Mixed Electron–Proton Conductors Enable Spatial Separation of Bond Activation and Charge Transfer in Electrocatalysis

Electrochemical energy conversion requires electrodes that can simultaneously facilitate substrate bond activation and electron–proton charge transfer. Traditional electrodes co-localize both functions to a single solid|liquid interface even though each process is typically favored in a disparate reaction environment. Herein, we establish a strategy for spatially separating bond activation and charge transfer by exploiting mixed electron–proton conduction (MEPC) in an oxide membrane. Specifically, we interpose a MEPC WO x membrane between a Pt catalyst and aqueous electrolyte and show that this composite electrode is active for the hydrogen oxidation reaction (HOR). Consistent with H 2 activation occurring at the gas|solid interface, the composite electrode displays HOR current densities over 8-fold larger than the diffusion-limited rate of HOR catalysis at a singular Pt|solution interface. The segregation of bond activation and charge separation steps also confers excellent tolerance to poisons and impurities introduced to the electrolyte. Mechanistic studies establish that H 2 activation at the Pt|gas interface is coupled to the electron–proton charge separation at the WO x |solution interface via rapid H-diffusion in the bulk of the WO x . Consequently, the rate of HOR is principally controlled by the rate of H-spillover at the Pt|WO x boundary. Our results establish MEPC membrane electrodes as a platform for spatially separating the critical bond activation and charge transfer steps of electrocatalysis.