Electrolysis without electrodes: thermodynamic and kinetic insights into decoupled alkaline water electrolysis

Conventional water electrolysis is fundamentally limited by the kinetic constraints of coupled electrode reactions, particularly the oxygen evolution reaction, which necessitate substantial overpotentials despite decades of catalyst development. Recently, spatially and temporally decoupled electrolysis has emerged as a new paradigm in which electrochemical charge storage and catalytic fuel production are separated. This decoupling enables catalysis beyond the confines of the electrode surface and fundamentally alters how electrons are delivered to the catalyst. Here, we investigate redox-mediated hydrogen evolution in strongly alkaline media, examining the interplay between dissolved redox mediators and heterogeneous hydrogen evolution catalysts. Notably, we demonstrate that separating electron transfer from catalytic hydrogen evolution minimises some of the kinetic penalty associated with the electrode-electrolyte interface, enabling hydrogen evolution at potentials approaching the thermodynamic limit, even on nickel catalysts. Nevertheless, catalyst identity remains critical in determining reaction kinetics. Comparison of platinum and Raney® nickel reveals a prolonged activation period unique to nickel, demonstrating that catalyst surface chemistry continues to govern hydrogen evolution despite the absence of direct electrode-mediated electron transfer. These findings establish decoupled electrolysis as a fundamentally distinct model for investigating the interplay between charge transfer and catalysis, providing new insight into electrocatalytic energy conversion.