Electrosynthesis of hydrogen peroxide with anion exchange membrane-free resin wafer reactors

Electrosynthesis of hydrogen peroxide with anion exchange membrane-free resin wafer reactors | 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 Electrosynthesis of hydrogen peroxide with anion exchange membrane-free resin wafer reactors Yujue Wang, Chaoyong Sun, Jiaqiang Zhong, Erzhuo Zhao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7636698/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Porous solid electrolyte (PSE) reactors have attracted worldwide interest in H 2 O 2 electrosynthesis and other electrochemical processes (e.g., CO 2 reduction). However, scaling up PSE reactors for industrial applications faces several challenges, including the difficulty in uniformly packing PSE (typically resin microspheres) in large reactors, the high pressure drop across the reactor, and the limited durability of anion exchange membranes (AEM). Here, to address these challenges, we fabricated robust PSE wafers with both high ion conductivity and porosity by pre-molding resin microspheres, conductive binder, and pore-forming agent. These pre-molded wafers can be easily installed in reactors, thereby simplifying the reactor assembly and scalability. Moreover, due to their high porosity, the PSE wafers dramatically reduced the pressure drops across the reactor by a factor of ~ 5–7 compared to resin microsphere-packed beds. Consequently, the wafer reactors could be stably operated without the need of an AEM for preventing electrode flooding, circumventing the barrier to long-term stability of PSE reactors. By addressing these bottlenecks, the wafer reactor provide a robust and scalable platform for practical H 2 O 2 electrosynthesis. Physical sciences/Engineering/Chemical engineering Physical sciences/Materials science/Materials for energy and catalysis/Electrocatalysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The development of porous solid electrolyte (PSE) electrochemical reactors marks a significant advancement in the electrochemical synthesis of hydrogen peroxide (H 2 O 2 ) (Xia et al., 2019). Unlike conventional reactors that rely on aqueous electrolytes such as potassium hydroxide (KOH) and sodium sulfate (Na 2 SO 4 ), PSE reactors utilize ion-conducting solids (typically ion-exchange resin microspheres) as the electrolyte medium between the anode and cathode (Kim et al., 2022; Chen et al., 2024). This innovative design enables the direct electrosynthesis of H 2 O 2 in pure water, yielding electrolyte-free H 2 O 2 solutions that can be directly used in various application (e.g., disinfection and environmental remediation) without the need for downstream purification (Deng et al., 2024; Mazzucato et al., 2024). By eliminating liquid electrolytes and associated downstream separation steps, PSE reactors reduce process complexity and operating costs, thereby enhancing their commercial competitiveness (Wen et al., 2022; Shin et al., 2023; Chen et al., 2025). These benefits have generated worldwide interest in the PSE technology, not only for H 2 O 2 electrosynthesis, but also for other electrochemical processes, such as carbon dioxide reduction and lithium ion recovery (Li et al., 2024; Elgazzar and Wang, 2025; Fang et al., 2025; Liu et al., 2025). Despite their promise, scaling up PSE reactors for industrial applications faces several engineering challenges (Elgazzar and Wang, 2025; Zhao et al., 2025). As illustrated in Fig. 1a, a typical PSE reactor comprises three chambers: an anode chamber, a gas diffusion electrode (GDE) cathode chamber, and a middle PSE chamber densely packed with ion-exchange resin microspheres (Xia et al., 2019). However, achieving uniform packing of resin microspheres becomes increasingly difficult as reactor size increases (Elgazzar and Wang, 2025; Zhao et al., 2025), and even minor nonuniformities in the packing can cause local resistance variations, thus leading to uneven flow field distribution, increased cell voltages, and reduced Faradaic efficiencies (FEs) (Xia et al., 2019; Lin et al., 2025; Zhao et al., 2025). Moreover, efficient ion transport requires small-diameter resin microspheres packed tightly to maximize interparticle contact (Elgazzar and Wang, 2025; Zhao et al., 2025). However, such dense packing of microspheres results in low porosity (ε) and thus high pressure drops across the microsphere-packed bed. Consequently, high pumping pressures are required to pass water through the PSE reactor to extract synthesized H 2 O 2 (Zhao et al., 2025). The high pressures not only increase energy consumption, but more critically, pose challenges to the stability of the reactor (Elgazzar and Wang, 2025; Zhao et al., 2025). For example, due to the high water pressures, an anion exchange membrane (AEM) has to be placed between the PSE layer and the GDE cathode to prevent the cathode from being quickly flooded by water, while allowing HO 2 − produced at the cathode to diffuse to the PSE layer (Xia et al., 2019; Zhang et al., 2020; Sabri Rawah et al., 2023; Yi et al., 2025). Unfortunately, the limited mechanical, chemical, and thermal durability of AEMs leads to their gradual degradation during H 2 O 2 electrosynthesis, posing a critical barrier to long-term stability of PSE reactors (Zhang et al., 2020; Qi et al., 2023; Shin et al., 2023; Zhao et al., 2025). To address these challenges, we engineered structured PSE wafers composed of ion-exchange resins, conductive binders, and pore-forming agents, then used them as the integrated PSE layer within the reactor. Compared with uniformly packing resin microspheres between the anode and cathode, these wafers can be easily pre-molded with precise geometry, and then conveniently installed into reactors, thereby simplifying reactor assembly and scalability. More importantly, through systematic optimization of composition and molding parameters, thin, robust PSE wafers with both high ionic conductivity and porosity can be fabricated, thus overcoming the inherent trade-off between ion conductivity and hydraulic resistance observed for microsphere-packed beds. Consequently, the PSE wafer reactor can be operated at significantly lower pressure drops without compromising cell voltages and FEs during H 2 O 2 electrosynthesis as compared to microsphere-packed reactors. Notably, the reduced water pressures eliminate the need for an AEM to prevent cathode flood during H 2 O 2 electrosynthesis, circumventing the barrier to long-term stability of PSE reactors. Overall, by addressing key bottlenecks in reactor assembly, scalability, and stability, PSE wafer reactors provide a robust and scalable platform for practical H 2 O 2 electrosynthesis, paving the way for the industrial deployment of PSE-based technologies. Results Characterizations of PSE wafers Currently, resin microspheres made from sulfonic acid (SA) functionalized styrene-divinylbenzene copolymer are commonly used as the ion conductor in PSE reactors for H 2 O 2 electrosynthesis (Xia et al., 2019; Perry et al., 2021). Based on previous works (Rawah et al., 2023; Fang et al., 2025; Zhao et al., 2025), Dowex 50 W×8 resin microspheres were selected as the PSE conductor in this study because it has a high surface density of SA groups that are favorable for H + conduction during H 2 O 2 electrosynthesis. In the PSE reactor, numerous resin microspheres are densely packed into a thin layer to conduct protons (H + ) from the anode to the cathode along their interconnected surface, while allowing water to flow through their interstitial space to extract produced H 2 O 2 out of the reactor (see Fig. 1a) (Xia et al., 2019). As illustrated in Fig. 2g, H + conduction on the microsphere surface proceeds through a hopping diffusion process between neighboring SA groups (i.e., the Grotthuss mechanism) (Liu et al., 2016; Klumpen et al., 2017), and the rate of H + conduction across the PSE layer is mainly limited by interparticle H + hopping at the contact points of packed microspheres (Zhao et al., 2025). To enhance the interparticle H + conduction, smaller microspheres and higher packing density are desired to increase the contact points among packed microspheres (Zhao et al., 2025). However, while using smaller microspheres or higher packing densities can enhance the interparticle H + conduction and thus reduce the resistance of H + conduction (R s ) of the PSE layer, the porosity (ε) of the layer decreases (see Table 1). This will considerably increase the pressure drop across the layer according to the Kozeny-Carman equation (Eq. 1). where ΔP is the pressure drop across the PSE bed, μ is the viscosity of water, ε is the porosity of the bed, L is total height of the bed, Φ s is the sphericity of microspheres in the packed bed (Φ s = 1 for spherical particles), d p is the diameter of the volume equivalent spherical particle, u is the superficial velocity, Q is the volumetric flow rate of the fluid, and A is the cross-sectional area of the bed perpendicular to the water flow direction. On the other hand, while using larger microspheres or lower packing densities increases the porosity of the layer, the R s of the layer increased (Table 1), which will substantially increase the cell voltage and energy consumption of H 2 O 2 electrosynthesis (Zhao et al., 2025). Therefore, there exists an inherent trade-off between the ion conductivity and porosity of microsphere-packed beds when they are used as the PSE layer in PSE reactors. Table 1. Proton conduction resistance and porosity of resin microsphere-packed beds and resin wafers. PSE Parameters R s (Ω) Porosity (%) Diameter (μm) Packing density (mg/mL) Resin microsphere-packed bed 150–300 800 3.28 36 150–300 1000 2.01 20 150–300 1100 1.77 11 35–75 1200 1.14 4 75–150 1200 1.18 4 300–1000 950 2.43 23 Mixing ratio of resin microspheres (g), NaCl (g), and bind (mL) Resin wafer 5:9:1 1.92 50 7:7:1 1.83 39 9:5:1 1.83 36 Notably, by tuning the mixing ratios of resin microspheres, pore forming agent (sodium chloride particles), and conductive binder (sulfonated polyetheretherketone), the PSE wafers achieved both high ion conductivity and porosity simultaneously (Table 1). As shown in the SEM image (Fig. 1f), the binder filled the interstices of resin microspheres and bound them together. Because the binder can also transport H + through the hopping diffusion process between neighboring surface SA groups, it significantly increases ion-conducting pathways at the contact points of microspheres (Fig. 1k). Therefore, the interparticle H + conduction among resin microspheres is substantially enhanced in the PSE wafer, overcoming the bottleneck of H + conduction across the microsphere-packed bed. Meanwhile, high porosity (e.g., 36%–50%) could be obtained after the pore forming agent (NaCl) embedded in the wafer was dissolved in water (see Fig. 1n). The PSE wafer thus overcomes the trade-off between ion conductivity and porosity as observed for microsphere-packed beds. In addition, PSE wafers can be pre-molded with a precise geometry and uniform thickness, then easily assembled into reactor, which can considerably promote the uniform contact between PSE, membrane, and electrodes (see Fig. 1c and Fig. S1). In comparison, uniformly packing resin microspheres between the anode and cathode is laborious and challenging, especially in large reactors (Zhao et al., 2025), and variations in the packing can result in non-uniform PSE/membrane/electrode contact and thus resistance fluctuations among different experimental runs or PSE reactors (Elgazzar and Wang, 2025). Therefore, we anticipate that compared with resin microsphere-packed beds, PSE wafers can effectively improve the scalability and reproducibility of PSE reactors (see below). H 2 O 2 electrosynthesis with microsphere-packed and wafer reactors The performance of H 2 O 2 electrosynthesis using the microsphere-packed reactor and PSE wafer reactor are compared in Fig. 2 and Fig. S8. For the microsphere-packed reactor, previous studies have shown that PSE layers packed with 150–300 μm resin microspheres and a packing density of ~1100 mg/mL best balance the trade-off between ion conductivity and porosity for efficient and stable H 2 O 2 electrosynthesis (Zhao et al., 2025). The same setting was therefore adopted to assemble the microsphere-packed reactor used in this study. For the wafer reactor, PSE wafers fabricated with a mixing ratio 7 (g):7 (g):1 (mL) of resin microspheres, NaCl particles, and binder were used. As reported in Table 1, the resin wafers achieved a similar H + conductivity (R s = 1.83 Ω) at a significantly higher porosity (ε = 39%) than the microsphere-packed layer (R s = 1.77 Ω, ε = 11%) (Fig. S4). Fig. 2a and Fig. S8a show that under the same operating conditions (identical current densities and flow rates), the wafer reactor produced similar or slightly higher concentrations of H 2 O 2 than the microsphere-packed reactor. Meanwhile, the cell voltage of the wafer reactor was only marginally higher than that of the microsphere-packed reactor (Fig. 2b), possibly due to the slightly higher R s of the wafer. Therefore, the electric energy consumption of H 2 O 2 production are generally comparable for the two reactors (Fig. 2b). In contrast, the pressure drops across the two reactors were significantly different (Fig. 2c). Due to its lower porosity, the pressure drops across the microsphere-packed reactor increased rapidly with increasing flow rates (k = 9.488), reaching ~100 kPa at a flow rate of 10 mL/min. In comparison, the pressure drops across the wafer reactor increased only slowly (k = 2.105) with increasing flow rates. Consequently, the pressure drop across the wafer reactor was only ~20 kPa at the highest flow rate tested in this study. Compared to the microsphere-packed reactor, the wafer reactor can thus dramatically reduce the pumping energy consumption during H 2 O 2 electrosynthesis, especially when high flow rates are applied (see Fig. S10). The results shown above highlight that by addressing the inherent trade-off between ion conductivity and porosity of microsphere-packed reactors, resin wafers can significantly reduce the pressure drop across PSE reactors, while maintaining high FEs and low cell voltages during H 2 O 2 electrosynthesis. In contrast, while decreasing the packing density or increasing the particle size of resin microspheres could also increase the porosity of microsphere-packed beds and thus reduce the pressure drop across the reactor, the H + conductivity of the bed decreased considerably, thereby resulting in substantially higher cell voltages and electric energy consumption of H 2 O 2 production (see Fig. S5 for more detail). Due to the high pressure drop across the microsphere-packed reactor, an AEM had to be placed between the PSE bed and the GDE cathode to prevent electrode flooding during H 2 O 2 electrosynthesis (Xia et al., 2019; Zhao et al., 2025). Otherwise, the performance of the microsphere-packed reactor deteriorated quickly in only a few hours due to the electrode flooding (see Fig. 2d). While the use of AEM improved the operational stability of microsphere-packed reactors, the AEM would retain some of the produced H 2 O 2 at the cathode/AEM interface, resulting in over-reduction of H 2 O 2 to H 2 O (Shin et al., 2023; Xia et al., 2025). This effect is more significant when low water flow rates are applied to produce high-concentration H 2 O 2 solutions (Xia et al., 2025), thereby causing the lower H 2 O 2 concentrations and FEs of the microsphere-packed reactor than the wafer reactor at flow rates lower than 5.21 mL/min (see Fig. 2a). Moreover, the AEM introduces additional ohmic resistance and will thus increase cell voltages in the microsphere-packed reactor (Shin et al., 2023). More critically, AEMs are susceptible to gradual degradation due to mechanical stress, thermal effects, and chemical reactions during H 2 O 2 electrosynthesis (Rawah et al., 2023; Xia et al., 2025; Zhao et al., 2025). Consequently, the performance of microsphere-packed reactor declined progressively after ~76 h (Fig. 2d), primarily due to the increasing electrode flooding as the AEM was gradually degraded (see Fig. S7 for more information). In contrast to the microsphere-packed reactor, the reduced water pressures allow the wafer reactor to be stably operated without using an AEM to separate the GDE and PSE layer. As shown in Fig. 2d, the wafer reactor operated stably during the long-term evaluation, and no electrode flood was observed at the end of the test. The wafer reactor can thus avoid the efficiency and long-term stability problems associated with the use of AEM for H 2 O 2 electrosynthesis. Scalability evaluation To evaluate the scalability of microsphere-packed and wafer reactors, we increased the electrode area from 4 cm 2 (2 cm × 2 cm) to 25 cm 2 (5 cm × 5 cm), and then tested the enlarged reactors for H 2 O 2 electrosynthesis. Compared with their smaller counterparts, the two enlarged reactors increased the concentration of synthesized H 2 O 2 solutions by 5.9–6.4 times under the same operating conditions (Figs. 3a). These increases are almost the same as the increase of electrode area (6.25 times), indicating that there are no significant changes in FEs of H 2 O 2 production during the reactor scaling up (Fig. 3a and Fig. S9a). Meanwhile, the cell voltages increased only moderately for the enlarged reactors than the smaller reactors (Fig. 3b and Fig. S9b), possibly due to the uneven current distribution and mass transfer as the electrode size increases (Martinez-Huitle et al., 2015; An et al., 2022; Cui et al., 2024). Therefore, the electric energy consumption of H 2 O 2 production increased only modestly for the enlarged reactors compared to their smaller counterparts (Fig. 3b). Note that during the reactor enlargement, both the height (L) and the cross-sectional area perpendicular to the water flow (A) of the microsphere-packed bed or wafer increased by the same factor (2.5 times), which will effectively balance their influences on pressure drop according to the Kozeny-Carman equation (Eq. 1). Therefore, it is expected that for the same flow rate, the pressure drops through the smaller and enlarged reactors will not change considerably. Consistent with the theoretical prediction, the pressure drops across the enlarged wafer reactor remained almost the same as its smaller counterpart during H 2 O 2 electrosynthesis (Figs. 2c and 3c). However, the pressure drops across the enlarged microsphere-packed reactor increased by ~10–15 kPa than its smaller counterpart during most experiments. These increases are possibly caused by slight variations in the packing of resin microspheres, which is difficult to control in large reactors (Elgazzar and Wang, 2025; Zhao et al., 2025). In comparison, the properties of PSE wafers (e.g., geometry, ion conductivity, and porosity) can be more precisely and uniformly controlled during fabrication. Therefore, the performance of wafer reactors is more reproducible, which is important for reactor scaling up and practical applications. With current densities of 100–150 mA/cm 2 , the enlarged wafer reactor produced up to ~16200–21000 mg/L (1.62–2.10 wt%) H 2 O 2 at a flow rate of 1.58 mL/min in the continuous flow mode (see Fig. 3a and SI Fig. S9a). To further increase the concentrations of H 2 O 2 solutions, the product stream can be recirculated through the reactor (or passing consecutively through reactor stacks) until desired H 2 O 2 concentrations are reached (see Fig. 4a for the operation scheme) (Ruggiero et al., 2024; Xia et al., 2025). Fig. 4b shows that as the product stream was recirculated through the wafer reactor, H 2 O 2 concentrations increased to ~11 wt% after 90 min operation, while maintaining a high FE of H 2 O 2 production of ~92%. In comparison, FEs decreased gradually during H 2 O 2 electrosynthesis with the microsphere-packed reactor, possibly due to the enhanced H 2 O 2 decomposition at the cathode/AEM interface as H 2 O 2 concentrations increase (Deng et al., 2024; Xia et al., 2025; Zhang et al., 2025). As a result, a lower H 2 O 2 concentration (9.25 wt%) and FE (77%) was obtained at the end of H 2 O 2 electrosynthesis with the microsphere-packed reactor. Note that during the recirculation operation, a relatively high water flow rate of 5.2 mL/min was applied to enhance the transport of the generated H 2 O 2 away from the cathode surface, and thus to minimize its further reduction (Ruggiero et al., 2024; Xia et al., 2025). Nevertheless, it seems that this approach is less effective for the microsphere-packed reactor because of the separation of the cathode and water stream by the AEM. Fig. 4c show that during the recirculation operation, cell voltages increased gradually for the microsphere-packed reactor, but were generally stable for the wafer reactor. The increases of cell voltages can be mainly attributed to the generation and accumulation of gas bubbles in the reactors during H 2 O 2 electrosynthesis (Zhao et al., 2023; Elgazzar and Wang, 2025). As H 2 O 2 concentrations increase during the recirculation operation, self- and thermal decomposition of H 2 O 2 is enhanced in the reactor, which can generate some oxygen gas bubbles in the PSE layer. Due to the lower porosity of microsphere-packed beds, the bubbles are less effectively removed from the microsphere-packed reactor by the passing water stream than from the wafer reactor. Consequently, more gas bubbles accumulated in the microsphere-packed reactor, which would disrupt ion conduction and thus result in higher cell voltages (Kim et al., 2020; Lazaridis et al., 2022; Elgazzar and Wang, 2025). Based on the FEs and cell voltages observed during H 2 O 2 electrosynthesis, the electrical energy consumption of H 2 O 2 production are calculated using Eq. 3. Due to the decreases of FEs and increases of cell voltages, the energy consumption increased during H 2 O 2 electrosynthesis with the microsphere-packed reactor (Fig. 4c). When a 9.25 wt% H 2 O 2 solution was obtained, the energy consumption is 9.23 kWh/kg H 2 O 2 (on a 100 wt% basis). This value is about the same as that reported for microsphere-packed reactors tested under similar experimental conditions in a recent study (~11.3 kWh/kg H 2 O 2 for 10 wt% H 2 O 2 solutions, see SI Table S1 for more detail) (Xia et al., 2025). In comparison, energy consumption remained relatively stable at ~6 kWh/kg H 2 O 2 during H 2 O 2 electrosynthesis with the wafer reactor because of the insignificant changes of FEs and cell voltages. In addition, compared with conventional reactors using aqueous electrolytes, the resin wafer reactor demonstrated generally higher FEs when producing H 2 O 2 solutions of the same concentrations (see Table S1). These findings underscore the potential of the wafer reactor as a more energy-efficient alternative to conventional reactors, in addition to the benefit of avoiding the cost associated with aqueous electrolytes and downstream separation, which can substantially increase operational expenses (Cao et al., 2021; Zhao et al., 2023). Conclusions In summary, we have developed robust PSE wafers with both high ionic conductivity and porosity to address key engineering challenges faced by current PSE reactors that use resin microsphere-packed beds as the PSE layer for H 2 O 2 electrosynthesis. Because of their higher porosity, the PSE wafers dramatically reduced the pressure drops across the reactor during H 2 O 2 electrosynthesis compared to resin microsphere-packed reactors. This improvement enables stable operation of the wafer reactors without the need for an AEM to mitigate GDE flooding during H 2 O 2 electrosynthesis, thereby circumventing a critical barrier to long-term stability of PSE reactors associated with AEM use. Additionally, the high conductivity of PSE wafers facilitates efficient H 2 O 2 production with high FEs and low energy consumption. Furthermore, the molding process employed for wafer fabrication ensures precise geometry and high uniformity, which substantially improve the assembly, scalability, and reproducibility of PSE reactors. Overall, by addressing the key limitations of resin microsphere-packed beds, the PSE wafer significantly enhance the feasibility of PSE reactors for practical H 2 O 2 electrosynthesis, as well as other electrochemical processes such as CO 2 reduction. Methods Materials and chemicals Resin microspheres (150–300 µm), NaCl (99%), N,N-Dimethylformamide (DMF, 99.5%) anhydrous ethanol (99.8%) were purchased from Sigma-Aldrich. Sulfonated polyetheretherketone (SPEEK, 60% sulfonated) was purchased from Zhongheng New Materials Technology Co., LTD. Hydrophobic GDL carbon paper (HCP135, Hesen Co., Ltd., China), IrO 2 (Accelerate®), black carbon (BP2000), Nafion-115 membrane (PEM), nafion solution (D520, 5wt.%) and sustainion X37-50 Grade RT membrane (AEM) were purchased from SCI Materials Hub. Alkymer anion exchange resin binder solution (I-250, 5wt.%) was purchased from EVE Hydrogen Energy Co., LTD. All experiments used Millipore water (18.2 MΩ cm − 1 ). Fabrication of PSE wafers To fabricate resin wafers, appropriate amounts of resin microspheres, NaCl crystals, and binder (SPEEK dissolved in DMF with 15% mass fraction) were uniformly mixed in a mortar. The mixture was then transferred into the cavity of stainless steel molds and pressed with a pressure of 10 kPa at room temperature for 12 h. After the molding process, the obtained PSE wafers were washed with deionized water to dissolve NaCl particles embedded in the matrix, then dried at 70 ℃ for 24 h prior to installation into PSE reactors. The ion conductivity and porosity of the wafers can be adjusted by varying the mixing ratios of resin microspheres, NaCl, and binder. Preparation of GDE cathode and IrO 2 anode Nine milligrams of carbon black (BP2000), 90 µL of alkymer anion exchange resin binder solution (I-250, 5 wt%), and 10 mL of 75% ethanol were mixed in an ultrasonic bath for 30 min. The obtained homogeneous ink was then sprayed onto a 3 cm × 3 cm carbon paper (HCP 135) at 40°C. Next, the carbon paper was naturally dried at room temperature for 24 h to prepare GDE cathodes for PSE reactors. To prepare the anode, IrO 2 (4.5 mg) and Nafion solution (40 µL, D520, 5wt.%) were dispersed into 5 ml of ethanol under ultrasonication. After 30 min ultrasonication, the as-prepared ink was then sprayed onto a 3 cm × 3 cm Nafion-115 membrane at 70°C to prepare the catalyst-coated membrane (CCM) anode used in PSE reactors. PSE reactor configurations and HO electrosynthesis The configurations of resin microsphere-packed reactor and wafer reactor are shown in Figs. 1 b and c. Both reactors had an IrO 2 anode and GDE cathode for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), respectively. In the microsphere-packed reactor, the anode and cathode sandwiched a PEM (Nafion-115), a layer of densely packed resin microspheres (thickness of 2 mm), and an AEM (sustainion X37-50). In comparison, the anode and cathode in the wafer reactor sandwiched a PEM and a pre-molded resin wafer, without using an AEM to separate the wafer and the cathode. During H 2 O 2 electrosynthesis experiments, an oxygen gas (50 mL/min) was fed through the cathode chamber to provide oxygen for ORR, while a DI water stream was passed through the middle PSE chamber using a peristaltic pump. The water flow rates can be adjusted by varying the pump pressures, and the water pressure drop across the reactor was monitored using pressure meters. All experiments were repeated at least twice, and the standard deviations are shown as error bars in the figures. The cell voltages are reported without any iR compensation. H 2 O 2 concentrations were measured using the potassium titanium (IV) oxalate method (Sellers, 1980 ). The FE and energy consumption (EC) of H 2 O 2 production were calculated according to Eqs. 2 – 3 . where n is the electron transfer number for one O 2 molecule reduction to H 2 O 2 (n = 2), F is the Faraday constant (96,485 C/mol), c is the measured H 2 O 2 concentration (mg/L), Q is the flow rate (mL/min), M is the molar mass of H 2 O 2 (34.01 g/mol), I is the applied current (A), EC is the electric energy consumption of H 2 O 2 production (kWh/kg H 2 O 2 ), U is the cell voltage (V). Characterizations The surface morphology and elemental maps of PSE wafers were analyzed by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) using Su8220 SEM (Zeiss Merlin Co.,Ltd., Germany) with a X-Max EDS (Oxford, UK). All samples were sputtered with a layer of gold before analysis. X-ray micro computed tomography (micro-CT) of PSE wafers was performed using a nanoVoxel-4000 system (Sanying Precision Instruments) with a voxel resolution of 10 µm. Samples were scanned over 360° at 0.25° intervals (120 projections), and three-dimensional (3D) reconstructions of the micro-CT results were processed using Avizo software, following the Lambert–Beer law for grayscale segmentation. The ion transfer resistance of PSE wafers and resin microsphere-packed layers was measured by electrochemical impedance spectroscopy (EIS), using the protocol described (Zhao et al., 2025 ). The porosity of PSE wafers was measured by mercury porosimetry using a Micromeritics AutoPore V 9600 system. The porosity of resin microsphere-packed bed is calculated using Eq. 4 . $$\:\epsilon\:=\:\frac{m}{\rho\:V}\times\:100\%$$ 4 where m is the mass of resin microspheres (g), ρ is the density (1.03 g/cm 3 ), and V is the volume of PSE chamber. Declarations Acknowledgements This work was supported by Tsinghua-Toyota Joint Research Fund (20223930086 to Y.W.), National Key Research and Development Program (2022YFC3203005 to Y.W.), and Tsinghua University Initiative Scientific Research Program (2025Z02ORD001). References An, J., Feng, Y., Zhao, Q., Wang, X., Liu, J., Li, N., 2022. Electrosynthesis of H2O2 through a two-electron oxygen reduction reaction by carbon based catalysts: From mechanism, catalyst design to electrode fabrication. Environmental Science and Ecotechnology 11. Cao, P., Quan, X., Zhao, K., Zhao, X., Chen, S., Yu, H., 2021. Durable and Selective Electrochemical H2O2 Synthesis under a Large Current Enabled by the Cathode with Highly Hydrophobic Three-Phase Architecture. Acs Catal 11, 13797-13808. Chen, F.Y., Elgazzar, A., Pecaut, S., Qiu, C., Feng, Y.G., Ashokkumar, S., Yu, Z., Sellers, C., Hao, S.Y., Zhu, P., Wang, H.T., 2024. 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Electro-synthesis of pure aqueous H2O2 on nitrogen-doped carbon in a solid electrolyte flow cell without using anion exchange membrane. Chem Eng J 466. Ruggiero, B.N., Lu, X.K., Adonteng, K., Dong, J., Notestein, J.M., Seitz, L.C., 2024. Local reaction microenvironment impacts on H2O2 electrosynthesis in a dual membrane electrode assembly solid electrolyte electrolyzer. Chem Eng J 486. Sabri Rawah, B., Albloushi, M., Li, W., 2023. Electro-synthesis of pure aqueous H2O2 on nitrogen-doped carbon in a solid electrolyte flow cell without using anion exchange membrane. Chem Eng J 466. Sellers, R.M., 1980. Spectrophotometric determination of hydrogen peroxide using potassium titanium(IV) oxalate. Analyst 105, 950-954. Shin, H., Lee, S., Sung, Y.E., 2023. Industrial-scale H2O2 electrosynthesis in practical electrochemical cell systems. Curr Opin Electroche 38. Wen, Y., Zhang, T., Wang, J., Pan, Z., Wang, T., Yamashita, H., Qian, X., Zhao, Y., 2022. Electrochemical reactors for continuously decentralized H2O2 production. Angew Chem Int Ed Engl. Xia, C., Xia, Y., Zhu, P., Fan, L., Wang, H., 2019. Direct electrosynthesis of pure aqueous H2O2 solutions up to 20% by weight using a solid electrolyte. Science 366, 226-231. Xia, Y., Zhu, P., Yang, Y.L., Qiu, C., Wang, H.T., 2025. Electrochemical Manufacturing of Hydrogen Peroxide with High Concentration and Durability. Acs Catal 15, 4560-4569. Yi, K., Li, C., Hu, S., Yuan, X., Logan, B.E., Yang, W., 2025. High H2O2 production in membrane-free electrolyzer via anodic bubble shielding towards robust rural disinfection. Nature Communications 16. Zhang, X., Xia, Y., Xia, C., Wang, H.T., 2020. Insights into Practical-Scale Electrochemical H2O2 Synthesis. Trends Chem 2, 942-953. Zhang, X., Yang, X., Su, B., Gu, Y., Yang, B., Li, Z., Zhang, Q., Lei, L., Dai, L., Hou, Y., 2025. Membrane electrode assembly for hydrogen peroxide electrosynthesis. Nature Reviews Clean Technology 1, 413-431. Zhao, E., Zhang, Y., Zhan, J., Xia, G., Yu, G., Wang, Y., 2025. Optimization and scaling-up of porous solid electrolyte electrochemical reactors for hydrogen peroxide electrosynthesis. Nature Communications 16, 3212. Zhao, E.R., Xia, G.S., Li, Y., Zhan, J.H., Yu, G., Wang, Y.J., 2023. Technoeconomic Assessment of Electrochemical Hydrogen Peroxide Production with Gas Diffusion Electrodes under Scenarios Relevant to Practical Water Treatment. Acs Es&T Engineering 3, 1800-1812. Additional Declarations There is NO Competing Interest. Supplementary Files SItoNC.pdf Additional informaiton on experimental setup, results and discussion Cite Share Download PDF Status: Posted 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. 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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-7636698","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":518525722,"identity":"98b02862-b757-47fa-8a16-f5ee85fe08fb","order_by":0,"name":"Yujue 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17:39:21","extension":"html","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":103369,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7636698/v1/ab972cf660b73275b9256de8.html"},{"id":92617327,"identity":"2d8bb918-ee9c-447f-969d-d2176eebd4b8","added_by":"auto","created_at":"2025-10-01 17:47:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":5492480,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of (a) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with PSE reactor in the continuous flow mode, (b) resin microsphere-packed reactor, (c) resin wafer reactor, (d) the fabrication of PSE wafer, (e and f) SEM images of resin microsphere-pack bed and PSE wafer, (g-i) the distribution of Cl, S, and C in PSE wafer analyzed by SEM-EDS, (j, k) illustrations of interparticle H\u003csup\u003e+\u003c/sup\u003e transfer in the resin microsphere-packed bed and PSE wafer, (l) the selected micro-CT cubic volume and (m and n) three-dimensional reconstruction results of PSE wafer before and after embedded NaCl particles are dissolved in water (blue color in Figs. 1m and n represents the pores inside PSE wafers).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7636698/v1/8d77506c934bd04d97dda35a.png"},{"id":92617323,"identity":"04d6e745-91ab-4b2a-a6ca-b6ccb9cadad6","added_by":"auto","created_at":"2025-10-01 17:47:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1557253,"visible":true,"origin":"","legend":"\u003cp\u003e(a) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations and FEs of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production, (b) cell voltages and electric energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production, and (c) pressure drops as a function of DI water flow rate during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with the microsphere-backed reactor and PSE wafer reactor (4 cm\u003csup\u003e2\u003c/sup\u003e electrode) in the continuous flow mode. Dowex 50W×8 resin microspheres (150–300 μm) were packed with a packing density of ~1100 mg/mL in the microsphere-packed reactor, PSE wafers (mixing ratio of 7 (g):7 (g):1 (mL) for resin microspheres, NaCl, and binder) were installed in the wafer reactor, current density of 100 mA/cm\u003csup\u003e2\u003c/sup\u003e. (d) Stability of the microsphere-packed reactor (with or without AEM) and PSE wafer reactor (without AEM). Current density of 50 mA/cm\u003csup\u003e2\u003c/sup\u003e, flow rate of 1.58 mL/min. All the voltages are reported without iR-correction.\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7636698/v1/44f8895d0a19fd8df536ba42.png"},{"id":92616424,"identity":"b5b779dc-ccca-4139-9884-cc34412ae4d9","added_by":"auto","created_at":"2025-10-01 17:39:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":967246,"visible":true,"origin":"","legend":"\u003cp\u003e(a) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations and FEs of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production, (b) cell voltages and electric energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production, and (c) pressure drops and pumping energy consumption as a function of DI water flow rate during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with the microsphere-backed reactor and PSE wafer reactor (25 cm\u003csup\u003e2\u003c/sup\u003e electrode) in the continuous flow mode. Operating conditions: current density of 100 mA/cm\u003csup\u003e2\u003c/sup\u003e. All the voltages are reported without iR-correction.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7636698/v1/64195d642eca05bcb08e698d.png"},{"id":92617321,"identity":"745d2439-69db-4dea-b52c-04659e57b9b6","added_by":"auto","created_at":"2025-10-01 17:47:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":917302,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis in the recirculating mode, (b) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration and FE, and (c) cell voltage and electric energy consumption during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with the microsphere-backed reactor and PSE wafer reactor (25 cm\u003csup\u003e2\u003c/sup\u003e electrode) in the recirculating flow mode. Operating conditions: current density of 100 mA/cm\u003csup\u003e2\u003c/sup\u003e, DI water flow rate of 5.2 mL/min, cooling water (~4 ℃) was recirculated through the endplate of the reactor at a flow rate of ~20 mL/min to mitigate the thermal decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e during the operation. All the voltages are reported without iR-correction.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7636698/v1/1b5cc359958026915e57c75d.png"},{"id":93451997,"identity":"89d7b3e5-743a-4dbe-8879-dadb384cf987","added_by":"auto","created_at":"2025-10-14 03:48:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9543526,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7636698/v1/c33c3db2-d758-4ea8-b998-f3003dc031ed.pdf"},{"id":92616423,"identity":"32cb093f-0a52-426a-a4d9-4d183cbbf46a","added_by":"auto","created_at":"2025-10-01 17:39:21","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":770300,"visible":true,"origin":"","legend":"Additional informaiton on experimental setup, results and discussion","description":"","filename":"SItoNC.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7636698/v1/07aeb3a5918a9801c071531a.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Electrosynthesis of hydrogen peroxide with anion exchange membrane-free resin wafer reactors","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe development of porous solid electrolyte (PSE) electrochemical reactors marks a significant advancement in the electrochemical synthesis of hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) (Xia et al., 2019). Unlike conventional reactors that rely on aqueous electrolytes such as potassium hydroxide (KOH) and sodium sulfate (Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e), PSE reactors utilize ion-conducting solids (typically ion-exchange resin microspheres) as the electrolyte medium between the anode and cathode (Kim et al., 2022; Chen et al., 2024). This innovative design enables the direct electrosynthesis of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e in pure water, yielding electrolyte-free H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions that can be directly used in various application (e.g., disinfection and environmental remediation) without the need for downstream purification (Deng et al., 2024; Mazzucato et al., 2024). By eliminating liquid electrolytes and associated downstream separation steps, PSE reactors reduce process complexity and operating costs, thereby enhancing their commercial competitiveness (Wen et al., 2022; Shin et al., 2023; Chen et al., 2025). These benefits have generated worldwide interest in the PSE technology, not only for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, but also for other electrochemical processes, such as carbon dioxide reduction and lithium ion recovery (Li et al., 2024; Elgazzar and Wang, 2025; Fang et al., 2025; Liu et al., 2025).\u003c/p\u003e\n\u003cp\u003eDespite their promise, scaling up PSE reactors for industrial applications faces several engineering challenges (Elgazzar and Wang, 2025; Zhao et al., 2025). As illustrated in Fig. 1a, a typical PSE reactor comprises three chambers: an anode chamber, a gas diffusion electrode (GDE) cathode chamber, and a middle PSE chamber densely packed with ion-exchange resin microspheres (Xia et al., 2019). However, achieving uniform packing of resin microspheres becomes increasingly difficult as reactor size increases (Elgazzar and Wang, 2025; Zhao et al., 2025), and even minor nonuniformities in the packing can cause local resistance variations, thus leading to uneven flow field distribution, increased cell voltages, and reduced Faradaic efficiencies (FEs) (Xia et al., 2019; Lin et al., 2025; Zhao et al., 2025).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMoreover, efficient ion transport requires small-diameter resin microspheres packed tightly to maximize interparticle contact (Elgazzar and Wang, 2025; Zhao et al., 2025). However, such dense packing of microspheres results in low porosity (\u0026epsilon;) and thus high pressure drops across the microsphere-packed bed. Consequently, high pumping pressures are required to pass water through the PSE reactor to extract synthesized H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Zhao et al., 2025). The high pressures not only increase energy consumption, but more critically, pose challenges to the stability of the reactor (Elgazzar and Wang, 2025; Zhao et al., 2025). For example, due to the high water pressures, an anion exchange membrane (AEM) has to be placed between the PSE layer and the GDE cathode to prevent the cathode from being quickly flooded by water, while allowing HO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e produced at the cathode to diffuse to the PSE layer (Xia et al., 2019; Zhang et al., 2020; Sabri Rawah et al., 2023; Yi et al., 2025). Unfortunately, the limited mechanical, chemical, and thermal durability of AEMs leads to their gradual degradation during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, posing a critical barrier to long-term stability of PSE reactors (Zhang et al., 2020; Qi et al., 2023; Shin et al., 2023; Zhao et al., 2025).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo address these challenges, we engineered structured PSE wafers composed of ion-exchange resins, conductive binders, and pore-forming agents, then used them as the integrated PSE layer within the reactor. Compared with uniformly packing resin microspheres between the anode and cathode, these wafers can be easily pre-molded with precise geometry, and then conveniently installed into reactors, thereby simplifying reactor assembly and scalability. More importantly, through systematic optimization of composition and molding parameters, thin, robust PSE wafers with both high ionic conductivity and porosity can be fabricated, thus overcoming the inherent trade-off between ion conductivity and hydraulic resistance observed for microsphere-packed beds. Consequently, the PSE wafer reactor can be operated at significantly lower pressure drops without compromising cell voltages and FEs during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis as compared to microsphere-packed reactors. Notably, the reduced water pressures eliminate the need for an AEM to prevent cathode flood during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, circumventing the barrier to long-term stability of PSE reactors. Overall, by addressing key bottlenecks in reactor assembly, scalability, and stability, PSE wafer reactors provide a robust and scalable platform for practical H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, paving the way for the industrial deployment of PSE-based technologies.\u0026nbsp;\u003c/p\u003e"},{"header":"Results ","content":"\u003cp\u003e\u003cstrong\u003eCharacterizations of PSE wafers\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCurrently, resin microspheres made from sulfonic acid (SA) functionalized styrene-divinylbenzene copolymer are commonly used as the ion conductor in PSE reactors for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis (Xia et al., 2019; Perry et al., 2021). Based on previous works (Rawah et al., 2023; Fang et al., 2025; Zhao et al., 2025), Dowex 50 W\u0026times;8 resin microspheres were selected as the PSE conductor in this study because it has a high surface density of SA groups that are favorable for H\u003csup\u003e+\u003c/sup\u003e conduction during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn the PSE reactor, numerous resin microspheres are densely packed into a thin layer to conduct protons (H\u003csup\u003e+\u003c/sup\u003e) from the anode to the cathode along their interconnected surface, while allowing water to flow through their interstitial space to extract produced H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e out of the reactor (see Fig. 1a) (Xia et al., 2019). As illustrated in Fig. 2g, H\u003csup\u003e+\u003c/sup\u003e conduction on the microsphere surface proceeds through a hopping diffusion process between neighboring SA groups (i.e., the Grotthuss mechanism) (Liu et al., 2016; Klumpen et al., 2017), and the rate of H\u003csup\u003e+\u003c/sup\u003e conduction across the PSE layer is mainly limited by interparticle H\u003csup\u003e+\u003c/sup\u003e hopping at the contact points of packed microspheres (Zhao et al., 2025). To enhance the interparticle H\u003csup\u003e+\u003c/sup\u003e conduction, smaller microspheres and higher packing density are desired to increase the contact points among packed microspheres (Zhao et al., 2025). However, while using smaller microspheres or higher packing densities can enhance the interparticle H\u003csup\u003e+\u003c/sup\u003e conduction and thus reduce the resistance of H\u003csup\u003e+\u003c/sup\u003e conduction (R\u003csub\u003es\u003c/sub\u003e) of the PSE layer, the porosity (\u0026epsilon;) of the layer decreases (see Table 1). This will considerably increase the pressure drop across the layer according to the Kozeny-Carman equation (Eq. 1).\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" style=\"width: 334px; height: 52.079px;\" width=\"334\" height=\"52.079\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u0026Delta;P is the pressure drop across the PSE bed, \u0026mu; is the viscosity of water, \u0026epsilon; is the porosity of the bed, L is total height of the bed, \u0026Phi;\u003csub\u003es\u003c/sub\u003e is the sphericity of microspheres in the packed bed (\u0026Phi;\u003csub\u003es\u003c/sub\u003e = 1 for spherical particles), d\u003csub\u003ep\u003c/sub\u003e is the diameter of the volume equivalent spherical particle, u is the superficial velocity, Q is the volumetric flow rate of the fluid, and A is the cross-sectional area of the bed perpendicular to the water flow direction.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOn the other hand, while using larger microspheres or lower packing densities increases the porosity of the layer, the R\u003csub\u003es\u003c/sub\u003e of the layer increased (Table 1), which will substantially increase the cell voltage and energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis (Zhao et al., 2025). Therefore, there exists an inherent trade-off between the ion conductivity and porosity of microsphere-packed beds when they are used as the PSE layer in PSE reactors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u0026nbsp;\u003c/strong\u003eProton conduction resistance and porosity of resin microsphere-packed beds and resin wafers.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 20px;\"\u003e\n \u003cp\u003ePSE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003eParameters\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 9px;\"\u003e\n \u003cp\u003eR\u003csub\u003es\u003c/sub\u003e (\u0026Omega;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 10px;\"\u003e\n \u003cp\u003ePorosity (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 32px;\"\u003e\n \u003cp\u003eDiameter (\u0026mu;m)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003ePacking density (mg/mL)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"6\" valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003eResin microsphere-packed bed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 32px;\"\u003e\n \u003cp\u003e150\u0026ndash;300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e3.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 32px;\"\u003e\n \u003cp\u003e150\u0026ndash;300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003e1000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e2.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 32px;\"\u003e\n \u003cp\u003e150\u0026ndash;300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003e1100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e1.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 32px;\"\u003e\n \u003cp\u003e35\u0026ndash;75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003e1200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e1.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 32px;\"\u003e\n \u003cp\u003e75\u0026ndash;150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003e1200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e1.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 32px;\"\u003e\n \u003cp\u003e300\u0026ndash;1000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003e950\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e2.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003eMixing ratio of resin microspheres (g), NaCl (g), and bind (mL)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003eResin wafer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e5:9:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e1.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e7:7:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e39\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e9:5:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9px;\"\u003e\n \u003cp\u003e1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eNotably, by tuning the mixing ratios of resin microspheres, pore forming agent (sodium chloride particles), and conductive binder (sulfonated polyetheretherketone), the PSE wafers achieved both high ion conductivity and porosity simultaneously (Table 1). As shown in the SEM image (Fig. 1f), the binder filled the interstices of resin microspheres and bound them together. Because the binder can also transport H\u003csup\u003e+\u003c/sup\u003e through the hopping diffusion process between neighboring surface SA groups, it significantly increases ion-conducting pathways at the contact points of microspheres (Fig. 1k). Therefore, the interparticle H\u003csup\u003e+\u003c/sup\u003e conduction among resin microspheres is substantially enhanced in the PSE wafer, overcoming the bottleneck of H\u003csup\u003e+\u003c/sup\u003e conduction across the microsphere-packed bed. Meanwhile, high porosity (e.g., 36%\u0026ndash;50%) could be obtained after the pore forming agent (NaCl) embedded in the wafer was dissolved in water (see Fig. 1n). The PSE wafer thus overcomes the trade-off between ion conductivity and porosity as observed for microsphere-packed beds.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn addition, PSE wafers can be pre-molded with a precise geometry and uniform thickness, then easily assembled into reactor, which can considerably promote the uniform contact between PSE, membrane, and electrodes (see Fig. 1c and Fig. S1). In comparison, uniformly packing resin microspheres between the anode and cathode is laborious and challenging, especially in large reactors (Zhao et al., 2025), and variations in the packing can result in non-uniform PSE/membrane/electrode contact and thus resistance fluctuations among different experimental runs or PSE reactors (Elgazzar and Wang, 2025). Therefore, we anticipate that compared with resin microsphere-packed beds, PSE wafers can effectively improve the scalability and reproducibility of PSE reactors (see below).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with microsphere-packed and wafer reactors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe performance of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis using the microsphere-packed reactor and PSE wafer reactor are compared in Fig. 2 and Fig. S8. For the microsphere-packed reactor, previous studies have shown that PSE layers packed with 150\u0026ndash;300 \u0026mu;m resin microspheres and a packing density of ~1100 mg/mL best balance the trade-off between ion conductivity and porosity for efficient and stable H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis (Zhao et al., 2025). The same setting was therefore adopted to assemble the microsphere-packed reactor used in this study. For the wafer reactor, PSE wafers fabricated with a mixing ratio 7 (g):7 (g):1 (mL) of resin microspheres, NaCl particles, and binder were used. As reported in Table 1, the resin wafers achieved a similar H\u003csup\u003e+\u003c/sup\u003e conductivity (R\u003csub\u003es\u003c/sub\u003e = 1.83 \u0026Omega;) at a significantly higher porosity (\u0026epsilon; = 39%) than the microsphere-packed layer (R\u003csub\u003es\u003c/sub\u003e = 1.77 \u0026Omega;, \u0026epsilon; = 11%) (Fig. S4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig. 2a and Fig. S8a show that under the same operating conditions (identical current densities and flow rates), the wafer reactor produced similar or slightly higher concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e than the microsphere-packed reactor. Meanwhile, the cell voltage of the wafer reactor was only marginally higher than that of the microsphere-packed reactor (Fig. 2b), possibly due to the slightly higher R\u003csub\u003es\u003c/sub\u003e of the wafer. Therefore, the electric energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production are generally comparable for the two reactors (Fig. 2b). In contrast, the pressure drops across the two reactors were significantly different (Fig. 2c). Due to its lower porosity, the pressure drops across the microsphere-packed reactor increased rapidly with increasing flow rates (k = 9.488), reaching ~100 kPa at a flow rate of 10 mL/min. In comparison, the pressure drops across the wafer reactor increased only slowly (k = 2.105) with increasing flow rates. Consequently, the pressure drop across the wafer reactor was only ~20 kPa at the highest flow rate tested in this study. Compared to the microsphere-packed reactor, the wafer reactor can thus dramatically reduce the pumping energy consumption during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, especially when high flow rates are applied (see Fig. S10).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe results shown above highlight that by addressing the inherent trade-off between ion conductivity and porosity of microsphere-packed reactors, resin wafers can significantly reduce the pressure drop across PSE reactors, while maintaining high FEs and low cell voltages during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis. In contrast, while decreasing the packing density or increasing the particle size of resin microspheres could also increase the porosity of microsphere-packed beds and thus reduce the pressure drop across the reactor, the H\u003csup\u003e+\u003c/sup\u003e conductivity of the bed decreased considerably, thereby resulting in substantially higher cell voltages and electric energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production (see Fig. S5 for more detail).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDue to the high pressure drop across the microsphere-packed reactor, an AEM had to be placed between the PSE bed and the GDE cathode to prevent electrode flooding during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis (Xia et al., 2019; Zhao et al., 2025). Otherwise, the performance of the microsphere-packed reactor deteriorated quickly in only a few hours due to the electrode flooding (see Fig. 2d). While the use of AEM improved the operational stability of microsphere-packed reactors, the AEM would retain some of the produced H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at the cathode/AEM interface, resulting in over-reduction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to H\u003csub\u003e2\u003c/sub\u003eO (Shin et al., 2023; Xia et al., 2025). This effect is more significant when low water flow rates are applied to produce high-concentration H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions (Xia et al., 2025), thereby causing the lower H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations and FEs of the microsphere-packed reactor than the wafer reactor at flow rates lower than 5.21 mL/min (see Fig. 2a). Moreover, the AEM introduces additional ohmic resistance and will thus increase cell voltages in the microsphere-packed reactor (Shin et al., 2023). More critically, AEMs are susceptible to gradual degradation due to mechanical stress, thermal effects, and chemical reactions during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis (Rawah et al., 2023; Xia et al., 2025; Zhao et al., 2025). Consequently, the performance of microsphere-packed reactor declined progressively after ~76 h (Fig. 2d), primarily due to the increasing electrode flooding as the AEM was gradually degraded (see Fig. S7 for more information).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn contrast to the microsphere-packed reactor, the reduced water pressures allow the wafer reactor to be stably operated without using an AEM to separate the GDE and PSE layer. As shown in Fig. 2d, the wafer reactor operated stably during the long-term evaluation, and no electrode flood was observed at the end of the test. The wafer reactor can thus avoid the efficiency and long-term stability problems associated with the use of AEM for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eScalability evaluation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo evaluate the scalability of microsphere-packed and wafer reactors, we increased the electrode area from 4 cm\u003csup\u003e2\u003c/sup\u003e (2 cm \u0026times; 2 cm) to 25 cm\u003csup\u003e2\u003c/sup\u003e (5 cm \u0026times; 5 cm), and then tested the enlarged reactors for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis. Compared with their smaller counterparts, the two enlarged reactors increased the concentration of synthesized H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions by 5.9\u0026ndash;6.4 times under the same operating conditions (Figs. 3a). These increases are almost the same as the increase of electrode area (6.25 times), indicating that there are no significant changes in FEs of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production during the reactor scaling up (Fig. 3a and Fig. S9a). Meanwhile, the cell voltages increased only moderately for the enlarged reactors than the smaller reactors (Fig. 3b and Fig. S9b), possibly due to the uneven current distribution and mass transfer as the electrode size increases (Martinez-Huitle et al., 2015; An et al., 2022; Cui et al., 2024). Therefore, the electric energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production increased only modestly for the enlarged reactors compared to their smaller counterparts (Fig. 3b).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNote that during the reactor enlargement, both the height (L) and the cross-sectional area perpendicular to the water flow (A) of the microsphere-packed bed or wafer increased by the same factor (2.5 times), which will effectively balance their influences on pressure drop according to the Kozeny-Carman equation (Eq. 1). Therefore, it is expected that for the same flow rate, the pressure drops through the smaller and enlarged reactors will not change considerably. Consistent with the theoretical prediction, the pressure drops across the enlarged wafer reactor remained almost the same as its smaller counterpart during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis (Figs. 2c and 3c). However, the pressure drops across the enlarged microsphere-packed reactor increased by ~10\u0026ndash;15 kPa than its smaller counterpart during most experiments. These increases are possibly caused by slight variations in the packing of resin microspheres, which is difficult to control in large reactors (Elgazzar and Wang, 2025; Zhao et al., 2025). In comparison, the properties of PSE wafers (e.g., geometry, ion conductivity, and porosity) can be more precisely and uniformly controlled during fabrication. Therefore, the performance of wafer reactors is more reproducible, which is important for reactor scaling up and practical applications.\u003c/p\u003e\n\u003cp\u003eWith current densities of 100\u0026ndash;150 mA/cm\u003csup\u003e2\u003c/sup\u003e, the enlarged wafer reactor produced up to ~16200\u0026ndash;21000 mg/L (1.62\u0026ndash;2.10 wt%) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at a flow rate of 1.58 mL/min in the continuous flow mode (see Fig. 3a and SI Fig. S9a). To further increase the concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions, the product stream can be recirculated through the reactor (or passing consecutively through reactor stacks) until desired H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations are reached (see Fig. 4a for the operation scheme) (Ruggiero et al., 2024; Xia et al., 2025). Fig. 4b shows that as the product stream was recirculated through the wafer reactor, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations increased to ~11 wt% after 90 min operation, while maintaining a high FE of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production of ~92%. In comparison, FEs decreased gradually during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with the microsphere-packed reactor, possibly due to the enhanced H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e decomposition at the cathode/AEM interface as H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations increase (Deng et al., 2024; Xia et al., 2025; Zhang et al., 2025). As a result, a lower H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration (9.25 wt%) and FE (77%) was obtained at the end of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with the microsphere-packed reactor. Note that during the recirculation operation, a relatively high water flow rate of 5.2 mL/min was applied to enhance the transport of the generated H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e away from the cathode surface, and thus to minimize its further reduction (Ruggiero et al., 2024; Xia et al., 2025). Nevertheless, it seems that this approach is less effective for the microsphere-packed reactor because of the separation of the cathode and water stream by the AEM.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig. 4c show that during the recirculation operation, cell voltages increased gradually for the microsphere-packed reactor, but were generally stable for the wafer reactor. The increases of cell voltages can be mainly attributed to the generation and accumulation of gas bubbles in the reactors during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis (Zhao et al., 2023; Elgazzar and Wang, 2025). As H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations increase during the recirculation operation, self- and thermal decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is enhanced in the reactor, which can generate some oxygen gas bubbles in the PSE layer. Due to the lower porosity of microsphere-packed beds, the bubbles are less effectively removed from the microsphere-packed reactor by the passing water stream than from the wafer reactor. Consequently, more gas bubbles accumulated in the microsphere-packed reactor, which would disrupt ion conduction and thus result in higher cell voltages (Kim et al., 2020; Lazaridis et al., 2022; Elgazzar and Wang, 2025).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on the FEs and cell voltages observed during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, the electrical energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production are calculated using Eq. 3. Due to the decreases of FEs and increases of cell voltages, the energy consumption increased during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with the microsphere-packed reactor (Fig. 4c). When a 9.25 wt% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solution was obtained, the energy consumption is 9.23 kWh/kg H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (on a 100 wt% basis). This value is about the same as that reported for microsphere-packed reactors tested under similar experimental conditions in a recent study (~11.3 kWh/kg H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e for 10 wt% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions, see SI Table S1 for more detail) (Xia et al., 2025). In comparison, energy consumption remained relatively stable at ~6 kWh/kg H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis with the wafer reactor because of the insignificant changes of FEs and cell voltages. In addition, compared with conventional reactors using aqueous electrolytes, the resin wafer reactor demonstrated generally higher FEs when producing H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions of the same concentrations (see Table S1). These findings underscore the potential of the wafer reactor as a more energy-efficient alternative to conventional reactors, in addition to the benefit of avoiding the cost associated with aqueous electrolytes and downstream separation, which can substantially increase operational expenses (Cao et al., 2021; Zhao et al., 2023).\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, we have developed robust PSE wafers with both high ionic conductivity and porosity to address key engineering challenges faced by current PSE reactors that use resin microsphere-packed beds as the PSE layer for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis. Because of their higher porosity, the PSE wafers dramatically reduced the pressure drops across the reactor during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis compared to resin microsphere-packed reactors. This improvement enables stable operation of the wafer reactors without the need for an AEM to mitigate GDE flooding during H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, thereby circumventing a critical barrier to long-term stability of PSE reactors associated with AEM use. Additionally, the high conductivity of PSE wafers facilitates efficient H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production with high FEs and low energy consumption. Furthermore, the molding process employed for wafer fabrication ensures precise geometry and high uniformity, which substantially improve the assembly, scalability, and reproducibility of PSE reactors. Overall, by addressing the key limitations of resin microsphere-packed beds, the PSE wafer significantly enhance the feasibility of PSE reactors for practical H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis, as well as other electrochemical processes such as CO\u003csub\u003e2\u003c/sub\u003e reduction.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003eMaterials and chemicals\u003c/h2\u003e\u003cp\u003eResin microspheres (150\u0026ndash;300 \u0026micro;m), NaCl (99%), N,N-Dimethylformamide (DMF, 99.5%) anhydrous ethanol (99.8%) were purchased from Sigma-Aldrich. Sulfonated polyetheretherketone (SPEEK, 60% sulfonated) was purchased from Zhongheng New Materials Technology Co., LTD. Hydrophobic GDL carbon paper (HCP135, Hesen Co., Ltd., China), IrO\u003csub\u003e2\u003c/sub\u003e (Accelerate\u0026reg;), black carbon (BP2000), Nafion-115 membrane (PEM), nafion solution (D520, 5wt.%) and sustainion X37-50 Grade RT membrane (AEM) were purchased from SCI Materials Hub. Alkymer anion exchange resin binder solution (I-250, 5wt.%) was purchased from EVE Hydrogen Energy Co., LTD. All experiments used Millipore water (18.2 MΩ cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eFabrication of PSE wafers\u003c/h3\u003e\n\u003cp\u003eTo fabricate resin wafers, appropriate amounts of resin microspheres, NaCl crystals, and binder (SPEEK dissolved in DMF with 15% mass fraction) were uniformly mixed in a mortar. The mixture was then transferred into the cavity of stainless steel molds and pressed with a pressure of 10 kPa at room temperature for 12 h. After the molding process, the obtained PSE wafers were washed with deionized water to dissolve NaCl particles embedded in the matrix, then dried at 70 ℃ for 24 h prior to installation into PSE reactors. The ion conductivity and porosity of the wafers can be adjusted by varying the mixing ratios of resin microspheres, NaCl, and binder.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003ePreparation of GDE cathode and IrO\u003csub\u003e2\u003c/sub\u003e anode\u003c/h2\u003e\u003cp\u003eNine milligrams of carbon black (BP2000), 90 \u0026micro;L of alkymer anion exchange resin binder solution (I-250, 5 wt%), and 10 mL of 75% ethanol were mixed in an ultrasonic bath for 30 min. The obtained homogeneous ink was then sprayed onto a 3 cm \u0026times; 3 cm carbon paper (HCP 135) at 40\u0026deg;C. Next, the carbon paper was naturally dried at room temperature for 24 h to prepare GDE cathodes for PSE reactors. To prepare the anode, IrO\u003csub\u003e2\u003c/sub\u003e (4.5 mg) and Nafion solution (40 \u0026micro;L, D520, 5wt.%) were dispersed into 5 ml of ethanol under ultrasonication. After 30 min ultrasonication, the as-prepared ink was then sprayed onto a 3 cm \u0026times; 3 cm Nafion-115 membrane at 70\u0026deg;C to prepare the catalyst-coated membrane (CCM) anode used in PSE reactors.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003ePSE reactor configurations and HO electrosynthesis\u003c/h3\u003e\n\u003cp\u003eThe configurations of resin microsphere-packed reactor and wafer reactor are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and c. Both reactors had an IrO\u003csub\u003e2\u003c/sub\u003e anode and GDE cathode for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), respectively. In the microsphere-packed reactor, the anode and cathode sandwiched a PEM (Nafion-115), a layer of densely packed resin microspheres (thickness of 2 mm), and an AEM (sustainion X37-50). In comparison, the anode and cathode in the wafer reactor sandwiched a PEM and a pre-molded resin wafer, without using an AEM to separate the wafer and the cathode.\u003c/p\u003e\u003cp\u003eDuring H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis experiments, an oxygen gas (50 mL/min) was fed through the cathode chamber to provide oxygen for ORR, while a DI water stream was passed through the middle PSE chamber using a peristaltic pump. The water flow rates can be adjusted by varying the pump pressures, and the water pressure drop across the reactor was monitored using pressure meters. All experiments were repeated at least twice, and the standard deviations are shown as error bars in the figures. The cell voltages are reported without any iR compensation.\u003c/p\u003e\u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations were measured using the potassium titanium (IV) oxalate method (Sellers, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1980\u003c/span\u003e). The FE and energy consumption (EC) of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production were calculated according to Eqs.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cimg 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\" style=\"width: 394px; height: 88.8491px;\" width=\"394\" height=\"88.8491\"\u003e\u003c/p\u003e\u003cp\u003ewhere n is the electron transfer number for one O\u003csub\u003e2\u003c/sub\u003e molecule reduction to H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (n\u0026thinsp;=\u0026thinsp;2), F is the Faraday constant (96,485 C/mol), \u003cem\u003ec\u003c/em\u003e is the measured H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration (mg/L), \u003cem\u003eQ\u003c/em\u003e is the flow rate (mL/min), M is the molar mass of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (34.01 g/mol), \u003cem\u003eI\u003c/em\u003e is the applied current (A), EC is the electric energy consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e production (kWh/kg H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e), \u003cem\u003eU\u003c/em\u003e is the cell voltage (V).\u003c/p\u003e\n\u003ch3\u003eCharacterizations\u003c/h3\u003e\n\u003cp\u003eThe surface morphology and elemental maps of PSE wafers were analyzed by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) using Su8220 SEM (Zeiss Merlin Co.,Ltd., Germany) with a X-Max EDS (Oxford, UK). All samples were sputtered with a layer of gold before analysis. X-ray micro computed tomography (micro-CT) of PSE wafers was performed using a nanoVoxel-4000 system (Sanying Precision Instruments) with a voxel resolution of 10 \u0026micro;m. Samples were scanned over 360\u0026deg; at 0.25\u0026deg; intervals (120 projections), and three-dimensional (3D) reconstructions of the micro-CT results were processed using Avizo software, following the Lambert\u0026ndash;Beer law for grayscale segmentation. The ion transfer resistance of PSE wafers and resin microsphere-packed layers was measured by electrochemical impedance spectroscopy (EIS), using the protocol described (Zhao et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The porosity of PSE wafers was measured by mercury porosimetry using a Micromeritics AutoPore V 9600 system. The porosity of resin microsphere-packed bed is calculated using Eq.\u0026nbsp;\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:\\epsilon\\:=\\:\\frac{m}{\\rho\\:V}\\times\\:100\\%$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ewhere m is the mass of resin microspheres (g), ρ is the density (1.03 g/cm\u003csup\u003e3\u003c/sup\u003e), and V is the volume of PSE chamber.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThis work was supported by Tsinghua-Toyota Joint Research Fund (20223930086 to Y.W.), National Key Research and Development Program (2022YFC3203005 to Y.W.), and Tsinghua University Initiative Scientific Research Program (2025Z02ORD001).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAn, J., Feng, Y., Zhao, Q., Wang, X., Liu, J., Li, N., 2022. 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Acs Es\u0026amp;T Engineering 3, 1800-1812.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7636698/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7636698/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePorous solid electrolyte (PSE) reactors have attracted worldwide interest in H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis and other electrochemical processes (e.g., CO\u003csub\u003e2\u003c/sub\u003e reduction). However, scaling up PSE reactors for industrial applications faces several challenges, including the difficulty in uniformly packing PSE (typically resin microspheres) in large reactors, the high pressure drop across the reactor, and the limited durability of anion exchange membranes (AEM). Here, to address these challenges, we fabricated robust PSE wafers with both high ion conductivity and porosity by pre-molding resin microspheres, conductive binder, and pore-forming agent. These pre-molded wafers can be easily installed in reactors, thereby simplifying the reactor assembly and scalability. Moreover, due to their high porosity, the PSE wafers dramatically reduced the pressure drops across the reactor by a factor of ~ 5–7 compared to resin microsphere-packed beds. Consequently, the wafer reactors could be stably operated without the need of an AEM for preventing electrode flooding, circumventing the barrier to long-term stability of PSE reactors. By addressing these bottlenecks, the wafer reactor provide a robust and scalable platform for practical H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e electrosynthesis.\u003c/p\u003e","manuscriptTitle":"Electrosynthesis of hydrogen peroxide with anion exchange membrane-free resin wafer reactors","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-01 17:39:16","doi":"10.21203/rs.3.rs-7636698/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e3075a7b-d2e6-47ca-942f-6d0e4aca955e","owner":[],"postedDate":"October 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":55094012,"name":"Physical sciences/Engineering/Chemical engineering"},{"id":55094013,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Electrocatalysis"}],"tags":[],"updatedAt":"2025-10-14T03:40:12+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-01 17:39:16","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7636698","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7636698","identity":"rs-7636698","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}