Nitrogen Doping in NiS/Ni3S4 Nanowire-Based Electrocatalysts for Promoting the Second-Order Hydrogen Evolution Reaction

In electrochemistry, predicting the mechanistic pathway for the hydrogen evolution reaction (HER) can be challenging, as it is constantly altered by the electronic and geometrical structures of the surface of the electrocatalyst. However, through a combined experimental and theoretical approach, we have successfully demonstrated the functions of nitrogen (N) dopants in NiS/Ni3S4 catalysts. Here, we have developed a cost-effective, environmentally friendly, and highly efficient electrochemical HER catalyst using a N-doped NiS/Ni3S4 nanowire via a hydrothermal approach and calcination method to incorporate different concentrations (1, 3, 6, 8, and 10%) of nitrogen. These electrocatalysts were synthesized to efficiently produce hydrogen from water. Interestingly, the 6% nitrogen-doped NiS/Ni3S4 nanowire electrocatalyst exhibited superior catalytic HER. The inclusion of N dopants has distinct functions, including the activation of the HER catalytic activity of NiS/Ni3S4 by augmenting the number of active sites on its surface. This enables second-order H2 production, which has been shown through extensive electrochemical analyses. The active sites for the HER in N-doped NiS/Ni3S4 nanowires have been identified using density functional theory-based calculations, which reveal that the strong hybridizations of 3d orbitals of Ni and 2p of S and N near the Fermi level result in the distribution of conduction charges across the N-doped surface. Our experimental and theoretical combined investigation indicates that the superior HER activity of N-doped NiS/Ni3S4 nanowires is promising for the sustainable production of hydrogen using electrolysis of water.