Advanced Device Architecture Strategies for Decoupled Water Splitting: A Review

Electrochemical water-splitting processes are a safe, sustainable, and ecofriendly method to generate pure hydrogen, with minimal carbon emission. Typically, water reduction (hydrogen evolution) and oxidation (oxygen evolution) occur simultaneously, although such coupled processes lead to several limitations such as gas crossover, electrocatalyst degradation by reactive oxygen species, and more. This review presents several strategies to design decoupled water splitting devices, separating the two half-reactions spatially and temporally, to address several of these issues. The designs change according to the electrode materials, electrolyte, and decoupling strategy employed (redox mediator). The review describes how the decoupling mechanisms adopted affect different properties and lead to designs with optimal efficiency. It also focuses on their integration with renewable energy, which can be used to power each half-reaction independently. Lastly, the merits and constraints of the decoupled systems in addressing global environmental issues are discussed along with potential questions to further advance this technology-based strategy.