Heterophase junction engineering‐induced Co spin‐state modulation of CoSe ₂ for large‐current hydrogen evolution reaction

Abstract Efficient electrocatalysts are vital to large‐current hydrogen production in commercial water splitting for green energy generation. Herein, a novel heterophase engineering strategy is described to produce polymorphic CoSe 2 electrocatalysts. The composition of the electrocatalysts consisting of both cubic CoSe 2 (c‐CoSe 2 ) and orthorhombic CoSe 2 (o‐CoSe 2 ) phases can be controlled precisely. Our results demonstrate that junction‐induced spin‐state modulation of Co atoms enhances the adsorption of intermediates and accelerates charge transfer resulting in superior large‐current hydrogen evolution reaction (HER) properties. Specifically, the CoSe 2 ‐based heterophase catalyst with the optimal c‐CoSe 2 content requires an overpotential of merely 240 mV to achieve 1,000 mA·cm −2 as well as a Tafel slope of 50.4 mV·dec −1 . Furthermore, the electrocatalyst can maintain a large current density of 1,500 mA·cm −2 for over 320 h without decay. The results reveal the advantages and potential of heterophase junction engineering pertaining to design and fabrication of low‐cost transition metal catalysts for large‐current water splitting.