Plasma Engineering of Basal Sulfur Sites on MoS₂@Ni₃S₂ Nanorods for the Alkaline Hydrogen Evolution Reaction

Inexpensive and efficient catalysts are crucial to industrial adoption of the electrochemical hydrogen evolution reaction (HER) to produce hydrogen. Although two-dimensional (2D) MoS₂ materials have large specific surface areas, the catalytic efficiency is normally low. In this work, Ag and other dopants are plasma-implanted into MoS₂ to tailor the surface and interface to enhance the HER activity. The HER activty increases initially and then decreases with increasing dopant concentrations and implantation of Ag is observed to produce better results than Ti, Zr, Cr, N, and C. At a current density of 400 mA cm⁻², the overpotential of Ag500-MoS₂@Ni₃S₂/NF is 150 mV and the Tafel slope is 41.7 mV dec⁻¹. First-principles calculation and experimental results reveal that Ag has higher hydrogen adsorption activity than the other dopants and the recovered S sites on the basal plane caused by plasma doping facilitate water splitting. In the two-electrode overall water splitting system with Ag500-MoS₂@Ni₃S₂/NF, a small cell voltage of 1.47 V yields 10 mA cm⁻² and very little degradation is observed after operation for 70 hours. The results reveal a flexible and controllable strategy to optimize the surface and interface of MoS₂ boding well for hydrogen production by commercial water splitting.