Electrochemical and morphological studies of electrodeposited Ni–Fe–Mo–Zn alloys tailored for water electrolysis

The co-deposition of nickel, iron and molybdenum onto mild steel substrates with or without the addition and subsequent leaching of zinc rendered cathode materials very active for hydrogen generation in alkaline solutions. SEM analysis showed that adherence to the substrate can be achieved by initial deposition of the other components prior to Zn incorporation into the solution. Coatings of Ni–Fe–Mo (51.4-5.5-43.1 at%) and Ni–Fe–Mo–(Zn) (70.9-15.3-12.7-1.1 at% after leaching) were very active for hydrogen evolution at temperatures ranging from 25 to 80°C in 6 M KOH solutions. Steady-state polarisation curves furnished Tafel plots with slopes almost invariant with temperature and revealed an electrochemical activity comparable to the best materials reported so far. For the Ni–Fe–Mo–(Zn) coating the overpotential for hydrogen evolution at 80°C was as low as 83.1 mV. Long-time electrolyses at a constant current density of 135 mA cm−2 showed a considerable degradation of the surface and a decay in performance but the overpotential value after 440 h stabilised in 157 mV, a satisfactory value for industrial applications.