Surface reconstruction of Se-doped NiS₂ enables high-efficiency oxygen evolution reaction

Surface reconstruction of electrocatalysts has been widely witnessed during the electrochemical processes. Here, NiS₂, NiSe₂, and Se doped NiS₂ (Se-NiS₂) are fabricated for oxygen evolution reaction (OER) through a mild sulfuration and/or selenylation process of Ni(OH)₂ supported on carbon cloth (CC). Through careful in-situ Raman spectroscopy and ex-situ X-ray photoelectron spectroscopy, surface reconstruction of NiS₂, NiSe₂, and Se-NiS₂ during the OER process has been revealed. A potential-dependent study shows that Se-NiS₂ undergoes surface evolution at lower potentials and requires the lowest potential for conversion to NiOOH as a highly OER-active species, accompanied by the leaching of SO₄²⁻ and SeO₄²⁻ that can again be adsorbed on the catalyst surface to enhance the catalytic activity. Density functional theory (DFT) calculations confirm that Se-NiS₂ is more susceptible to surface oxidation through the OER process. Therefore, Se-NiS₂ exhibits outstanding OER activity and stability in alkaline conditions, requiring an overpotential of 343 mV at a current density of 50 mA cm⁻². A novel insight is provided by our work in understanding the surface reconstruction and electrocatalytic mechanism of Ni-based chalcogenides.