Sulfur-Doped CoSe₂ Porous Nanosheets as Efficient Electrocatalysts for the Hydrogen Evolution Reaction

The electrochemical hydrogen evolution reaction (HER), as a promising route for hydrogen production, demands efficient and robust noble-metal-free catalysts. Doping foreign atoms into an efficient catalyst such as CoSe 2 could further enhance its activity toward the HER. Herein, we developed a solvothermal ion exchange approach to doping S into CoSe 2 nanosheets (NSs). We provide a combined experimental and theoretical investigation to establish the obtained S-doped CoSe 2 (S-CoSe 2 ) nanoporous NSs as highly efficient and Earth-abundant catalysts for the HER. The optimal S-CoSe 2 catalyst delivers a catalytic current density of 10 mA·cm –2 for the HER at an overpotential of only 88 mV, demonstrating that S-CoSe 2 is one of the most efficient CoSe- and CoS-based catalysts for the HER. We performed density functional theory (DFT) calculations to determine the stable structural configurations of S-CoSe 2, and on the basis of which, we calculated the hydrogen adsorption Gibbs free energy (Δ G H ) on CoSe 2, CoS 2, and the S-CoSe 2 and the barrier energies of the rate-determining step of the HER on S-CoSe 2 . DFT calculations reveal that S-doping not only decreases the absolute value of Δ G H (move toward zero) but also significantly lowers the kinetic barrier energy of the rate-determining step of the HER on S-CoSe 2, leading to a greatly improved HER performance.