Heterophase junction engineering-induced Co spin-state modulation of CoSe₂ for large-current hydrogen evolution reaction

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 CoSe₂ electrocatalysts. The composition of the electrocatalysts consisting of both cubic CoSe₂ (c-CoSe₂) and orthorhombic CoSe₂ (o-CoSe₂) 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 CoSe₂-based heterophase catalyst with the optimal c-CoSe₂ 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.