Surface structure evolution of bimetallic nickel tungsten nitride (Ni2W3N) for high performance hydrogen evolution†

Bimetallic transition metal nitride (TMN)-based electrocatalysts have demonstrated potential for the hydrogen evolution reaction (HER) in alkaline electrolytes. However, achieving simpler synthesis methods and a deeper understanding of their catalytic activity remains challenging. Here, we report a facile synthesis strategy for Ni₂W₃N directly on nickel foam (Ni₂W₃N/NF). Unlike conventional methods for synthesizing bimetallic TMN-based catalysts requiring two-step annealing, our approach streamlines the annealing process into a one-step. It also eliminates the use of toxic NH₃ gas and additional Ni precursors. Notably, this work is the first to report Ni₂W₃N/NF as an HER catalyst. The resulting Ni₂W₃N/NF exhibits one of the best HER performances among bimetallic TMN-based catalysts, with low overpotential values of 46.5 and 78.7 mV at current densities of 50 and 100 mA cm⁻², respectively, and demonstrates high stability for 72 h. In situ Raman spectroscopy reveals surface reconstruction during the HER process, characterized by tungsten dissolution and the formation of amorphous Ni(OH)₂. Density functional theory calculations indicate that the Ni sites in amorphous Ni(OH)₂ serve as active sites, enhancing water dissociation and optimizing hydrogen binding energy. This facilitates an efficient Volmer reaction, thereby improving HER performance.