A High-Rate Electrode with Grotthuss Topochemistry for Membrane-Free Decoupled Acid Water Electrolysis

Water electrolysis powered by renewable energies is regarded as the most promising technology for hydrogen production. However, in conventional acid water electrolysis, the H-2 production and O-2 production are tightly coupled and the proton exchange membrane is required to prevent the gases mixing, which reduce the flexibility of this technology and increase its cost. Here, a low-cost hydrated Prussian blue analog (Turnbull's blue) electrode is introduced as a solid-state redox mediator to decouple the acid water electrolysis into two steps without the use of membrane. The redox mediator shows high-rate performance (42.7 mAh g(-1) at 120 A g(-1)) and long cycle life (5000 cycles), which is owing to the diffusion-free Grotthuss proton conduction. Moreover, this decoupled water electrolysis device facilitates the utilization of renewable energies for high-purity hydrogen production at different spaces and times, which shows the high flexibility for H-2 production.