Enhancing hydrogen evolution by heterointerface engineering of Ni/MoN catalysts

• A programmed nitridation protocol is used to create Ni/MoN heterointerface. • In situ phase separation induces electronic interaction between Ni and Mo atoms. • Electron transfer from MoN to metallic Ni to generate a built-in electric field. • The catalyst needs an overpotential of 95 mV for a current density of 10 mA cm −2. • The catalyst shows no morphology or composition changes at 100 mA cm −2 for 100 h. Molybdenum nitrides have garnered significant attention for their potential in the hydrogen evolution reaction (HER) due to their metallic behavior, abundant reserves, and pH-universal stability. However, their unsatisfactory hydrogen adsorption limits industrial applications. Heterostructures can be designed to introduce defects and modulate the electronic structure of catalysts to optimize hydrogen adsorption to enhance HER. Nevertheless, the exact active sites at the heterointerface and the fundamental mechanisms underlying the HER process remain inadequately understood. Herein, a composite electrocatalyst in which metallic Ni and MoN phases (Ni/MoN) form the heterointerface between them is fabricated. The heterointerface produces strong electronic interactions between Ni and MoN to facilitate electron transfer from MoN to Ni, and the built-in electric field facilitates charge transfer during electrocatalysis. This optimized electronic configuration with abundant active sites delivers excellent performance in alkaline HER. Density-functional theory calculations demonstrate that H 2 O dissociates at the Ni site, whereas H 2 desorption occurs at the Mo site. As a result, Ni/MoN/CC requires an overpotential of only 95 mV to achieve a current density of 10 mA cm −2 and a Tafel slope of 104 mV dec −1 . Moreover, it maintains a high current density of 100 mA cm −2 for 100 h with negligible morphological or compositional changes. The strategy of modulating the electronic structure of low-cost, transition metal-based heterostructured electrocatalysts is an effective and commercially viable means to design and develop high-performance electrocatalysts for water splitting.