Effect of deposition conditions on the properties of Ni–Mo–W coatings as electrocatalysts for hydrogen evolution reaction

Ni–Mo–W electrocatalysts have been prepared by electrodeposition on a copper substrate in a bath with different Na2WO4·2H2O concentrations (0.01–0.1 M) and pH values (4 and 7.5). The chemical composition, surface morphology, and crystalline structure of the as-prepared electrocatalysts were followed by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) techniques. The chronopotentiometry and electrochemical impedance spectroscopy (EIS) methods were conjointly used to investigate the Ni–Mo–W electrocatalysts’ activity for hydrogen evolution reaction (HER) in alkaline medium. As estimated by EDX results, Ni is the major element in all the synthesized Ni–Mo–W deposits, and Mo and W contents are pH and Na2WO4·2H2O concentrations dependent. The XRD results reveal the formation of a nanocrystalline FCC-Ni(Mo, W) solid solution at pH 4, while at pH 7.5, the deposits present an amorphous structure. The deposits prepared at pH 4 have homogeneous surface with a needle-like morphology but at pH 7.5, a cracked morphology with a uniform and regular porous structure is observed. According to the electrochemical analyses, the Ni–Mo–W electrocatalyst developed at pH 7.5 and [WO42−] = 0.01 M with maximum Mo and minimum W contents was found to be the best electrode material for HER in alkaline media. This electrocatalyst exhibits low overpotential, η, and charge-transfer resistance, Rct, values associated to higher values for the double-layer capacitance, Cdl, and the roughness factor, Rf.