Cobalt-based Co 3 Mo 3 N/Co 4 N/Co Metallic Heterostructure as a Highly Active Electrocatalyst for Alkaline Overall Water Splitting.

Alkaline water electrolysis holds promise for large-scale hydrogen production, yet it encounters challenges like high voltage and limited stability at higher current densities, primarily due to inefficient electron transport kinetics. Herein, a novel cobalt-based metallic heterostructure (Co 3 Mo 3 N/Co 4 N/Co) is designed for excellent water electrolysis. In operando Raman experiments reveal that the formation of the Co 3 Mo 3 N/Co 4 N heterointerface boosts the free water adsorption and dissociation, increasing the available protons for subsequent hydrogen production. Furthermore, the altered electronic structure of the Co 3 Mo 3 N/Co 4 N heterointerface optimizes ΔG H of the nitrogen atoms at the interface. This synergistic effect between interfacial nitrogen atoms and metal phase cobalt creates highly efficient active sites for the hydrogen evolution reaction (HER), thereby enhancing the overall HER performance. Additionally, the heterostructure exhibits a rapid OH - adsorption rate, coupled with great adsorption strength, leading to improved oxygen evolution reaction (OER) performance. Crucially, the metallic heterojunction accelerates electron transport, expediting the afore-mentioned reaction steps and enhancing water splitting efficiency. The Co 3 Mo 3 N/Co 4 N/Co electrocatalyst in the water electrolyzer delivers excellent performance, with a low 1.58 V cell voltage at 10 mA cm -2 , and maintains 100 % retention over 100 hours at 200 mA cm -2 , surpassing the Pt/C||RuO 2 electrolyzer.