Selenium-Enriched Nickel Selenide Nanosheets as a Robust Electrocatalyst for Hydrogen Generation

To address the urgent need for clean and sustainable energy, the rapid development of hydrogen-based technologies has started to revolutionize the use of earth-abundant noble-metal-free catalysts for the hydrogen evolution reaction (HER). Like the active sites of hydrogenases, the cation sites of pyrite-type transition-metal dichalcogenides have been suggested to be active in the HER. Herein, we synthesized electrodes based on a Se-enriched NiSe₂nanosheet array and explored the relationship between the anion sites and the improved hydrogen evolution activity through theoretical and experimental studies. The free energy for atomic hydrogen adsorption is much lower on the Se sites (0.13 eV) than on the Ni sites (0.87 eV). Notably, this electrode benefits from remarkable kinetic properties, with a small overpotential of 117 mV at 10 mA cm^-2, a low Tafel slope of 32 mV per decade, and excellent stability. Control experiments showed that the efficient conversion of H⁺into H₂is due to the presence of an excess of selenium in the NiSe₂nanosheet surface. Excess selenium: Although the undercoordinated surface metal centers of pyrite-type transition-metal dichalcogenides have been suggested to be the main active sites for H₂production, the ligand composition also plays a decisive role. The Se sites and excessive Se atoms on the surface of pyrite-type NiSe₂are now corroborated to be the active sites for electrochemical H₂evolution.