Highly efficient conversion of surplus electricity to hydrogen energy via polysulfides redox.

Decoupled electrolysis of water is a promising strategy for peak load regulation of electricity. The key to developing this technology is to construct decoupled devices containing stable redox mediators and corresponding efficient catalysts, which remains a considerable challenge. Herein, we designed a high-performance device, using polysulfides as mediators and graphene-encapsulated CoNi as catalysts. It produced H2 with a low potential of 0.82 V at 100 mA/cm2, saving 60.2% more energy than direct water electrolysis. The capacity of H2 production reached 2.5×105 mAh/cm2, which is the highest capacity reported so far. This device exhibited excellent cyclability in 15-day recycle tests, without any decay of performance. The calculation results revealed that the electronic structure of the graphene shell was modulated by the electron transfer from N-dopant and metal core, which significantly facilitated recycle of polysulfides on graphene surfaces. This study provides a promising method for constructing a smart grid by developing efficient decoupled devices.