Amorphous-Ni(OH)₂ on a Vertically Grown Lamellar Ag-Modified MoSx Thin-Film Electrode with Surface Defects for Hydrogen Production in Alkaline Solutions

A low-temperature radio-frequency-sputtered Ag-modified MoS x lamellar thin-film electrode with a home-made target was deposited on a carbon-cloth substrate and electrochemically modified with amorphous Ni(OH) 2 . All the as-prepared thin-films’ properties were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. Electrochemical measurements of a-Ni(OH) 2 /Ag-modified MoS x lamellar thin films exhibited promising hydrogen evolution reaction properties in alkaline solutions. The linear sweep voltammetry and electrochemical impedance spectroscopy measurements indicated a relatively low Tafel slope of 95.3 mV/dec and a low electron-transfer resistivity of 12.26 Ω, respectively. The observed overpotentials were 0.12 and 0.26 V at 10 and 100 mA, respectively. Furthermore, cyclic voltammetry measurements revealed that the thin-film electrode had the highest double-layer capacity ( C dl ) of 11.3 mF/cm 2, which also implied a highly active electrochemical surface area. Finally, the stability of a-Ni(OH) 2 /Ag-modified MoS x thin films was examined with a constant current density of 10 mA/cm 2 for 20 h. It was found that the non-stoichiometric MoS x played an essential role in the water-activation process due to the presence of sulfur-vacancy sites (V S 2+ ). During the electrochemical process, V S 2+ acts as an active site to pin water and weaken the OH–H bonding, in which the water-originated OH is further bonded with periodically terminated surface defect of Ni(OH) x on the electrode. The defected Ni(OH) x on the catalyst surface helps the dissociation of OH bonding in water adsorbed on Ag-MoS x to generate H* intermediates for further Heyrovsky steps. The low-cost thin-film electrode with a relatively low overpotential is promising for industrial applications based on the experimental data.