A computational investigation on transition metal substituted two-dimensional pentagonal nickel diazenide (NiN2) for the hydrogen evolution reaction via water splitting

Abstract

Two-dimensional pentagonal nickel diazenide (NiN₂) has drawn significant attention as a promising electrocatalyst for the hydrogen evolution reaction (HER), owing to its unique structural and electronic properties. Density functional theory calculations were employed to explore the catalytic enhancement of NiN₂ through transition metal (Co, Cr, Fe, Mo, V, Pd, Pt, and W) substitutions. The substitution of TM atoms drastically alters the electronic structure, effectively optimizing the hydrogen adsorption properties by fine-tuning the Gibbs free energy of hydrogen adsorption (ΔG_H*). Among the studied candidates, Mo-substituted NiN₂ emerged as the most efficient, with a nearly ideal Gibbs free energy, low overpotential (η) of 87 meV and an enhanced density of states near the Fermi level. Moreover, the substitution of the TM alters the bandgap and transforms the penta-Nickel Diazenide (p-NiN₂) into a semiconducting system. At room temperature, total potential energy and bond distance remain stable as a function of time, with no significant geometrical structure distortion observed in ab initio molecular dynamics (AIMD) simulations. Additionally, an activation barrier of 1.33 eV for the Tafel reaction has been determined using climbing image nudged elastic band (CI-NEB) calculations, underscoring the advantageous kinetics of Mo–NiN₂ for hydrogen evolution. These findings underscore the potential of TM-substituted NiN₂, particularly Mo-doped systems, as highly effective catalysts for the HER, paving the way for innovative advancements in water-splitting and next-generation sustainable energy technologies.