Electrodeposition and characterization of NiMoW alloy as electrode material for hydrogen evolution in alkaline water electrolysis

The electrodeposition of ternary NiWMo alloys films from citrate ammonia-free electrolyte at room temperature was studied in an effort to evaluate the effect of applied potential on the composition limits, corrosion resistance and the electrocatalytic properties of the deposits towards the hydrogen evolution reaction (HER) in concentrated alkaline solution. The alloys were potentiostatically electrodeposited onto pure copper sheet substrates. The electrodeposits were characterized by means of field-emission scanning microscopy (FESEM) and energy dispersive X-ray analysis (EDXA). In an electrolyte where MoO42−/WO42−=1:1, at a given deposition potential, there is more Mo than W in the deposits, indicating an advantageous induced co-deposition of Mo compared to W. The nucleation mechanism, studied according to Scharifker-Hills theoretical model, revealed an instantaneous nucleation followed by a three-dimensional growth. On the hand, increasing MoO42−/WO42− ratio in the electrolyte under the same deposition potential reduced both Ni and W content in the deposits. A different trend was observed in an equimolar solution, when applying more negative potentials, both Mo and W contents decreased leading to the enhancement of Ni amount. The stability in corrosive media and the catalytic performances of the coatings depended mainly on the applied overpotentials, A mechanism of induced co-deposition of molybdenum and tungsten with nickel is proposed and discussed.