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.