Interfacial Microenvironment Engineering in Pickering Emulsion Electrocatalytic System for Selective Hydrogenation of 4-Nitrostyrene

Interfacial Microenvironment Engineering in Pickering Emulsion Electrocatalytic System for Selective Hydrogenation of 4-Nitrostyrene | 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 Interfacial Microenvironment Engineering in Pickering Emulsion Electrocatalytic System for Selective Hydrogenation of 4-Nitrostyrene Chenhui Han, Yifan Wang, Lijun Li, Yuliang Gao, Xuzhuang Yang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8332714/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Tuning reaction selectivity by modifying the microenvironment around active sites is an intriguing research focus in catalysis. Here, we show that the selectivity of 4-nitrostyrene hydrogenation can be modulated via interfacial microenvironment engineering in a Pickering emulsion electrocatalytic system, where an interfacial effect derived from the unique structure of the electric double layer and interfacial hydrogen-bonding interactions steers the hydrogen transfer pathway. Specifically, hydrophilic Pt/CNTs-AT preserves the intact interfacial hydrogen-bond network, facilitating efficient proton-coupled electron transfer that preferentially reduces the nitro group, thus achieving 95.2% selectivity for 4-aminostyrene. In contrast, hydrophobic Pt/CNTs-C18 disrupts the hydrogen-bond network and alters the electric double layer structure, promoting the formation of adsorbed hydrogen and thus directing the reaction toward C = C bond hydrogenation, with 93.3% selectivity for 4-nitroethylbenzene. This work provides new insights into the selective hydrogenation of multifunctional substrates, highlighting the critical role of interfacial microenvironment regulation in steering reaction pathways. Physical sciences/Chemistry/Electrochemistry/Electrocatalysis Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis Physical sciences/Chemistry/Catalysis/Catalytic mechanisms Physical sciences/Materials science/Soft materials/Colloids Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Electrocatalytic hydrogenation (ECH) is a promising strategy for the hydrogenation of unsaturated substrates, where water serves as a sustainable hydrogen source 1 – 3 . This technique has attracted considerable attention owing to its inherent advantages, including mild reaction conditions, low energy consumption, and high operational safety 4 , 5 . However, a critical challenge limiting its efficiency lies in the poor solubility of most substrates in aqueous electrolytes, which severely restricts the accessibility of reactants to catalytic active sites. A rationally designed approach to address this limitation is to conduct ECH reactions directly at the oil-water interface, leveraging the unique microenvironment of this phase boundary to enhance reaction kinetics. The oil-water interface possesses distinct physicochemical properties, such as preferential molecular orientation 6 – 8 , distinctive electron/ion transfer kinetics 9 – 11 , and ultrahigh reaction efficiency derived from microinterfacial effects 12 , 13 . These features offer significant opportunities to optimize catalytic performance by precisely regulating the microenvironment surrounding catalytic active sites. Among various interfacial systems, Pickering emulsions stabilized by amphiphilic solid particles exhibit exceptional long-term stability, making them an ideal platform for the assembly of catalysts at the oil-water interface 14 , 15 . In our previous work 16 , we achieved efficient ECH of alkenes in an oil-in-water (O/W) Pickering emulsion electrocatalytic system (PEES), delivering a current density of 149 mA·mgPd⁻¹ and a faradaic efficiency of 96%, significantly outperforming its conventional single-phase counterpart. However, the influence of the oil-water interfacial microenvironment on reaction selectivity remains elusive. In this study, we reveal a novel interfacial effect that is closely correlated with the oil-water distribution near catalytic sites. This effect significantly modulates the selectivity of the ECH of 4-nitrostyrene (4-NS) in PEES. Pt nanoparticles supported on hydrophilic carbon nanotubes (CNTs) exhibited high activity toward nitro group hydrogenation, achieving 95.2% selectivity for 4-aminostyrene (4-AS). In contrast, Pt nanoparticles supported on hydrophobic CNTs favored the hydrogenation of C = C bonds, with 93.3% selectivity for 4-nitroethylbenzene (4-NE). Through a combination of experimental investigations and computational simulations, we uncovered a previously unreported interfacial effect arising from the unique structure of the electric double layer and hydrogen-bonding interactions at the oil-water interface. This effect modulates hydrogen transfer pathways, selectively directing the reaction along either the Eley-Rideal or Langmuir-Hinshelwood mechanism 17 – 19 to preferentially reduce nitro groups or C = C bonds, respectively. Results Preparation and characterization of catalysts and Pickering emulsions CNTs are ideal support materials for constructing PEES, owing to their high electrical conductivity and facile molecular functionalization. The synthesis protocols, nomenclature, and hydrophilic/hydrophobic properties of the four CNT supports investigated herein are illustrated in Fig. 1 a. The as-received commercial CNTs exhibit a hydrophobic surface. Following acid treatment, their surface becomes hydrophilic due to the introduction of oxygen-containing functional groups (designated as CNTs-AT). Subsequent amidation reactions were performed to graft alkyl chains of varying lengths onto the surface of CNTs-AT, yielding CNTs-C8 and CNTs-C18 with distinct hydrophobicity. The resulting samples exhibited contact angles of 123.4° and 155.9°, respectively. Pre-synthesized monodisperse Pt nanoparticles (Fig. 1 c) were then uniformly deposited onto the four supports to fabricate the corresponding catalysts (Fig. 1 d, Figure S1 -2). X-ray photoelectron spectroscopy (XPS) analysis of the C 1s region revealed the disappearance of the O-C = O peak at 289.1 eV following amidation grafting (by comparing Pt/CNTs-AT and Pt/CNTs-C18), indicating that the carboxyl groups on CNTs-AT were involved in the amidation reaction (Fig. 1 b). Concomitantly, in the O 1s spectrum, the area of the C-O peak (at 533.4 eV) was significantly reduced, while a distinct N-H peak emerged in Pt/CNTs-C18 after grafting (Figure S3). These observations suggest that the carboxyl groups lose their -OH moieties to form C-N bonds during this process. Collectively, these results confirm the successful modification of CNTs with hydrophobic alkyl chains. For both Pt/CNTs-AT and Pt/CNTs-C18, the Pt 4f 5/2 and Pt 4f 7/2 peaks were detected at 75.1 eV and 71.7 eV 20 , respectively, indicating that Pt primarily exists in the metallic state and that its chemical state remains unaffected by the support. Among the four CNT candidates, CNTs-AT exhibited the optimal performance in stabilizing Pickering emulsions. Given that highly hydrophobic CNTs alone are incapable of stabilizing emulsions, CNTs-AT (without Pt nanoparticles) was added at a 1:1 ratio to the PEES of all four catalysts to assist emulsification (Figure S4). For example, the emulsion prepared with 5 mg of Pt/CNTs-C18 catalyst and 5 mg of CNTs-AT is designated as Pt/CNTs-C18 PEES. All four emulsions showed average droplet sizes in the range of 100–200 µm (Figure S5). Scanning electron microscopy (SEM) images of freeze-dried PEES revealed an ultrathin (≈ 40 nm, corresponding to 1–2 layers of carbon nanotubes) three-dimensional interconnected network structure on the droplet surface stabilized by Pt/CNTs-AT (Fig. 1 e–f). In contrast, the Pt/CNTs-C18 emulsion formed a denser, slightly thicker network with clear interconnections between droplets (Fig. 1 g, Figure S6). This interconnected state ensures electron transfer across droplets at the oil-water interface. The aggregation of CNTs on droplet surfaces was further verified by droplet solidification technology 21 , 22 and confocal laser scanning microscopy (CLSM) (Figure S7-9). This interfacial assembly behavior ensures the localization of Pt nanoparticles near the oil-water interface of the droplets. Selectivity regulatory behavior on the PEES interface Electrochemical tests were performed in a customized reactor (Fig. 2 a) adopting a three-electrode configuration analogous to an H-type cell, where the cathode and anode compartments were separated by a Nafion 117 membrane. The cathode compartment was filled with Pickering emulsion, and an annular Ag foil (5 cm²) was inserted into the emulsion phase to serve as the current collector. A homogenizer mounted at the top of the cathode compartment could operate intermittently to eliminate concentration gradients and enhance mass transfer. The potential of zero charge (PZC) of the Ag current collector reflects its surface charge property in the electrolyte, corresponding to the potential at which the differential capacitance reaches a minimum. As illustrated in Fig. 2 b, the PZC of the Ag current collector was determined to be -0.45 V RHE , indicating that its surface maintains a positive charge until the applied potential shifts to a value more negative than − 0.45 V RHE . In the Pt/CNTs-AT and Pt/CNTs-C18 PEES, the emulsion droplets stabilized by negatively charged CNTs-AT (Figure S10) were adsorbed onto the current collector and neutralized its surface charge, thereby shifting the PZC of the current collector to a value near zero. This phenomenon implies the formation of an electrical connection between the CNTs and the current collector, which facilitates electron transfer to the CNTs at the oil-water interface for catalyzing the reactions therein. Linear sweep voltammetry (LSV) curves of two representative PEES in 0.5 M H₂SO₄ electrolyte demonstrate that both the hydrophilic (Pt/CNTs-AT PEES) and hydrophobic (Pt/CNTs-C18 PEES) systems exhibit nearly identical onset potentials for the hydrogen evolution reaction (HER) (dashed lines, Fig. 2 c). In contrast, in the presence of 4-NS, the Pt/CNTs-AT PEES shows a considerably lower onset potential than the Pt/CNTs-C18 PEES (solid lines). This result indicates that the interfacial environment, not merely the catalyst alone, exerts a significant influence on the hydrogenation process of 4-NS. Furthermore, the onset potentials in the presence of 4-NS are lower than those in its absence, suggesting that the electrocatalytic reduction of 4-NS is thermodynamically more favorable than that of HER. ECH of 4-NS was first investigated in a single-phase system at -0.4 V RHE . Results demonstrate that all four catalysts generate the over-hydrogenation product 4-aminoethylbenzene (4-AE), with Faradaic efficiencies (FE) ranging from 50% to 68% (Fig. 2 d, Figure S11). In contrast, the Pt/CNTs-AT PEES exhibits high selectivity (95.2%) toward 4-AS, and product selectivity gradually shifts from 4-AS to 4-NE as the hydrophobicity of CNTs increases. For the Pt/CNTs-C18 PEES, a 93.3% selectivity for 4-NE is achieved, and its FE is comparable to that of 4-AS in the Pt/CNTs-AT PEES (Fig. 2 d, Figure S12). Interestingly, the addition of inactive CNTs-C18 to the Pt/CNTs-AT PEES also enhances 4-NE selectivity from 0% to 35.7% (Figure S13), which corroborates the regulatory role of the biphasic microenvironment in product selectivity. To rule out the possibility of reactions occurring on the current collector, a control experiment was performed where Pt/CNTs-AT was coated onto the current collector and a Pickering emulsion stabilized by inactive CNTs-AT was employed (Figure S14). Under the same potential, this control system only exhibits a 3.6% FE (Figure S15), clearly confirming that the reaction primarily proceeds at the droplet interface rather than on the current collector surface. The origin of selectivity regulation at the interface To elucidate the influence of the biphasic microenvironment on the reaction, the dynamic distribution of 4-NS at the interface was first investigated via interfacial tension measurements. As illustrated in Fig. 3 a, 4 -NS exhibited surfactant-like behavior in the 0.5 M H₂SO₄ solution/cyclohexane system: the equilibrium interfacial tension decreased from 43.9 mN/m to 37.8 mN/m with increasing 4-NS concentration. After introducing Pt/CNTs-AT into the aqueous phase, the same trend of decreasing interfacial tension was observed, while the initial interfacial tension of this system was lower than that of the system without Pt/CNTs-AT. These results confirm that 4-NS tends to adsorb at the oil-water interface, and the presence of Pt/CNTs-AT further enhances this interfacial enrichment. Given that the thickness of the oil-water interfacial layer is merely a few molecular layers, we adopted the classical Gibbs model (Fig. 3 b) 23 , 24 , which approximates the actual interfacial layer as a segmented interface, to derive the relationship between the interfacial excess concentration (Γ) and interfacial tension in the system (Fig. 3 c). Calculations reveal that 4-NS achieves an interfacial excess of approximately 1.13×10⁻⁵ mmol/cm² under actual reaction conditions, which dynamically facilitates its interfacial reaction. Furthermore, we observed that the product selectivity in Pt/CNTs-C18 PEES exhibits a strong correlation with oil-water interfacial tension (Fig. 3 d, e). The selectivity for 4-NE declines with decreasing oil-water interfacial tension, dropping below 40% when ethyl acetate was used as the oil phase. A low interfacial tension is commonly indicative of strong intermolecular interactions between the two sides of the interface, making water molecules at the interface more prone to migrate into the opposite phase (Fig. 3 f) 23 , 25 . This phenomenon suggests that the selectivity regulation in PEES is related to proton accessibility within the interfacial layer. The composition of interfacial layers in different PEES was investigated by employing a spatially resolved Raman spectrometer to continuously collect Raman signals from the aqueous phase to the emulsion phase (Figure S16). As shown in Fig. 4 a, the intensity of the characteristic peak of water (3000–3800 cm⁻¹) gradually decreased as the focus spot moved across the water-emulsion boundary, while the cyclohexane peak (2800–3000 cm⁻¹) progressively increased. Given that the laser beam has an extremely thin penetration depth through CNTs at the interface (Figure S17), the obtained signal reflects the oil-water concentration distribution around the CNTs, namely the oil-water ratio (R = S₁/S₂) within the interfacial layer. Results indicate that the oil-water ratio at the droplet surface of Pt/CNTs-C18 PEES was significantly higher than that of Pt/CNTs-AT PEES (0.55 vs. 0.18), demonstrating that the introduction of hydrophobic CNTs-C18 remarkably altered the oil-water distribution on the three-dimensional conductive network. This finding is further supported by double-layer capacitance (C dl ) analysis via electrochemical impedance spectroscopy. C dl reflects the interfacial charge accumulation capacity and typically exhibits a positive correlation with ion accessibility. As shown in Fig. 4 b, the C dl value of Pt/CNTs-AT PEES consistently exceeded that of the current collector up to -0.5 V RHE and below. In contrast, the C dl of Pt/CNTs-C18 PEES remained lower than that of the current collector throughout the measurement range. According to Gouy-Chapman-Stern theory, the lower C dl in Pt/CNTs-C18 PEES can be attributed to the incorporation of oil into the double-layer region by hydrophobic Pt/CNTs-C18, which reduces the interfacial dielectric constant and thereby decreases the C dl (Figure S18) 26 – 29 . The presence of oil in the double layer would also suppress electron transfer processes and thereby affect the interfacial charge transfer resistance (R ct ). As expected, the R ct of Pt/CNTs-C18 PEES was as high as 1873 Ω at 0 V RHE , although it showed a decreasing trend with decreasing voltage (Fig. 4 c, Figure S19). In sharp contrast, Pt/CNTs-AT PEES exhibited minimal variation in R ct across the studied potential window (Figure S20). Notably, the selectivity of 4-NS hydrogenation in Pt/CNTs-C18 PEES undergoes a sudden switch at -0.4 V RHE , with more positive potentials resulting in high selectivity for 4-AS rather than 4-NE (Fig. 4 d). A similar switch was not observed in Pt/CNTs-AT PEES (Figure S21). This switching point was in good agreement with the potential at which the R ct of Pt/CNTs-C18 PEES reached the same level as that of Pt/CNTs-AT PEES, suggesting that under conditions of low proton accessibility, product selectivity is also governed by the electron transfer rate. To elaborate on the structural characteristics of interfacial layers, molecular dynamics (MD) simulations were employed to model the CNTs-C18 and CNTs-AT surfaces in a cyclohexane-water system (Fig. 5 a). Upon reaching equilibrium, all cyclohexane molecules aggregated near the CNTs-C18 side, whereas the CNTs-AT side retained almost no cyclohexane molecules. Analysis of the radial density distribution of different molecules revealed a unique water-oil-water sandwich structure formed on the CNTs-C18 surface (Fig. 5 b). This asymmetric distribution led to a more than tenfold reduction in the number of hydrogen bonds near the CNTs-C18 interface compared to the CNTs-AT interface (Fig. 5 c), which would significantly suppress proton transfer. Furthermore, Raman spectroscopy provides experimental support for the simulation results. By employing the non-negative minimum area difference method, the influence of bulk water was eliminated (Figure S22), thereby yielding residual signals characteristic of interfacial water at the droplet interface 30 . As shown in Fig. 5 d, the spectral band at 3000–3800 cm⁻¹ can be deconvoluted into three components according to previous reports 3 , 31 – 33 : strongly hydrogen-bonded water with four coordination sites (4HB-H₂O) at 3270 cm⁻¹, hydrogen-bonded water with two coordination sites (2HB-H₂O) at 3450 cm⁻¹, and free water at 3590 cm⁻¹. Compared to the planar oil-water interface, the 4HB-H₂O signal nearly disappeared in PEES, demonstrating that the presence of CNTs at the interface significantly disrupts the interfacial hydrogen-bonding network. Moreover, the 2HB-H₂O signal in the Pt/CNTs-C18 PEES system was weaker than that in Pt/CNTs-AT PEES, with more free water observed. This suggests a further weakening of the hydrogen-bonding network, presumably due to the presence of the oil layer as demonstrated by MD simulations. Collectively, these results indicate that proton accessibility at the Pt/CNTs-C18 surface is poorer than that at Pt/CNTs-AT surface. Systematic solvent effect experiments were performed to elucidate the critical role of protons in the competitive hydrogenation process. As shown in Fig. 6 a, in aprotic solvents (e.g., n-heptane, CH 2 Cl₂), the thermal catalytic hydrogenation of 4-NS preferentially occurred at the C = C bond; in protic solvents (e.g., ethanol, methanol), however, the catalyst exhibited enhanced activity toward the -NO₂ group. This solvent-dependent selectivity indicates that improved proton accessibility can shift the reaction pathway from C = C to -NO₂ hydrogenation. Moreover, the hydrogenation of both groups displayed Tafel slopes comparable to that of the HER (65.5–80.5 mV dec⁻¹), suggesting that both reactions involve a 1 e⁻ transfer process in the rate-determining step (Fig. 6 b). According to previous literature 29 , 34 , 35 , this 1 e⁻ transfer process can be attributed to either the Volmer step (single-electron transfer to H⁺ to generate adsorbed hydrogen species, H ads ) or a proton-coupled electron transfer (PCET) process. Further experimental results revealed that styrene exhibits a positive reaction order at low concentrations but a negative reaction order at higher concentrations (Fig. 6 c), consistent with a Langmuir-Hinshelwood mechanism, where reactant molecules and H ads species compete for adsorption sites. At higher styrene concentrations, the reaction rate decreases due to reduced H ads coverage. This result indicates that the hydrogenation of C = C double bonds primarily proceeds via a single-electron transfer process involving the Volmer step. This conclusion is reinforced by the significant kinetic isotope effect (KIE, k H /k D = 2.85) observed in styrene hydrogenation (Figure S23). In contrast, for the ECH of nitrobenzene, a positive reaction order is observed at lower concentrations, while approaching zero-order behavior at higher concentrations. This indicates that nitrobenzene reduction follows an Eley-Rideal mechanism, where reactivity increases with nitrobenzene coverage until surface saturation is achieved. This preliminary finding aligns with the characteristics of a PCET process. More direct evidence was obtained from electron-proton separation experiments 20 , 34 , 35 , where protons can flow through the proton exchange membrane while electron flow through the external circuit is monitored in real time (Fig. 6 d). Results showed that when no substrate or only styrene was added to the cathode compartment, the cell current remained extremely low with no product formation (Fig. 6 e). However, upon introducing nitrobenzene, the current increased significantly, and aniline products were detected at the cathode. This phenomenon indicates that separated protons and electrons cannot hydrogenate styrene but are effective for nitrobenzene, confirming that H ads species are required for C = C bond hydrogenation, whereas -NO₂ reduction can be completed via the separate and concurrent transfer of electrons and protons. Based on the above observations, the selectivity differences between the two PEES arise from their microstructural features at the droplet interface: In Pt/CNTs-AT PEES, the relatively intact interfacial hydrogen-bond network facilitates direct proton transfer to the -NO 2 group via a PCET process, resulting in high selectivity toward 4-AS. Conversely, in Pt/CNTs-C18 PEES, disruption of the hydrogen-bond network and alteration of the double-layer structure due to the hydrophobic environment block the PCET pathway and favor H ads formation, thereby promoting C = C bond hydrogenation (Fig. 6 f). Conclusion In summary, we show that the interfacial oil-water distribution in PEES can be precisely regulated by tuning the hydrophilicity/hydrophobicity of CNTs, thereby modulating the ECH selectivity of 4-NS. Hydrophilic Pt/CNTs-AT PEES achieves 95.2% selectivity for 4-AS via -NO 2 group reduction, while hydrophobic Pt/CNTs-C18 PEES exhibits 93.3% selectivity for 4-NE through C = C bond hydrogenation. Mechanistic studies reveal that the hydrophilic CNTs preserve an intact interfacial hydrogen-bond network, enabling efficient PCET process via the Eley-Rideal mechanism. In contrast, the hydrophobic support disrupts the hydrogen-bond network and alters the double-layer structure, promoting H ads formation via the Volmer step and subsequent C = C bond hydrogenation through the Langmuir-Hinshelwood mechanism. This work highlights the critical role of interfacial microenvironment engineering in controlling reaction pathways and provides a novel strategy for the selective synthesis of high-value chemicals in electrocatalytic hydrogenation systems. Declarations Competing Interests The authors declare no conflict of interest. Author Contributions Y.W. proposed the original idea, performed experimental work and data interpretation, and wrote the manuscript draft. L.L. participated in experimental work and data interpretation. Y.G. and X.Y. participated in supervision of the experimental work and in data interpretation. C.H. participated in the basic project definition and the conceptual planning of experimental work flow, supervised experimental work and contributed to data interpretation and writing of the manuscript. Acknowledgements The authors acknowledge financial support by the National Natural Science Foundation of China (22378212, 22168026, 22408182), the Natural Science Foundation of Inner Mongolia Autonomous Region (2025JQ029, 2023ZD09), and the Education Department of Inner Mongolia Autonomous Region (NJZZ23094, NJYT23039). Data Availability The data that support the findings of this study are available from the corresponding author upon reasonable request. References Zeng Y et al (2023) Recent progress in advanced catalysts for electrocatalytic hydrogenation of organics in aqueous conditions. eScience 3:100156 Liu C, Chen F, Zhao BH et al (2024) Electrochemical hydrogenation and oxidation of organic species involving water. Nat Rev Chem 8:277–293 Huang Y, Gao Y, Zhang B (2025) Interfacial water regulation for water-participating electrocatalytic hydrogenation reactions. Chem 11:102533 Kundu BK, Sun Y (2024) Electricity-driven organic hydrogenation using water as the hydrogen source. 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J Am Chem Soc 139:14120–14128 Additional Declarations There is NO Competing Interest. Supplementary Files HanetalSupportinginformation.docx Supporting information Cite Share Download PDF Status: Under Review 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-8332714","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":570508110,"identity":"94a373cf-16b7-4a85-b298-3e0bf0fc3700","order_by":0,"name":"Chenhui 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05:15:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8332714/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8332714/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":99755468,"identity":"06041020-9b1e-4f4b-b831-4de72dc582dd","added_by":"auto","created_at":"2026-01-08 05:27:26","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":9917738,"visible":true,"origin":"","legend":"","description":"","filename":"HanetalManuscript.docx","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/31d3da49114eeade0407c92b.docx"},{"id":99799007,"identity":"b9838795-ecc0-4c9d-925f-49b18696a76b","added_by":"auto","created_at":"2026-01-08 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05:27:27","extension":"png","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":628879,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/9590a7360b31603dbaab73e1.png"},{"id":99755483,"identity":"e8e0953f-10f9-421d-b419-8700a0941a00","added_by":"auto","created_at":"2026-01-08 05:27:27","extension":"xml","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":77804,"visible":true,"origin":"","legend":"","description":"","filename":"NCOMMS251000500structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/829616a6d99b8d1579b54be7.xml"},{"id":99798343,"identity":"c5ea8e7a-7867-4f12-96da-c1e54d4bf3d9","added_by":"auto","created_at":"2026-01-08 13:48:01","extension":"html","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":83966,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/f1a17ab76a14bf9b213a83fb.html"},{"id":99755465,"identity":"a20c67ac-7cf3-48a8-b160-9dc6d3ebc39b","added_by":"auto","created_at":"2026-01-08 05:27:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":630021,"visible":true,"origin":"","legend":"\u003cp\u003ePreparation and characterization of catalysts and Pickering emulsions. (a) Schematic illustration of the synthesis of CNT supports with varying hydrophilicity/hydrophobicity. (b) XPS spectra of Pt/CNTs-AT and Pt/CNTs-C18. TEM images of (c) Pt nanoparticles and (d) Pt/CNTs-AT catalyst. SEM images of freeze-dried Pickering emulsion droplets from (e-f) Pt/CNTs-AT PEES and (g) Pt/CNTs-C18 PEES.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/c52a467a117db046d91228bd.png"},{"id":99799393,"identity":"83347f30-463d-4061-af73-1325b85a03a8","added_by":"auto","created_at":"2026-01-08 13:49:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":290784,"visible":true,"origin":"","legend":"\u003cp\u003eElectrochemical characterization and the ECH of 4-NS. (a) Pictures of the customized cell and emulsion droplets. (b) PZC of the Ag current collector and different PEES. (c) LSV curves of Pt/CNTs-AT PEES and Pt/CNTs-C18 PEES in the absence (dashed lines) and presence (solid lines) of 30 mM 4-NS. (d) Comparison of product selectivity in different PEES and single-phase systems for the ECH of 4-NS.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/7f953e2f9c1855e6d25fe4e1.png"},{"id":99755467,"identity":"6410fe53-dcd1-4157-85f7-1c334320dcc0","added_by":"auto","created_at":"2026-01-08 05:27:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":186052,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of interfacial properties on reaction selectivity.\u003cstrong\u003e \u003c/strong\u003e(a) Water-cyclohexane interfacial tension as a function of 4-NS concentration.\u003cstrong\u003e \u003c/strong\u003e(b) Schematic comparison of the Gibbs model and the real oil-water interface.\u003cstrong\u003e \u003c/strong\u003e(c) Interfacial excess (Γ) of 4-NS at the oil-water interface as a function of 4-NS concentration.\u003cstrong\u003e \u003c/strong\u003e(d) Product selectivity in Pt/CNTs-C18 PEES using different oil phases.\u003cstrong\u003e \u003c/strong\u003e(e) Interfacial tension of different oil-water systems.\u003cstrong\u003e \u003c/strong\u003e(f) Schematic diagram of intermolecular interactions at the biphasic interface.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/b2afbdbf51c92ac77d1dc72b.png"},{"id":99755471,"identity":"cfc687f6-4e44-460b-9096-462acb66cc37","added_by":"auto","created_at":"2026-01-08 05:27:26","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":220458,"visible":true,"origin":"","legend":"\u003cp\u003eAnalysis of the Interface layer properties. (a) Spatially resolved Raman spectra of Pt/CNTs-AT PEES and Pt/CNTs-C18 PEES (b) Double-layer capacitance (C\u003csub\u003edl\u003c/sub\u003e) of Pt/CNTs-AT PEES, Pt/CNTs-C18 PEES, and the Ag current collector as a function of potential. (c) Interfacial charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e) of Pt/CNTs-AT PEES and Pt/CNTs-C18 PEES as a function of potential. (d) Product selectivity in Pt/CNTs-C18 PEES as a function of potential.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/38b2d174cce5e181a4fffdcf.png"},{"id":99799109,"identity":"df5d9e36-01a8-4d33-bb1c-f48c0c63a073","added_by":"auto","created_at":"2026-01-08 13:49:14","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":308281,"visible":true,"origin":"","legend":"\u003cp\u003eThe structural characteristics of interfacial layers. (a) MD simulation snapshots of CNTs-AT and CNTs-C18 surfaces in a cyclohexane-water system at different stages. (b) Radial density distribution of water and cyclohexane molecules. (c) Number of hydrogen bonds at the interface of CNTs-AT and CNTs-C18 over time. (d) Raman spectra of interfacial water in different systems.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/30b278c53b31a08b48e07bef.png"},{"id":99755470,"identity":"3bdd0c74-12a7-424f-af11-aacc54dc1c82","added_by":"auto","created_at":"2026-01-08 05:27:26","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":247383,"visible":true,"origin":"","legend":"\u003cp\u003eMechanistic studies on proton transfer and reaction pathways. (a) Solvent effect on the selectivity of 4-NS hydrogenation. (b) Tafel plots of HER, ECH of styrene and nitrobenzene. (c) Reaction orders for C=C and -NO\u003csub\u003e2\u003c/sub\u003e hydrogenation. (d) Schematic illustration of the electron-proton separation experiment setup. (e) Cell current under different conditions. (f) Schematic illustration of the proposed mechanism.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/93c1f56b2814f3c9c78b4493.png"},{"id":100356441,"identity":"439c253c-febf-4c2f-9356-4e98ecbc7518","added_by":"auto","created_at":"2026-01-16 07:09:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2158053,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/6b033774-b8bc-4a2d-b8a0-df90589808c2.pdf"},{"id":99755473,"identity":"d32bb53b-576c-4f55-8fc8-76c0fce3908e","added_by":"auto","created_at":"2026-01-08 05:27:26","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":14863157,"visible":true,"origin":"","legend":"Supporting information","description":"","filename":"HanetalSupportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-8332714/v1/4ca4b8533146069404dc528a.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Interfacial Microenvironment Engineering in Pickering Emulsion Electrocatalytic System for Selective Hydrogenation of 4-Nitrostyrene","fulltext":[{"header":"Introduction","content":"\u003cp\u003eElectrocatalytic hydrogenation (ECH) is a promising strategy for the hydrogenation of unsaturated substrates, where water serves as a sustainable hydrogen source\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. This technique has attracted considerable attention owing to its inherent advantages, including mild reaction conditions, low energy consumption, and high operational safety\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. However, a critical challenge limiting its efficiency lies in the poor solubility of most substrates in aqueous electrolytes, which severely restricts the accessibility of reactants to catalytic active sites. A rationally designed approach to address this limitation is to conduct ECH reactions directly at the oil-water interface, leveraging the unique microenvironment of this phase boundary to enhance reaction kinetics.\u003c/p\u003e \u003cp\u003eThe oil-water interface possesses distinct physicochemical properties, such as preferential molecular orientation\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, distinctive electron/ion transfer kinetics\u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, and ultrahigh reaction efficiency derived from microinterfacial effects\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. These features offer significant opportunities to optimize catalytic performance by precisely regulating the microenvironment surrounding catalytic active sites. Among various interfacial systems, Pickering emulsions stabilized by amphiphilic solid particles exhibit exceptional long-term stability, making them an ideal platform for the assembly of catalysts at the oil-water interface\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. In our previous work\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, we achieved efficient ECH of alkenes in an oil-in-water (O/W) Pickering emulsion electrocatalytic system (PEES), delivering a current density of 149 mA\u0026middot;mgPd⁻\u0026sup1; and a faradaic efficiency of 96%, significantly outperforming its conventional single-phase counterpart. However, the influence of the oil-water interfacial microenvironment on reaction selectivity remains elusive.\u003c/p\u003e \u003cp\u003eIn this study, we reveal a novel interfacial effect that is closely correlated with the oil-water distribution near catalytic sites. This effect significantly modulates the selectivity of the ECH of 4-nitrostyrene (4-NS) in PEES. Pt nanoparticles supported on hydrophilic carbon nanotubes (CNTs) exhibited high activity toward nitro group hydrogenation, achieving 95.2% selectivity for 4-aminostyrene (4-AS). In contrast, Pt nanoparticles supported on hydrophobic CNTs favored the hydrogenation of C\u0026thinsp;=\u0026thinsp;C bonds, with 93.3% selectivity for 4-nitroethylbenzene (4-NE). Through a combination of experimental investigations and computational simulations, we uncovered a previously unreported interfacial effect arising from the unique structure of the electric double layer and hydrogen-bonding interactions at the oil-water interface. This effect modulates hydrogen transfer pathways, selectively directing the reaction along either the Eley-Rideal or Langmuir-Hinshelwood mechanism\u003csup\u003e\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e to preferentially reduce nitro groups or C\u0026thinsp;=\u0026thinsp;C bonds, respectively.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003ePreparation and characterization of catalysts and Pickering emulsions\u003c/p\u003e \u003cp\u003eCNTs are ideal support materials for constructing PEES, owing to their high electrical conductivity and facile molecular functionalization. The synthesis protocols, nomenclature, and hydrophilic/hydrophobic properties of the four CNT supports investigated herein are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The as-received commercial CNTs exhibit a hydrophobic surface. Following acid treatment, their surface becomes hydrophilic due to the introduction of oxygen-containing functional groups (designated as CNTs-AT). Subsequent amidation reactions were performed to graft alkyl chains of varying lengths onto the surface of CNTs-AT, yielding CNTs-C8 and CNTs-C18 with distinct hydrophobicity. The resulting samples exhibited contact angles of 123.4\u0026deg; and 155.9\u0026deg;, respectively. Pre-synthesized monodisperse Pt nanoparticles (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) were then uniformly deposited onto the four supports to fabricate the corresponding catalysts (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e-2).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eX-ray photoelectron spectroscopy (XPS) analysis of the C 1s region revealed the disappearance of the O-C\u0026thinsp;=\u0026thinsp;O peak at 289.1 eV following amidation grafting (by comparing Pt/CNTs-AT and Pt/CNTs-C18), indicating that the carboxyl groups on CNTs-AT were involved in the amidation reaction (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Concomitantly, in the O 1s spectrum, the area of the C-O peak (at 533.4 eV) was significantly reduced, while a distinct N-H peak emerged in Pt/CNTs-C18 after grafting (Figure S3). These observations suggest that the carboxyl groups lose their -OH moieties to form C-N bonds during this process. Collectively, these results confirm the successful modification of CNTs with hydrophobic alkyl chains. For both Pt/CNTs-AT and Pt/CNTs-C18, the Pt 4f\u003csub\u003e5/2\u003c/sub\u003e and Pt 4f\u003csub\u003e7/2\u003c/sub\u003e peaks were detected at 75.1 eV and 71.7 eV\u003csup\u003e20\u003c/sup\u003e, respectively, indicating that Pt primarily exists in the metallic state and that its chemical state remains unaffected by the support.\u003c/p\u003e \u003cp\u003eAmong the four CNT candidates, CNTs-AT exhibited the optimal performance in stabilizing Pickering emulsions. Given that highly hydrophobic CNTs alone are incapable of stabilizing emulsions, CNTs-AT (without Pt nanoparticles) was added at a 1:1 ratio to the PEES of all four catalysts to assist emulsification (Figure S4). For example, the emulsion prepared with 5 mg of Pt/CNTs-C18 catalyst and 5 mg of CNTs-AT is designated as Pt/CNTs-C18 PEES. All four emulsions showed average droplet sizes in the range of 100\u0026ndash;200 \u0026micro;m (Figure S5). Scanning electron microscopy (SEM) images of freeze-dried PEES revealed an ultrathin (\u0026asymp;\u0026thinsp;40 nm, corresponding to 1\u0026ndash;2 layers of carbon nanotubes) three-dimensional interconnected network structure on the droplet surface stabilized by Pt/CNTs-AT (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee\u0026ndash;f). In contrast, the Pt/CNTs-C18 emulsion formed a denser, slightly thicker network with clear interconnections between droplets (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg, Figure S6). This interconnected state ensures electron transfer across droplets at the oil-water interface. The aggregation of CNTs on droplet surfaces was further verified by droplet solidification technology\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e and confocal laser scanning microscopy (CLSM) (Figure S7-9). This interfacial assembly behavior ensures the localization of Pt nanoparticles near the oil-water interface of the droplets.\u003c/p\u003e \u003cp\u003eSelectivity regulatory behavior on the PEES interface\u003c/p\u003e \u003cp\u003eElectrochemical tests were performed in a customized reactor (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) adopting a three-electrode configuration analogous to an H-type cell, where the cathode and anode compartments were separated by a Nafion 117 membrane. The cathode compartment was filled with Pickering emulsion, and an annular Ag foil (5 cm\u0026sup2;) was inserted into the emulsion phase to serve as the current collector. A homogenizer mounted at the top of the cathode compartment could operate intermittently to eliminate concentration gradients and enhance mass transfer. The potential of zero charge (PZC) of the Ag current collector reflects its surface charge property in the electrolyte, corresponding to the potential at which the differential capacitance reaches a minimum. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, the PZC of the Ag current collector was determined to be -0.45 V\u003csub\u003eRHE\u003c/sub\u003e, indicating that its surface maintains a positive charge until the applied potential shifts to a value more negative than \u0026minus;\u0026thinsp;0.45 V\u003csub\u003eRHE\u003c/sub\u003e. In the Pt/CNTs-AT and Pt/CNTs-C18 PEES, the emulsion droplets stabilized by negatively charged CNTs-AT (Figure S10) were adsorbed onto the current collector and neutralized its surface charge, thereby shifting the PZC of the current collector to a value near zero. This phenomenon implies the formation of an electrical connection between the CNTs and the current collector, which facilitates electron transfer to the CNTs at the oil-water interface for catalyzing the reactions therein.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eLinear sweep voltammetry (LSV) curves of two representative PEES in 0.5 M H₂SO₄ electrolyte demonstrate that both the hydrophilic (Pt/CNTs-AT PEES) and hydrophobic (Pt/CNTs-C18 PEES) systems exhibit nearly identical onset potentials for the hydrogen evolution reaction (HER) (dashed lines, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). In contrast, in the presence of 4-NS, the Pt/CNTs-AT PEES shows a considerably lower onset potential than the Pt/CNTs-C18 PEES (solid lines). This result indicates that the interfacial environment, not merely the catalyst alone, exerts a significant influence on the hydrogenation process of 4-NS. Furthermore, the onset potentials in the presence of 4-NS are lower than those in its absence, suggesting that the electrocatalytic reduction of 4-NS is thermodynamically more favorable than that of HER.\u003c/p\u003e \u003cp\u003eECH of 4-NS was first investigated in a single-phase system at -0.4 V\u003csub\u003eRHE\u003c/sub\u003e. Results demonstrate that all four catalysts generate the over-hydrogenation product 4-aminoethylbenzene (4-AE), with Faradaic efficiencies (FE) ranging from 50% to 68% (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, Figure S11). In contrast, the Pt/CNTs-AT PEES exhibits high selectivity (95.2%) toward 4-AS, and product selectivity gradually shifts from 4-AS to 4-NE as the hydrophobicity of CNTs increases. For the Pt/CNTs-C18 PEES, a 93.3% selectivity for 4-NE is achieved, and its FE is comparable to that of 4-AS in the Pt/CNTs-AT PEES (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, Figure S12). Interestingly, the addition of inactive CNTs-C18 to the Pt/CNTs-AT PEES also enhances 4-NE selectivity from 0% to 35.7% (Figure S13), which corroborates the regulatory role of the biphasic microenvironment in product selectivity. To rule out the possibility of reactions occurring on the current collector, a control experiment was performed where Pt/CNTs-AT was coated onto the current collector and a Pickering emulsion stabilized by inactive CNTs-AT was employed (Figure S14). Under the same potential, this control system only exhibits a 3.6% FE (Figure S15), clearly confirming that the reaction primarily proceeds at the droplet interface rather than on the current collector surface.\u003c/p\u003e \u003cp\u003eThe origin of selectivity regulation at the interface\u003c/p\u003e \u003cp\u003eTo elucidate the influence of the biphasic microenvironment on the reaction, the dynamic distribution of 4-NS at the interface was first investigated via interfacial tension measurements. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e-NS exhibited surfactant-like behavior in the 0.5 M H₂SO₄ solution/cyclohexane system: the equilibrium interfacial tension decreased from 43.9 mN/m to 37.8 mN/m with increasing 4-NS concentration. After introducing Pt/CNTs-AT into the aqueous phase, the same trend of decreasing interfacial tension was observed, while the initial interfacial tension of this system was lower than that of the system without Pt/CNTs-AT. These results confirm that 4-NS tends to adsorb at the oil-water interface, and the presence of Pt/CNTs-AT further enhances this interfacial enrichment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGiven that the thickness of the oil-water interfacial layer is merely a few molecular layers, we adopted the classical Gibbs model (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb)\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, which approximates the actual interfacial layer as a segmented interface, to derive the relationship between the interfacial excess concentration (Γ) and interfacial tension in the system (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Calculations reveal that 4-NS achieves an interfacial excess of approximately 1.13\u0026times;10⁻⁵ mmol/cm\u0026sup2; under actual reaction conditions, which dynamically facilitates its interfacial reaction.\u003c/p\u003e \u003cp\u003eFurthermore, we observed that the product selectivity in Pt/CNTs-C18 PEES exhibits a strong correlation with oil-water interfacial tension (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, e). The selectivity for 4-NE declines with decreasing oil-water interfacial tension, dropping below 40% when ethyl acetate was used as the oil phase. A low interfacial tension is commonly indicative of strong intermolecular interactions between the two sides of the interface, making water molecules at the interface more prone to migrate into the opposite phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef)\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. This phenomenon suggests that the selectivity regulation in PEES is related to proton accessibility within the interfacial layer.\u003c/p\u003e \u003cp\u003eThe composition of interfacial layers in different PEES was investigated by employing a spatially resolved Raman spectrometer to continuously collect Raman signals from the aqueous phase to the emulsion phase (Figure S16). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, the intensity of the characteristic peak of water (3000\u0026ndash;3800 cm⁻\u0026sup1;) gradually decreased as the focus spot moved across the water-emulsion boundary, while the cyclohexane peak (2800\u0026ndash;3000 cm⁻\u0026sup1;) progressively increased. Given that the laser beam has an extremely thin penetration depth through CNTs at the interface (Figure S17), the obtained signal reflects the oil-water concentration distribution around the CNTs, namely the oil-water ratio (R\u0026thinsp;=\u0026thinsp;S₁/S₂) within the interfacial layer. Results indicate that the oil-water ratio at the droplet surface of Pt/CNTs-C18 PEES was significantly higher than that of Pt/CNTs-AT PEES (0.55 vs. 0.18), demonstrating that the introduction of hydrophobic CNTs-C18 remarkably altered the oil-water distribution on the three-dimensional conductive network.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis finding is further supported by double-layer capacitance (C\u003csub\u003edl\u003c/sub\u003e) analysis via electrochemical impedance spectroscopy. C\u003csub\u003edl\u003c/sub\u003e reflects the interfacial charge accumulation capacity and typically exhibits a positive correlation with ion accessibility. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, the C\u003csub\u003edl\u003c/sub\u003e value of Pt/CNTs-AT PEES consistently exceeded that of the current collector up to -0.5 V\u003csub\u003eRHE\u003c/sub\u003e and below. In contrast, the C\u003csub\u003edl\u003c/sub\u003e of Pt/CNTs-C18 PEES remained lower than that of the current collector throughout the measurement range. According to Gouy-Chapman-Stern theory, the lower C\u003csub\u003edl\u003c/sub\u003e in Pt/CNTs-C18 PEES can be attributed to the incorporation of oil into the double-layer region by hydrophobic Pt/CNTs-C18, which reduces the interfacial dielectric constant and thereby decreases the C\u003csub\u003edl\u003c/sub\u003e (Figure S18)\u003csup\u003e\u003cspan additionalcitationids=\"CR27 CR28\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe presence of oil in the double layer would also suppress electron transfer processes and thereby affect the interfacial charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e). As expected, the R\u003csub\u003ect\u003c/sub\u003e of Pt/CNTs-C18 PEES was as high as 1873 Ω at 0 V\u003csub\u003eRHE\u003c/sub\u003e, although it showed a decreasing trend with decreasing voltage (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, Figure S19). In sharp contrast, Pt/CNTs-AT PEES exhibited minimal variation in R\u003csub\u003ect\u003c/sub\u003e across the studied potential window (Figure S20). Notably, the selectivity of 4-NS hydrogenation in Pt/CNTs-C18 PEES undergoes a sudden switch at -0.4 V\u003csub\u003eRHE\u003c/sub\u003e, with more positive potentials resulting in high selectivity for 4-AS rather than 4-NE (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). A similar switch was not observed in Pt/CNTs-AT PEES (Figure S21). This switching point was in good agreement with the potential at which the R\u003csub\u003ect\u003c/sub\u003e of Pt/CNTs-C18 PEES reached the same level as that of Pt/CNTs-AT PEES, suggesting that under conditions of low proton accessibility, product selectivity is also governed by the electron transfer rate.\u003c/p\u003e \u003cp\u003eTo elaborate on the structural characteristics of interfacial layers, molecular dynamics (MD) simulations were employed to model the CNTs-C18 and CNTs-AT surfaces in a cyclohexane-water system (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). Upon reaching equilibrium, all cyclohexane molecules aggregated near the CNTs-C18 side, whereas the CNTs-AT side retained almost no cyclohexane molecules. Analysis of the radial density distribution of different molecules revealed a unique water-oil-water sandwich structure formed on the CNTs-C18 surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). This asymmetric distribution led to a more than tenfold reduction in the number of hydrogen bonds near the CNTs-C18 interface compared to the CNTs-AT interface (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec), which would significantly suppress proton transfer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, Raman spectroscopy provides experimental support for the simulation results. By employing the non-negative minimum area difference method, the influence of bulk water was eliminated (Figure S22), thereby yielding residual signals characteristic of interfacial water at the droplet interface\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed, the spectral band at 3000\u0026ndash;3800 cm⁻\u0026sup1; can be deconvoluted into three components according to previous reports\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e: strongly hydrogen-bonded water with four coordination sites (4HB-H₂O) at 3270 cm⁻\u0026sup1;, hydrogen-bonded water with two coordination sites (2HB-H₂O) at 3450 cm⁻\u0026sup1;, and free water at 3590 cm⁻\u0026sup1;. Compared to the planar oil-water interface, the 4HB-H₂O signal nearly disappeared in PEES, demonstrating that the presence of CNTs at the interface significantly disrupts the interfacial hydrogen-bonding network. Moreover, the 2HB-H₂O signal in the Pt/CNTs-C18 PEES system was weaker than that in Pt/CNTs-AT PEES, with more free water observed. This suggests a further weakening of the hydrogen-bonding network, presumably due to the presence of the oil layer as demonstrated by MD simulations. Collectively, these results indicate that proton accessibility at the Pt/CNTs-C18 surface is poorer than that at Pt/CNTs-AT surface.\u003c/p\u003e \u003cp\u003eSystematic solvent effect experiments were performed to elucidate the critical role of protons in the competitive hydrogenation process. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, in aprotic solvents (e.g., n-heptane, CH\u003csub\u003e2\u003c/sub\u003eCl₂), the thermal catalytic hydrogenation of 4-NS preferentially occurred at the C\u0026thinsp;=\u0026thinsp;C bond; in protic solvents (e.g., ethanol, methanol), however, the catalyst exhibited enhanced activity toward the -NO₂ group. This solvent-dependent selectivity indicates that improved proton accessibility can shift the reaction pathway from C\u0026thinsp;=\u0026thinsp;C to -NO₂ hydrogenation. Moreover, the hydrogenation of both groups displayed Tafel slopes comparable to that of the HER (65.5\u0026ndash;80.5 mV dec⁻\u0026sup1;), suggesting that both reactions involve a 1 e⁻ transfer process in the rate-determining step (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). According to previous literature\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, this 1 e⁻ transfer process can be attributed to either the Volmer step (single-electron transfer to H⁺ to generate adsorbed hydrogen species, H\u003csub\u003eads\u003c/sub\u003e) or a proton-coupled electron transfer (PCET) process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurther experimental results revealed that styrene exhibits a positive reaction order at low concentrations but a negative reaction order at higher concentrations (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec), consistent with a Langmuir-Hinshelwood mechanism, where reactant molecules and H\u003csub\u003eads\u003c/sub\u003e species compete for adsorption sites. At higher styrene concentrations, the reaction rate decreases due to reduced H\u003csub\u003eads\u003c/sub\u003e coverage. This result indicates that the hydrogenation of C\u0026thinsp;=\u0026thinsp;C double bonds primarily proceeds via a single-electron transfer process involving the Volmer step. This conclusion is reinforced by the significant kinetic isotope effect (KIE, k\u003csub\u003eH\u003c/sub\u003e/k\u003csub\u003eD\u003c/sub\u003e = 2.85) observed in styrene hydrogenation (Figure S23). In contrast, for the ECH of nitrobenzene, a positive reaction order is observed at lower concentrations, while approaching zero-order behavior at higher concentrations. This indicates that nitrobenzene reduction follows an Eley-Rideal mechanism, where reactivity increases with nitrobenzene coverage until surface saturation is achieved. This preliminary finding aligns with the characteristics of a PCET process.\u003c/p\u003e \u003cp\u003eMore direct evidence was obtained from electron-proton separation experiments\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, where protons can flow through the proton exchange membrane while electron flow through the external circuit is monitored in real time (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). Results showed that when no substrate or only styrene was added to the cathode compartment, the cell current remained extremely low with no product formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee). However, upon introducing nitrobenzene, the current increased significantly, and aniline products were detected at the cathode. This phenomenon indicates that separated protons and electrons cannot hydrogenate styrene but are effective for nitrobenzene, confirming that H\u003csub\u003eads\u003c/sub\u003e species are required for C\u0026thinsp;=\u0026thinsp;C bond hydrogenation, whereas -NO₂ reduction can be completed via the separate and concurrent transfer of electrons and protons.\u003c/p\u003e \u003cp\u003eBased on the above observations, the selectivity differences between the two PEES arise from their microstructural features at the droplet interface: In Pt/CNTs-AT PEES, the relatively intact interfacial hydrogen-bond network facilitates direct proton transfer to the -NO\u003csub\u003e2\u003c/sub\u003e group via a PCET process, resulting in high selectivity toward 4-AS. Conversely, in Pt/CNTs-C18 PEES, disruption of the hydrogen-bond network and alteration of the double-layer structure due to the hydrophobic environment block the PCET pathway and favor H\u003csub\u003eads\u003c/sub\u003e formation, thereby promoting C\u0026thinsp;=\u0026thinsp;C bond hydrogenation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we show that the interfacial oil-water distribution in PEES can be precisely regulated by tuning the hydrophilicity/hydrophobicity of CNTs, thereby modulating the ECH selectivity of 4-NS. Hydrophilic Pt/CNTs-AT PEES achieves 95.2% selectivity for 4-AS via -NO\u003csub\u003e2\u003c/sub\u003e group reduction, while hydrophobic Pt/CNTs-C18 PEES exhibits 93.3% selectivity for 4-NE through C\u0026thinsp;=\u0026thinsp;C bond hydrogenation. Mechanistic studies reveal that the hydrophilic CNTs preserve an intact interfacial hydrogen-bond network, enabling efficient PCET process via the Eley-Rideal mechanism. In contrast, the hydrophobic support disrupts the hydrogen-bond network and alters the double-layer structure, promoting H\u003csub\u003eads\u003c/sub\u003e formation via the Volmer step and subsequent C\u0026thinsp;=\u0026thinsp;C bond hydrogenation through the Langmuir-Hinshelwood mechanism. This work highlights the critical role of interfacial microenvironment engineering in controlling reaction pathways and provides a novel strategy for the selective synthesis of high-value chemicals in electrocatalytic hydrogenation systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting Interests\u003c/h2\u003e \u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\u003ch2\u003eAuthor Contributions\u003c/h2\u003e \u003cp\u003eY.W. proposed the original idea, performed experimental work and data interpretation, and wrote the manuscript draft. L.L. participated in experimental work and data interpretation. Y.G. and X.Y. participated in supervision of the experimental work and in data interpretation. C.H. participated in the basic project definition and the conceptual planning of experimental work flow, supervised experimental work and contributed to data interpretation and writing of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors acknowledge financial support by the National Natural Science Foundation of China (22378212, 22168026, 22408182), the Natural Science Foundation of Inner Mongolia Autonomous Region (2025JQ029, 2023ZD09), and the Education Department of Inner Mongolia Autonomous Region (NJZZ23094, NJYT23039).\u003c/p\u003e\n\u003ch3\u003eData Availability\u003c/h3\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eZeng Y et al (2023) Recent progress in advanced catalysts for electrocatalytic hydrogenation of organics in aqueous conditions. eScience 3:100156\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu C, Chen F, Zhao BH et al (2024) Electrochemical hydrogenation and oxidation of organic species involving water. 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J Am Chem Soc 139:14120\u0026ndash;14128\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"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":"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-8332714/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8332714/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTuning reaction selectivity by modifying the microenvironment around active sites is an intriguing research focus in catalysis. Here, we show that the selectivity of 4-nitrostyrene hydrogenation can be modulated via interfacial microenvironment engineering in a Pickering emulsion electrocatalytic system, where an interfacial effect derived from the unique structure of the electric double layer and interfacial hydrogen-bonding interactions steers the hydrogen transfer pathway. Specifically, hydrophilic Pt/CNTs-AT preserves the intact interfacial hydrogen-bond network, facilitating efficient proton-coupled electron transfer that preferentially reduces the nitro group, thus achieving 95.2% selectivity for 4-aminostyrene. In contrast, hydrophobic Pt/CNTs-C18 disrupts the hydrogen-bond network and alters the electric double layer structure, promoting the formation of adsorbed hydrogen and thus directing the reaction toward C\u0026thinsp;=\u0026thinsp;C bond hydrogenation, with 93.3% selectivity for 4-nitroethylbenzene. This work provides new insights into the selective hydrogenation of multifunctional substrates, highlighting the critical role of interfacial microenvironment regulation in steering reaction pathways.\u003c/p\u003e","manuscriptTitle":"Interfacial Microenvironment Engineering in Pickering Emulsion Electrocatalytic System for Selective Hydrogenation of 4-Nitrostyrene","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-08 05:27:21","doi":"10.21203/rs.3.rs-8332714/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"21a92573-f854-4e04-9972-0303a60d7222","owner":[],"postedDate":"January 8th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":60707425,"name":"Physical sciences/Chemistry/Electrochemistry/Electrocatalysis"},{"id":60707426,"name":"Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis"},{"id":60707427,"name":"Physical sciences/Chemistry/Catalysis/Catalytic mechanisms"},{"id":60707428,"name":"Physical sciences/Materials science/Soft materials/Colloids"}],"tags":[],"updatedAt":"2026-04-07T10:43:06+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-08 05:27:21","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8332714","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8332714","identity":"rs-8332714","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}