Single-Step Electrodeposited Molybdenum Incorporated Nickel Sulfide Thin Films from Low-Cost Precursors as Highly Efficient Hydrogen Evolution Electrocatalysts in Acid Medium

Large-scale production of hydrogen-the energy carrier of the future remains challenging on economy grounds. Low-cost synthetic designs are necessary to produce electrocatalysts for hydrogen evolution reaction (HER). Ternary nickel molybdenum sulfides Ni1-xMoxS (x = 0, 0.04, 0.08, 0.16) have been electrochemically grown on fluorine- doped tin oxide substrate as highly active and stable HER electrocatalysts. The merits of this method are (1) the electrochemical method is energy efficient at ambient conditions and can be easily scaled up on large surface area substrates; (2) Ni, Mo, and S precursors used for the deposition are readily available and relatively cheaper compared to similar methods; and (3) the synthesis procedure is simple, one step, and requires no further heat treatments. The deposited thin films have been examined using regular physical characterization techniques, and their HER activity has been evaluated through electrochemical methods. Ni0.96Mo0.04S, especially, has exhibited a promising HER activity with a lowest Tafel slope of 46 mV/dec. The mechanistic aspects of HER on the thin films have been extensively studied by voltammetric and impedance methods. Tafel analysis and double-layer capacitance measurements have revealed that the high activity of Ni0.96Mo0.04S can be attributed to the larger electrochemical surface area and the faster discharge of protons in the initial Volmer step. Moreover, stability tests performed on various thin films have shown that Mo-doped thin films could retain more than 80% of the initial activity whereas NiS has lost more than 50% of the same.