Solid‐State Redox Mediators for Decoupled H2 Production: Principle and Challenges

Abstract Water splitting driven by renewable energy is considered to be a promising approach for sustainable H 2 production. However, the simultaneous generation of H 2 and O 2 requires the use of a membrane to prevent the gas mixing, which significantly limits the flexibility of H 2 /O 2 separation and H 2 transportation, impeding the direct use of renewable sources. In recent years, the concept of decoupled water electrolysis has been proposed along with the utilization of solid‐state redox mediators, by which the H 2 and O 2 generated at different times and spaces could be separated in absence of membrane. Here, a comprehensive overview of the decoupled water electrolysis using solid‐state redox mediators (SRMs) is presented. After a brief introduction, the SRMs are systematically summarized, including the structural features, the reaction mechanisms, and the properties of decoupled systems. In addition, the coupling of decoupled hydrogen production with other valuable reactions is also involved. Finally, this work discusses the challenges and perspectives for the decoupled water splitting system for commercialization and sustainable H 2 production.