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 (H and O ) 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@Ni Co -P) material as a tri-functional (redox mediator, hydrogen evolution reaction (HER), oxygen evolution reaction (OER)) electrode. The versatile GF@Ni Co -P electrode obtained by a one-step electrodeposition not only exhibits high specific capacity (176 mAh g at 0.5 A g ) 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@Ni Co -P electrode endow this decoupled system with more flexibility for H production by fluctuating renewable energies. This work provides guidance for multifunctional applications of transition metal compounds between energy storage and electrocatalysis.