Recent Progress in Decoupled H2 and O2 Production from Electrolytic Water Splitting

Abstract Conventional water splitting electrolyzers produce H2 and O2 simultaneously and, thus, result in the potential formation of a hazardous H2/O2 mixture and reactive oxygen species, posing safety risks and substantially increasing the manufacturing cost of electrolyzers. The use of redox mediators successfully decouples water splitting to generate H2 and O2 at different times and in different places. Such a nonconventional water splitting strategy enables the possibility of producing highly pure gas products. In some cases, the costly membrane could also be avoided. Even though it is a relatively new field, many promising electrocatalytic and photocatalytic systems have been reported over the last few years for decoupled water splitting. This Minireview briefly introduces the design principle and highlights several representative redox mediators of decoupled water‐splitting electrolysis. It is anticipated that new competent and low‐cost redox mediators will be developed not only for water electrolysis, but also many other renewable energy‐driven applications.