A Membrane-Free Decoupled Water Electrolyzer Operating at Simulated Fluctuating Renewables with Tri-Functional NiCo-P Electrode

Water electrolysis has been considered a promising technology for the conversion of renewables to hydrogen. However, preventing mixing of products (H2 and O2) and exploring cost-efficient electrolysis components remains challenging for conventional water electrolyzers. Herein, we designed a membrane-free decoupled water electrolysis system by using graphite felt supported nickel-cobalt phosphate (GF@NixCoy-P) material as a tri-functional (redox mediator, hydrogen evolution reaction (HER), oxygen evolution reaction (OER)) electrode. The versatile GF@Ni1Co1-P electrode obtained by a one-step electrodeposition not only exhibits high specific capacity (176 mAh g−1 at 0.5 A g−1) and long cycle life (80 % capacity retention after 3000 cycles) as a redox mediator, but also has relatively outstanding catalytic activities for HER and OER. The excellent properties of the GF@NixCoy-P electrode endow this decoupled system with more flexibility for H2 production by fluctuating renewable energies. This work provides guidance for multifunctional applications of transition metal compounds between energy storage and electrocatalysis.