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

Abstract

The weak orbital coupling between Ni₃N and H₂O, caused by its interstitial structure and attenuated Ni–N interaction, is attributed to the high unoccupied d orbital energy of Ni₃N. 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 Ni₃N, which resulted in an exceptionally efficient HER. The as-synthesized Ni₃N catalyst demonstrates an overpotential of 135 mV when subjected to a current density of 10 mA cm⁻². 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 Ni₃N 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.