Lattice Engineering Triggered Phase Formation of Bimetallic Thiospinels with Excellent HzOR and OER Activity for Energy‐Efficient Hydrogen Production

Abstract Introducing foreign elements into a crystal lattice could trigger phase transformation, serving as an excellent means to fabricate highly electrocatalytic phases. NiCo 2 S 4 is a notably electrocatalytic thiospinel phase, normally synthesized via a two‐step route and rarely explored for electrocatalytic hydrazine oxidation reaction (HzOR). This work reports one‐step hydrothermal synthesis of NiCo 2 S 4 and CuCo 2 S 4 and their performance for HzOR and oxygen evolution reaction (OER). Time dependent syntheses suggest formation of (M, Co) 9 S 8 ; M═Ni/Cu phase, followed by conversion to the respective thiospinel phase. Computational study validates that the incorporation of Ni into Co 9 S 8 disrupts its stability and induces the formation of a stable bimetallic thiospinel phase. Even without the assistance of metal foam substrate, NiCo 2 S 4 displayed remarkable activity for HzOR requiring potentials of 153 and 350 mV to afford current densities of 10 and 500 mA/cm 2 , respectively. Furthermore, NiCo 2 S 4 showed good activity for OER, providing 10 mA/cm 2 at 290 mV. For hydrazine‐assisted H 2 production, the two‐electrode setup, NiCo 2 S 4 ||Pt/C attained a current density of 10 mA/cm 2 at 140 mV, which is 1.39 V less than that required for conventional water electrolyzer (1.53 V). Long‐term durability of NiCo 2 S 4 for both HzOR and OER at high current densities highlights the suitability of the catalyst for practical applications.