Electrodeposition of Co–Pd alloys from ammonia solutions and their catalytic activity for hydrogen evolution reaction

Abstract

Investigations of the influence of electrolysis parameters such as the concentration of metal ammonia complexes, working electrode potential and temperature on the composition, structure and catalytic activity of synthesized alloys for water molecule reduction reaction in 2 M NaOH (T = 25 °C) were conducted. The alloys were deposited under potentiostatic conditions within potential range from −0.7 to −1.1 V in electrolytes of pH 9.5, containing ammonia complexes of cobalt(III) and palladium(II), [Co(NH3)6]3+ and [Pd(NH3)4]2+, of different concentration ratio. Structural changes in electrodeposited alloys were discussed based on results of X-ray diffraction measurements. An elemental analysis was performed using the energy-dispersive X-ray spectroscopy technique. Finally, based on results of galvanostatic measurements, the Tafel slope within the range of activation control for hydrogen evolution reaction was determined and mechanism of the process was discussed. The alloys presented low Tafel slope value, from 25.4 to 88.7 mV dec−1. The alloy of the highest activity for hydrogen evolution reaction contained 31.2 at.% of Pd.