A phase-engineered nickel sulfide and phosphide (NiS–Ni2P) heterostructure for enhanced hydrogen evolution performance supported with DFT analysis

Abstract

The search for an earth-abundant, efficient, and durable electrocatalyst via a one-step hydrothermal approach is more favorable for the generation of green energy carriers such as hydrogen (H₂) through a simple electrolysis process. This report considers a hydrothermal synthesis of a phase-engineered nickel sulfide and nickel phosphide (NiS–Ni₂P) heterostructure having organized quasi-spherical morphology of nickel sulfide (NiS) nanoparticles and rod-like morphology of nickel phosphide (Ni₂P). The enhancement of the hydrogen evolution reaction (HER) performance could be attributed to the formation of a heterostructure interface between the two phases. The prepared NiS–Ni₂P electrode material needed 147 mV of overpotential to reach 10 mA cm⁻² of cathodic current density and a Tafel slope of 68 mV dec⁻¹ follows the Volmer–Heyrovsky reaction path to execute the HER. The theoretical studies further support the observed experimental results, whereas we have investigated the structural and electronic properties of nickel sulfide (NiS), nickel phosphide (Ni₂P), and the hybrid NiS–Ni₂P structure by employing state-of-the-art density functional theory (DFT) simulation to find their HER activities. In the (NiS–Ni₂P) heterostructure, there is charge transfer from Ni₂P to NiS which may increase the conductivity as well as catalytic activity towards the HER for hybrid NiS–Ni₂P. The computed overpotential follows the trend NiS > Ni₂P > hybrid NiS–Ni₂P, matching closely with the experimental data. The above experimental and theoretical studies give an idea of synthesizing a phase-engineered, morphology-tuned NiS–Ni₂P heterostructure as a noble metal-free electrocatalyst for the generation of green energy fuels such as hydrogen (H₂).