Redox-Mediated Water Splitting for Decoupled H2 Production

Green H2 production from\nrenewable energy sources by\nwater splitting is desired to reduce the use of fossil fuels and CO2 emissions. The past decade has witnessed the fast development\nof electrolytic water splitting for H2 generation, with\nmost of the studies focusing on the development of superior electrocatalysts\nfor hydrogen evolution reaction (HER) and oxygen evolution reaction\n(OER). Equally important is the innovation of water splitting system\ndesign to tackle the critical issues confronted by conventional water\nelectrolysis. Some interesting developments have recently emerged\nwith additional redox-mediated process to separate the HER and OER\nin time and space. In this Review, the various strategies for decoupled\nH2 production are critically reviewed. Based on the additional\nprocess, which is introduced in conjunction with the electrochemical\nprocess for decoupled electrochemical or chemical H2 production,\nthe distinct operating principle is highlighted for each strategy,\nand the underlying connections to other strategies are delineated.\nLastly, the implications of the decoupled operations in addressing\nthe formidable issues of conventional water electrolysis, their inherent\nconstraints for practical implementation, and potential solutions\nare broadly discussed.