Electric-field enhanced water-dissociation catalysis on oxide surfaces

Abstract

Ion-transfer reactions in the presence of electric fields are ubiquitous in (bio/electro)chemical systems and catalysis, yet the impact of the electric field is poorly understood. Here, we use bipolar membranes (BPMs) to isolate electric-field-driven non-faradaic water dissociation (WD: H2O → H+ + OH−) on catalytic surfaces. We find the catalyst layer's ionic properties dictate both the transport and kinetic processes within the BPM. The role of these properties are explored via a series of membrane architectures, and catalyst poisoning experiments, and the corresponding current–voltage and impedance responses. Arrhenius analyses show that an acidic graphene-oxide (GOx) catalyst layer gives rise to low interfacial H2O entropy in the heterojunction, illustrated via a >100 fold increase in the Arrhenius prefactor relative to baseline TiO2 measurements. Furthermore, ∼50% of the applied driving force goes towards reducing the apparent enthalpic activation barrier in the case of GOx, while other metal-oxide catalysts have enthalpic barriers independent of driving force. This analysis demonstrates a new mechanistic understanding of WD, where local electric fields augment enthalpic transition-state barriers, and the local ionic environment facilitates field-driven ion transfer. Ultimately, these results present a new design space for designing ion-transfer catalytic processes, and ionic heterojunctions more broadly.