A hydrophilic Ni ₃ S ₂ –MoN heterostructure on Ni foam (Ni ₃ S ₂ –MoN/NF) as an electrocatalyst for enhanced hydrogen evolution in alkaline media

In this study, a Ni₃S₂-MoN heterostructure was directly synthesized on a Ni foam support (Ni₃S₂-MoN/NF) through a facile one-step annealing process, using MoCl₅ and thiourea at 450 °C under an N₂ gas flow. The synthesized Ni₃S₂-MoN/NF catalyst achieved exceptional hydrogen evolution reaction (HER) activity, with low overpotential values of 154.3 mV (η₅₀) at 50 mA cm^-2 and 186.3 mV (η₁₀₀) at 100 mA cm^-2 in 1.0 M KOH. The enhanced HER performance was attributed to the synergistic effect between the highly active Ni₃S₂-MoN heterostructure and the NF support, which offers a large surface area and excellent electrical conductivity. Density functional theory (DFT) calculations reveal that MoN strongly adsorbs H₂O and OH, facilitating water dissociation. Additionally, MoN was found to induce structural modifications in Ni₃S₂, enhancing the hydrogen binding energy and thereby improving the HER activity. Furthermore, the inherently hydrophobic Ni₃S₂ surface was transformed into a hydrophilic Ni₃S₂-MoN surface, further enhancing the HER activity. In a 24 h stability test at 100 mA cm^-2, the HER activity of Ni₃S₂-MoN/NF improved, due to the partial conversion of Ni₃S₂ into amorphous Ni(OH)₂ species, resulting in a reduction of overpotential by 30 mV (η₅₀ = 125.5 and η₁₀₀ = 158.2 mV). This simple and economical synthesis method highlights the potential of Ni₃S₂-MoN/NF as a promising catalyst for the HER with high activity and stability.