Decoupled water electrolysis for efficient membrane-free H2-production using an enhanced thermally-renewable Co-Ni(OH)2/MWNTs auxiliary electrode

Decoupled water electrolysis both spatially and temporally, is a promising path for H2-production, offering advantages such as higher overall efficiency, increased flexibility, cost savings, and better load management. The key to this is an efficient auxiliary electrode acting as a redox mediator. Here, the high performance of a novel cobalt-doped nickel hydroxide auxiliary electrode (Co-Ni(OH)2/MWNTs) is reported. We demonstrate that the synergetic effect of cobalt doping and the introduction of MWNTs improves the charge capacity, rate performance, and redox potential window of the auxiliary electrodes while maintaining favorable cycling stability. The auxiliary electrodes reach a high areal capacitance of 34.44 F cm−2 for two-step electrochemical cycles with a long-lasting H2/O2 production duration of 1860 s at 10 mA cm−2. The necessary voltage requirement (1.636 V) of the overall water electrolysis is broken into two smaller ones, 1.404 and 0.268 V, for H2 and O2 production, respectively. Notably, our auxiliary electrodes enable a spontaneous O2-production step by thermally-activated chemical regeneration with regenerated charge density of 9.63 C cm−2 and electricity saving of 18.2 % in a membrane-free cell. The as-proposed system enables low-grade heat to facilitate the overall performance of water electrolysis, which potentially paves the way for multi-energy coupling for H2-production.