Decoupled Water Reduction and Hydrazine Oxidation by Fast Proton Transport MoO3 Redox Mediator for Hydrogen Production.

Water electrolysis powered by renewable energy is a green and sustainable method for hydrogen production. Decoupled water electrolysis with the aid of solid-state redox mediator could separate the hydrogen and oxygen production in time and space without the use of the membrane, showing high flexibility. Herein, a MoO₃ electrode with fast proton transport property is employed as a solid-state redox mediator to construct a membrane-free decoupled acidic electrolytic system. The MoO₃ electrode exhibits high specific capacity (204.3 mAh g^-1 at 5 A g^-1) and excellent rate performance (92.8 mAh g^-1 at 150 A g^-1) in the acidic environment. Due to the dense oxide-ion arrays, MoO₃ still exhibits excellent performance under high mass-loading. In addition, a hybrid decoupled electrolysis system is also constructed by combining water reduction and hydrazine oxidation, which can not only generate high-purity H₂ but also remove hydrazine hazards in acidic wastewater with lower energy consumption.