TRANSITION METAL-BASED CATHODES FOR HYDROGEN EVOLUTION IN ALKALINE-SOLUTION - ELECTROCATALYSIS ON NICKEL-BASED TERNARY ELECTROLYTIC CODEPOSITS

Nickel-molybdenum-iron, nickel-molybdenum-copper, nickel-molybdenum-zinc, nickel-molybdenum-cobalt, nickel-molybdenum-tungsten and nickel-molybdenum-chromium ternary codeposits, obtained through electrodeposition on mild steel strips have been characterized with the objective of qualitatively comparing and assessing their electrocatalytic activities as hydrogen electrodes in alkaline solution. It has been concluded that their electrocatalytic effects for the hydrogen evolution reaction (h.e.r.) rank in the following order: Ni-Mo-Fe > Ni-Mo-Cu > Ni-Mo-Zn > Ni-Mo-Co approximately Ni-Mo-W > Ni-Mo-Cr > Ni-plated steel. Further investigations on these electrocatalysts have revealed that the cathodic overpotential contribution to the electrolysis voltage can be brought down by 0.3 V when compared with conventional steel cathodes. The best and most stable hydrogen evolving cathode of these, namely Ni-Mo-Fe, exhibited an overpotential of about 0. 187 V for over 1500 h of continuous electrolysis in 6 M KOH at 300 mA cm-2 and 353 K. The salient features of the codeposits, such as physical characteristics, chemical composition, current-potential behaviour and the varying effects of the catalytic activation method were analysed with a view to correlating the micro-structural characteristics of the coatings with the hydrogen adsorption process. The stability under open circuit conditions, the tolerance to electrochemical corrosion and the long term stability of Ni-Mo-Fe codeposit cathodes were very encouraging. An attempt to identify the pathway for the h.e.r. on these codeposit cathodes was made, in view of the electrochemical parameters obtained experimentally.