Enhancing the electronic structure of Ni-based electrocatalysts through N element substitution for the hydrogen evolution reaction.

The weak orbital coupling between NiN and HO, caused by its interstitial structure and attenuated Ni-N interaction, is attributed to the high unoccupied d orbital energy of NiN. Consequently, the kinetics for water dissociation in the HER are slow. In this study, we effectively lowered the energy state of vacant d orbitals in NiN, which resulted in an exceptionally efficient HER. The as-synthesized NiN catalyst demonstrates an overpotential of 135 mV when subjected to a current density of 10 mA cm. The refined structural characterization suggests that the introduction of oxygen results in a reduction in electron densities surrounding the Ni sites. Furthermore, DFT calculations provide additional evidence that the electrocatalyst of NiN generates a greater number of lowest unoccupied orbitals (LUMOs) and improved alignment, thereby enhancing the adsorption and splitting of water. The notion of orbital-regulated electronic levels on Ni sites introduces a distinctive methodology for the systematic development of catalysts used in hydrogen evolution and other applications.