Recent Progress in Decoupled H 2 and O 2 Production from Electrolytic Water Splitting

Abstract Conventional water splitting electrolyzers produce H 2 and O 2 simultaneously and, thus, result in the potential formation of a hazardous H 2 /O 2 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 H 2 and O 2 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.