Breaking boundaries: advancements in solid-state redox mediators for decoupled water electrolysis

Abstract

Hydrogen (H₂) production from water electrolysis provides a reliable route to accelerated decarbonization. Most of the studies in the past have focused on high-performance electrocatalysts, and there have been few innovations in water electrolytic systems. In conventional water electrolysis processes, the gaseous products mix to some extent inevitably, which poses an inherent challenge in terms of economics and operating costs. In this context, the use of redox mediators (RMs) for decoupled water electrolysis was first proposed in 2013 to completely separate the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in spatial and temporal terms. Among them, the realization of soluble RMs requires the introduction of a proton exchange membrane as well as a driving system, which raises technical issues and even limits the energy conversion efficiency. A solid-state RM decoupling system can overcome the above limitations and has received increasing attention. Herein, we review the recent progress of solid-state RMs for decoupled water electrolysis in different electrolytes. Specifically, we discuss the advantages and challenges of the current solid-state decoupled water electrolysis technologies and offer some perspectives on future developments.