Decoupled alkaline water electrolysis by a K_0.5MnO₂-Ti mediator via K-ion insertion/extraction

Conventional one-step water electrolyzers generate H₂ accompanied by O₂ evolution, and may cause gas mixing and high cell voltage inputs. Herein, using the potassium ion battery material of K_0.5MnO₂-Ti as a mediator, we effectively decoupled the H₂ and O₂ evolution of alkaline water electrolysis temporally, thereby achieving a membrane-free pathway for H₂ production. As a mediator electrode for charge storage, the K_0.5MnO₂-Ti exhibited a stable capacity of 100 mA h g^-1 at 0.1 A g^-1 owing to the reversible K-ion insertion/extraction mechanism. The decoupled water electrolysis device exhibited the step voltages for hydrogen and oxygen production of 1.02 and 0.57 V at 5 mA, respectively. A nearly unity Faradaic efficiency and sustained production of pure H₂ has been demonstrated at a constant current density. We anticipate that this mediator demonstrated here may provide a route for the practical application of the decoupling strategy.