaluated using 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e buffered DPPEAQ, 0.25 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e buffered D2PEAQ and 0.25 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e DHAQDS in 0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. The cell was first charged to certain SOCs with respect to theoretical capacity. Then, LSV was conducted through sweeping the full cell voltage V\u003csub\u003e1\u003c/sub\u003e at a scan rate of 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with half-cell voltage V\u003csub\u003e2\u003c/sub\u003e measured using a reference electrode inserted in the catholyte. The half-cell LSV and OCV results (converted to vs. SHE) were determined based on V\u003csub\u003e2\u003c/sub\u003e and the corresponding current density.\u003c/p\u003e \u003cp\u003e \u003cb\u003eQuantum Chemistry computations.\u003c/b\u003e Detailed computational methods, which include all meta data and formula development, are described in the Supplementary Information. Generally, the geometry optimization of the quinhydrone analog intermediate was conducted based on density functional theory calculations (DFT), as performed using the Vienna \u003cem\u003eab initio\u003c/em\u003e simulation package (VASP). The calculation of the potential energy surface of ANIHAT was accomplished using Gaussian 16 package.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e: All data are available in the manuscript or the supplementary materials.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e This research was supported by Harvard Climate Change Solutions Fund, Harvard Dean\u0026apos;s Competitive Fund and by the Harvard School of Engineering and Applied Sciences.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors Contributions Statement\u003c/strong\u003e: D.X. conceived the idea. D.X. and Y.W. designed and conducted hardware design, tests and electrochemical experiments. Y.L. did the DFT calculation. R.Y.L. supervised the reaction mechanism study. M.J.A. supervised the project. D.X., Y.W. and M.J.A. drafted the manuscript. All authors edited the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests Statement\u003c/strong\u003e: A patent application has been filed for this work.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHess, W. T., Hydrogen Peroxide. In \u003cem\u003eKirk-Othmer Encyclopedia of Chemical Technology\u003c/em\u003e, 2000.\u003c/li\u003e\n\u003cli\u003eCampos‐Martin, J. M.; Blanco‐Brieva, G.; Fierro, J. L., Hydrogen peroxide synthesis: an outlook beyond the anthraquinone process. \u003cem\u003eAngewandte Chemie International Edition \u003c/em\u003e\u003cstrong\u003e2006,\u003c/strong\u003e \u003cem\u003e45\u003c/em\u003e (42), 6962-6984.\u003c/li\u003e\n\u003cli\u003ePerry, S. C.; Pangotra, D.;\u0026nbsp; Vieira, L.;\u0026nbsp; Csepei, L.-I.;\u0026nbsp; Sieber, V.;\u0026nbsp; Wang, L.;\u0026nbsp; Ponce de Le\u0026oacute;n, C.; Walsh, F. C., Electrochemical synthesis of hydrogen peroxide from water and oxygen. \u003cem\u003eNat. Rev. Chem. \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e3\u003c/em\u003e (7), 442-458.\u003c/li\u003e\n\u003cli\u003eEdwards, J. K.; Solsona, B.;\u0026nbsp; N, E. N.;\u0026nbsp; Carley, A. F.;\u0026nbsp; Herzing, A. A.;\u0026nbsp; Kiely, C. J.; Hutchings, G. J., Switching off hydrogen peroxide hydrogenation in the direct synthesis process. \u003cem\u003eScience \u003c/em\u003e\u003cstrong\u003e2009,\u003c/strong\u003e \u003cem\u003e323\u003c/em\u003e (5917), 1037-1041.\u003c/li\u003e\n\u003cli\u003eSiahrostami, S.; Verdaguer-Casadevall, A.;\u0026nbsp; Karamad, M.;\u0026nbsp; Deiana, D.;\u0026nbsp; Malacrida, P.;\u0026nbsp; Wickman, B.;\u0026nbsp; Escudero-Escribano, M.;\u0026nbsp; Paoli, E. A.;\u0026nbsp; Frydendal, R.;\u0026nbsp; Hansen, T. W.;\u0026nbsp; Chorkendorff, I.;\u0026nbsp; Stephens, I. E.; Rossmeisl, J., Enabling direct H2O2 production through rational electrocatalyst design. \u003cem\u003eNat. Mater. \u003c/em\u003e\u003cstrong\u003e2013,\u003c/strong\u003e \u003cem\u003e12\u003c/em\u003e (12), 1137-43.\u003c/li\u003e\n\u003cli\u003eZhu, Q.; Hinkle, M.;\u0026nbsp; Kim, D. J.; Kim, J.-H., Modular hydrogen peroxide electrosynthesis cell with anthraquinone-modified polyaniline electrocatalyst. \u003cem\u003eACS ES\u0026amp;T Engineering \u003c/em\u003e\u003cstrong\u003e2020,\u003c/strong\u003e \u003cem\u003e1\u003c/em\u003e (3), 446-455.\u003c/li\u003e\n\u003cli\u003eFreakley, S. J.; He, Q.;\u0026nbsp; Harrhy, J. H.;\u0026nbsp; Lu, L.;\u0026nbsp; Crole, D. A.;\u0026nbsp; Morgan, D. J.;\u0026nbsp; Ntainjua, E. N.;\u0026nbsp; Edwards, J. K.;\u0026nbsp; Carley, A. F.;\u0026nbsp; Borisevich, A. Y.; Hutchings, G. J., Palladium-tin catalysts for the direct synthesis of H2O2 with high selectivity. \u003cem\u003eScience \u003c/em\u003e\u003cstrong\u003e2016,\u003c/strong\u003e \u003cem\u003e351\u003c/em\u003e (6276), 965-968.\u003c/li\u003e\n\u003cli\u003eZhang, X.; Xia, Y.;\u0026nbsp; Xia, C.; Wang, Haotian., Insights into practical-scale electrochemical H2O2 synthesis. \u003cem\u003eTrends in Chemistry \u003c/em\u003e\u003cstrong\u003e2020,\u003c/strong\u003e \u003cem\u003e2\u003c/em\u003e (10), 942-953.\u003c/li\u003e\n\u003cli\u003eYamanaka, I.; Onizawa, T.;\u0026nbsp; Takenaka, S.; Otsuka, K., Direct and continuous production of hydrogen peroxide with 93% selectivity using a fuel‐cell system. \u003cem\u003eAngew. Chem. \u003c/em\u003e\u003cstrong\u003e2003,\u003c/strong\u003e \u003cem\u003e115\u003c/em\u003e (31), 3781-3783.\u003c/li\u003e\n\u003cli\u003eYamanaka, I.; Murayama, T., Neutral H2O2 synthesis by electrolysis of water and O2. \u003cem\u003eAngew. Chem. \u003c/em\u003e\u003cstrong\u003e2008,\u003c/strong\u003e \u003cem\u003e120\u003c/em\u003e (10), 1926-1928.\u003c/li\u003e\n\u003cli\u003eHuang, A.; Delima, R. S.;\u0026nbsp; Kim, Y.;\u0026nbsp; Lees, E. W.;\u0026nbsp; Parlane, F. G.;\u0026nbsp; Dvorak, D. J.;\u0026nbsp; Rooney, M. B.;\u0026nbsp; Jansonius, R. P.;\u0026nbsp; Fink, A. G.;\u0026nbsp; Zhang, Z.; Berlinguette, Curtis. P., Direct H2O2 synthesis, without H2 gas. \u003cem\u003eJ. Am. Chem. Soc. \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e144\u003c/em\u003e (32), 14548-14554.\u003c/li\u003e\n\u003cli\u003eXia, C.; Xia, Y.;\u0026nbsp; Zhu, P.;\u0026nbsp; Fan, L.; Wang, Haotian., Direct electrosynthesis of pure aqueous H2O2 solutions up to 20% by weight using a solid electrolyte. \u003cem\u003eScience \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e366\u003c/em\u003e (6462), 226-231.\u003c/li\u003e\n\u003cli\u003eZhang, X.; Zhao, X.;\u0026nbsp; Zhu, P.;\u0026nbsp; Adler, Z.;\u0026nbsp; Wu, Z.-Y.;\u0026nbsp; Liu, Y.; Wang, Haotian., Electrochemical oxygen reduction to hydrogen peroxide at practical rates in strong acidic media. \u003cem\u003eNat. Commun. \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e13\u003c/em\u003e (1), 2880.\u003c/li\u003e\n\u003cli\u003eXia, Y.; Zhao, X.;\u0026nbsp; Xia, C.;\u0026nbsp; Wu, Z.-Y.;\u0026nbsp; Zhu, P.;\u0026nbsp; Kim, J. Y.;\u0026nbsp; Bai, X.;\u0026nbsp; Gao, G.;\u0026nbsp; Hu, Y.;\u0026nbsp; Zhong, J.; Wang, Haotian., Highly active and selective oxygen reduction to H2O2 on boron-doped carbon for high production rates. \u003cem\u003eNat. Commun. \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e12\u003c/em\u003e (1), 4225.\u003c/li\u003e\n\u003cli\u003ePreger, Y.; Gerken, J. B.;\u0026nbsp; Biswas, S.;\u0026nbsp; Anson, C. W.;\u0026nbsp; Johnson, M. R.;\u0026nbsp; Root, T. W.; Stahl, S. S., Quinone-mediated electrochemical O2 reduction accessing high power density with an off-electrode Co-N/C catalyst. \u003cem\u003eJoule \u003c/em\u003e\u003cstrong\u003e2018,\u003c/strong\u003e \u003cem\u003e2\u003c/em\u003e (12), 2722-2731.\u003c/li\u003e\n\u003cli\u003eTwilton, J.; Johnson, M. R.;\u0026nbsp; Sidana, V.;\u0026nbsp; Franke, M. C.;\u0026nbsp; Bottecchia, C.;\u0026nbsp; Lehnherr, D.;\u0026nbsp; L\u0026eacute;vesque, F.;\u0026nbsp; Knapp, S. M.;\u0026nbsp; Wang, L.;\u0026nbsp; Gerken, J. B.; Stahl, S. S., Quinone-mediated hydrogen anode for non-aqueous reductive electrosynthesis. \u003cem\u003eNature \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e623\u003c/em\u003e (7985), 71-76.\u003c/li\u003e\n\u003cli\u003eMurray, A. T.; Voskian, S.;\u0026nbsp; Schreier, M.;\u0026nbsp; Hatton, T. A.; Surendranath, Yogesh., Electrosynthesis of hydrogen peroxide by phase-transfer catalysis. \u003cem\u003eJoule \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e3\u003c/em\u003e (12), 2942-2954.\u003c/li\u003e\n\u003cli\u003eHuissoud, A.; Tissot, P., Electrochemical reduction of 2-ethyl-9, 10-anthraquinone (EAQ) and mediated formation of hydrogen peroxide in a two-phase medium Part II: Production of alkaline hydrogen peroxide by the intermediate electroreduction of EAQ in a flow-by porous electrode in two-phase liquid\u0026ndash;liquid flow. \u003cem\u003eJ. Appl. Electrochem. \u003c/em\u003e\u003cstrong\u003e1999,\u003c/strong\u003e \u003cem\u003e29\u003c/em\u003e, 17-25.\u003c/li\u003e\n\u003cli\u003eFink, A. G.; Delima, R. S.;\u0026nbsp; Rousseau, A. R.;\u0026nbsp; Hunt, C.;\u0026nbsp; LeSage, N. E.;\u0026nbsp; Huang, A.;\u0026nbsp; Stolar, M.; Berlinguette, Curtis. P., Indirect H2O2 synthesis without H2. \u003cem\u003eNat. Commun. \u003c/em\u003e\u003cstrong\u003e2024,\u003c/strong\u003e \u003cem\u003e15\u003c/em\u003e (1), 766.\u003c/li\u003e\n\u003cli\u003eTang, J.; Zhao, T.;\u0026nbsp; Solanki, D.;\u0026nbsp; Miao, X.;\u0026nbsp; Zhou, W.; Hu, Shu., Selective hydrogen peroxide conversion tailored by surface, interface, and device engineering. \u003cem\u003eJoule \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e5\u003c/em\u003e (6), 1432-1461.\u003c/li\u003e\n\u003cli\u003eJi, Y.; Goulet, M. A.;\u0026nbsp; Pollack, D. A.;\u0026nbsp; Kwabi, D. G.;\u0026nbsp; Jin, S.;\u0026nbsp; Porcellinis, D.;\u0026nbsp; Kerr, E. F.;\u0026nbsp; Gordon, R. G.; Aziz, M. J., A Phosphonate‐Functionalized Quinone Redox Flow Battery at Near‐Neutral pH with Record Capacity Retention Rate. \u003cem\u003eAdv. Energy Mater. \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e9\u003c/em\u003e (12).\u003c/li\u003e\n\u003cli\u003eHuskinson, B.; Marshak, M. P.;\u0026nbsp; Suh, C.;\u0026nbsp; Er, S.;\u0026nbsp; Gerhardt, M. R.;\u0026nbsp; Galvin, C. J.;\u0026nbsp; Chen, X.;\u0026nbsp; Aspuru-Guzik, A.;\u0026nbsp; Gordon, R. G.; Aziz, M. J., A metal-free organic-inorganic aqueous flow battery. \u003cem\u003eNature \u003c/em\u003e\u003cstrong\u003e2014,\u003c/strong\u003e \u003cem\u003e505\u003c/em\u003e (7482), 195-8.\u003c/li\u003e\n\u003cli\u003eFajt, V.; Kurc, L.; Červen\u0026yacute;, L., The effect of solvents on the rate of catalytic hydrogenation of 6‐ethyl‐1,2,3,4‐tetrahydroanthracene‐9,10‐dione. \u003cem\u003eInt. J. Chem. Kinet. \u003c/em\u003e\u003cstrong\u003e2008,\u003c/strong\u003e \u003cem\u003e40\u003c/em\u003e (5), 240-252.\u003c/li\u003e\n\u003cli\u003ePatil, A.; Curtin, D.; Paul, I., Interconversion by hydrogen transfer of unsymmetrically substituted quinhydrones in the solid state. Crystal structure of the 1: 2 complex of 2, 5-dimethylquinone with hydroquinone. \u003cem\u003eJ. Am. Chem. Soc. \u003c/em\u003e\u003cstrong\u003e1984,\u003c/strong\u003e \u003cem\u003e106\u003c/em\u003e (14), 4010-4015.\u003c/li\u003e\n\u003cli\u003eMercado, F. V.; Fern\u0026aacute;ndez, R. A.;\u0026nbsp; Iglesias, R. A.; Dassie, S. A., Facilitated proton transfer reactions via water autoprotolysis across oil| water interfaces. Spectroelectrochemical analysis. \u003cem\u003eElectrochim. Acta \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e299\u003c/em\u003e, 430-440.\u003c/li\u003e\n\u003cli\u003ePatil, A.; Curtin, D.; Paul, I., Solid-state formation of quinhydrones from their components. Use of solid-solid reactions to prepare compounds not accessible from solution. \u003cem\u003eJ. Am. Chem. Soc. \u003c/em\u003e\u003cstrong\u003e1984,\u003c/strong\u003e \u003cem\u003e106\u003c/em\u003e (2), 348-353.\u003c/li\u003e\n\u003cli\u003eGoulet, M. A.; Tong, L.;\u0026nbsp; Pollack, D. A.;\u0026nbsp; Tabor, D. P.;\u0026nbsp; Odom, S. A.;\u0026nbsp; Aspuru-Guzik, A.;\u0026nbsp; Kwan, E. E.;\u0026nbsp; Gordon, R. G.; Aziz, M. J., Extending the Lifetime of Organic Flow Batteries via Redox State Management. \u003cem\u003eJ. Am. Chem. Soc. \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e141\u003c/em\u003e (20), 8014-8019.\u003c/li\u003e\n\u003cli\u003eJing, Y.; Zhao, E. W.;\u0026nbsp; Goulet, M. A.;\u0026nbsp; Bahari, M.;\u0026nbsp; Fell, E. M.;\u0026nbsp; Jin, S.;\u0026nbsp; Davoodi, A.;\u0026nbsp; Jonsson, E.;\u0026nbsp; Wu, M.;\u0026nbsp; Grey, C. P.;\u0026nbsp; Gordon, R. G.; Aziz, M. J., In situ electrochemical recomposition of decomposed redox-active species in aqueous organic flow batteries. \u003cem\u003eNat. Chem. \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e14\u003c/em\u003e (10), 1103-1109.\u003c/li\u003e\n\u003cli\u003eShang, H.; Zhou, H.;\u0026nbsp; Zhang, W.; Zhang, K., Regeneration of working solution in the hydrogen peroxide production process. \u003cem\u003eThe Canadian Journal of Chemical Engineering \u003c/em\u003e\u003cstrong\u003e2011,\u003c/strong\u003e \u003cem\u003e89\u003c/em\u003e (5), 1296-1302.\u003c/li\u003e\n\u003cli\u003eKwabi, D. G.; Lin, K.;\u0026nbsp; Ji, Y.;\u0026nbsp; Kerr, E. F.;\u0026nbsp; Goulet, M.-A.;\u0026nbsp; De Porcellinis, D.;\u0026nbsp; Tabor, D. P.;\u0026nbsp; Pollack, D. A.;\u0026nbsp; Aspuru-Guzik, A.;\u0026nbsp; Gordon, R. G.; Aziz, M. J., Alkaline Quinone Flow Battery with Long Lifetime at pH 12. \u003cem\u003eJoule \u003c/em\u003e\u003cstrong\u003e2018,\u003c/strong\u003e \u003cem\u003e2\u003c/em\u003e (9), 1894-1906.\u003c/li\u003e\n\u003cli\u003eLu, S.; Wang, L.;\u0026nbsp; Wang, Y.; Mi, Z., Kinetic Model of Gas‐Liquid‐Liquid Reactive Extraction for Production of Hydrogen Peroxide. \u003cem\u003eChem. Eng. Technol. \u003c/em\u003e\u003cstrong\u003e2011,\u003c/strong\u003e \u003cem\u003e34\u003c/em\u003e (5), 823-830.\u003c/li\u003e\n\u003cli\u003eLi, T.; Lees, E. W.;\u0026nbsp; Goldman, M.;\u0026nbsp; Salvatore, D. A.;\u0026nbsp; Weekes, D. M.; Berlinguette, C. P., Electrolytic conversion of bicarbonate into CO in a flow cell. \u003cem\u003eJoule \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e3\u003c/em\u003e (6), 1487-1497.\u003c/li\u003e\n\u003cli\u003eWu, Z.-Y.; Chen, F.-Y.;\u0026nbsp; Li, B.;\u0026nbsp; Yu, S.-W.;\u0026nbsp; Finfrock, Y. Z.;\u0026nbsp; Meira, D. M.;\u0026nbsp; Yan, Q.-Q.;\u0026nbsp; Zhu, P.;\u0026nbsp; Chen, M.-X.; Song, T.-W., Non-iridium-based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane water electrolysis. \u003cem\u003eNat. Mater. \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e22\u003c/em\u003e (1), 100-108.\u003c/li\u003e\n\u003cli\u003eOener, S. Z.; Foster, M. J.; Boettcher, S. W., Accelerating water dissociation in bipolar membranes and for electrocatalysis. \u003cem\u003eScience \u003c/em\u003e\u003cstrong\u003e2020,\u003c/strong\u003e \u003cem\u003e369\u003c/em\u003e (6507), 1099-1103.\u003c/li\u003e\n\u003cli\u003eKerr, E. F.; Tang, Z.;\u0026nbsp; George, T. Y.;\u0026nbsp; Jin, S.;\u0026nbsp; Fell, E. M.;\u0026nbsp; Amini, K.;\u0026nbsp; Jing, Y.;\u0026nbsp; Wu, M.;\u0026nbsp; Gordon, R. G.; Aziz, M. J., High energy density aqueous flow battery utilizing extremely stable, branching-induced high-solubility anthraquinone near neutral pH. \u003cem\u003eACS Energy Lett. \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e8\u003c/em\u003e (1), 600-607.\u003c/li\u003e\n\u003cli\u003eKurc, L.; P\u0026aacute;ter, M.; Červen\u0026yacute;, L., Activity of basic catalysts in oxidation of 2-ethyl-5,6,7,8-tetrahydro-9,10-anthrahydroquinone. \u003cem\u003eJ. Mol. Catal. A: Chem. \u003c/em\u003e\u003cstrong\u003e2003,\u003c/strong\u003e \u003cem\u003e202\u003c/em\u003e (1-2), 327-332.\u003c/li\u003e\n\u003cli\u003eOsakai, T.; Okamoto, M.;\u0026nbsp; Sugihara, T.; Nakatani, K., Bimolecular-reaction effect on the rate constant of electron transfer at the oil/water interface as studied by scanning electrochemical microscopy. \u003cem\u003eJ. Electroanal. Chem. \u003c/em\u003e\u003cstrong\u003e2009,\u003c/strong\u003e \u003cem\u003e628\u003c/em\u003e (1-2), 27-34.\u003c/li\u003e\n\u003cli\u003eCukier, R. I.; Nocera, Daniel. G., Proton-coupled electron transfer. \u003cem\u003eAnnu. Rev. Phys. Chem. \u003c/em\u003e\u003cstrong\u003e1998,\u003c/strong\u003e \u003cem\u003e49\u003c/em\u003e (1), 337-369.\u003c/li\u003e\n\u003cli\u003eXia, C.; Zhu, P.;\u0026nbsp; Jiang, Q.;\u0026nbsp; Pan, Y.;\u0026nbsp; Liang, W.;\u0026nbsp; Stavitski, E.;\u0026nbsp; Alshareef, H. N.; Wang, Haotian., Continuous production of pure liquid fuel solutions via electrocatalytic CO2 reduction using solid-electrolyte devices. \u003cem\u003eNat. Energy \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e4\u003c/em\u003e (9), 776-785.\u003c/li\u003e\n\u003cli\u003eSherbo, R. S.; Delima, R. S.;\u0026nbsp; Chiykowski, V. A.;\u0026nbsp; MacLeod, B. P.; Berlinguette, C. P., Complete electron economy by pairing electrolysis with hydrogenation. \u003cem\u003eNat. Catal. \u003c/em\u003e\u003cstrong\u003e2018,\u003c/strong\u003e \u003cem\u003e1\u003c/em\u003e (7), 501-507.\u003c/li\u003e\n\u003cli\u003eLewis, R. J.; Hutchings, G. J., Selective oxidation using In situ-generated hydrogen peroxide. \u003cem\u003eAcc. Chem. Res. \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e57\u003c/em\u003e (1), 106-119.\u003c/li\u003e\n\u003cli\u003eChanda, A.; Fokin, V. V., Organic synthesis \u0026ldquo;on water\u0026rdquo;. \u003cem\u003eChem. Rev. \u003c/em\u003e\u003cstrong\u003e2009,\u003c/strong\u003e \u003cem\u003e109\u003c/em\u003e (2), 725-748.\u003c/li\u003e\n\u003cli\u003eShang, H.; Chen, Y.;\u0026nbsp; Guan, S.;\u0026nbsp; Wang, Y.;\u0026nbsp; Cao, J.;\u0026nbsp; Wang, X.;\u0026nbsp; Li, H.; Bian, Z., Scalable and selective gold recovery from end-of-life electronics. \u003cem\u003eNature Chemical Engineering \u003c/em\u003e\u003cstrong\u003e2024,\u003c/strong\u003e \u003cem\u003e1\u003c/em\u003e (2), 170-179.\u003c/li\u003e\n\u003cli\u003eXu, Y.; Mao, Z.;\u0026nbsp; Qu, R.;\u0026nbsp; Wang, J.;\u0026nbsp; Yu, J.;\u0026nbsp; Luo, X.;\u0026nbsp; Shi, M.;\u0026nbsp; Mao, X.;\u0026nbsp; Ding, J.; Liu, B., Electrochemical hydrogenation of oxidized contaminants for water purification without supporting electrolyte. \u003cem\u003eNature Water \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e1\u003c/em\u003e (1), 95-103.\u003c/li\u003e\n\u003cli\u003eWillner, I., Photoinduced electron transfer across a water-oil boundary: A model for redox reaction separation. \u003cstrong\u003e1979\u003c/strong\u003e.\u003c/li\u003e\n\u003cli\u003eHan, C.; Zenner, J.;\u0026nbsp; Johny, J.;\u0026nbsp; Kaeffer, N.;\u0026nbsp; Bordet, A.; Leitner, W., Electrocatalytic hydrogenation of alkenes with Pd/carbon nanotubes at an oil\u0026ndash;water interface. \u003cem\u003eNat. Catal. \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e5\u003c/em\u003e (12), 1110-1119.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4986886/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4986886/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) is predominantly produced via the centralized thermocatalytic hydrogenation-anthraquinone oxidation (t-AO) process, a conventional nonaqueous method. Electrifying such nonaqueous processes with improved selectivity remains a significant challenge. Here, we present a multi-phase electrochemical anthraquinone autoxidation (e-AO) system that leverages an interfacial hydrogen atom transfer reaction facilitated by a heterogeneous molecular catalytic process. This design enables aqueous electrochemical reactions with over 97% efficiency at high current densities (\u0026gt; 200 mA cm\u003csup\u003e−2\u003c/sup\u003e), using only carbon electrodes. The aqueous-nonaqueous interfacial hydrogen atom transfer, operating with nearly 100% selectivity through a quinhydrone intermediate, eliminates waste caused by over-reduction of anthraquinones in conventional t-AO processes. Our approach combines the benefits of aqueous electrochemistry with those of the traditional t-AO process while addressing issues like unwanted electrolyte migration in aqueous systems and anthraquinone over-reduction in t-AO. This strategy enables the continuous production of low-cost, high-purity H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions (\u0026gt; 10 wt.%) and promotes the electrification and decentralization of nonaqueous chemical processes.\u003c/p\u003e","manuscriptTitle":"Electrifying Industrial Hydrogen Peroxide Production via Interfacial Molecular Mediation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-09-13 06:24:11","doi":"10.21203/rs.3.rs-4986886/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-chemistry","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nchem","sideBox":"Learn more about [Nature Chemistry](http://www.nature.com/nchem/)","snPcode":"","submissionUrl":"","title":"Nature Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"94fcb5bb-a2e6-4552-82ca-cd6bb3a086f5","owner":[],"postedDate":"September 13th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":37470467,"name":"Physical sciences/Chemistry/Electrochemistry"},{"id":37470468,"name":"Physical sciences/Chemistry/Chemical synthesis/Flow chemistry"},{"id":37470469,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"},{"id":37470470,"name":"Physical sciences/Chemistry/Organic chemistry/Synthetic chemistry methodology"},{"id":37470471,"name":"Physical sciences/Engineering/Chemical engineering"}],"tags":[],"updatedAt":"2025-09-23T07:09:10+00:00","versionOfRecord":{"articleIdentity":"rs-4986886","link":"https://doi.org/10.1038/s41557-025-01940-7","journal":{"identity":"nature-chemistry","isVorOnly":false,"title":"Nature Chemistry"},"publishedOn":"2025-09-22 04:00:00","publishedOnDateReadable":"September 22nd, 2025"},"versionCreatedAt":"2024-09-13 06:24:11","video":"","vorDoi":"10.1038/s41557-025-01940-7","vorDoiUrl":"https://doi.org/10.1038/s41557-025-01940-7","workflowStages":[]},"version":"v1","identity":"rs-4986886","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4986886","identity":"rs-4986886","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}