Effectiveness of sodium citrate on electrodeposition process of NiCoW alloys for hydrogen evolution reaction

In this study NiCoW alloys have been produced by electrodeposition on Al net. Two electrolytic baths, with and without sodium citrate, having the same metal ion content (20 g/l Ni, 8 g/l Co and W in the range 2-8 g/l) and boric acid content 20 g/l, have been used. Temperature and current density operative conditions have been varied in the range 30-60 °C and 260-350 A/m2 respectively. The electrodeposition performed in the presence of sodium citrate presents always the best results in term of current efficiency and specific energy consumption, while W content in the alloy highlights different behavior: W content increasing with temperature by using citrate in solution and quite constant W content with temperature, without citrate. Morphological and structural analyses of deposits have been also performed to assess the electrolysis conditions and to obtain the best deposit. Preliminary electrochemical tests have been also carried out on NiCoW deposits for establishing their ability to act as cathode for HER and to compare these ternary alloys with NiCo binary alloys, thus detecting W positive influence in both hydrogen overvoltage and exchange current density. The W presence in the alloys affects, in the same way, the HER independently of the used bath for their production.