Nanostructured Ni–Co alloy electrodes for both hydrogen and oxygen evolution reaction in alkaline electrolyzer

Abstract

Ni–Co alloy nanostructured electrodes with high surface area were investigated both as a cathode and anode for an alkaline electrolyzer. Electrodes were obtained by template electrosynthesis at room temperature. The electrolyte composition was tuned in order to obtain different NiCo alloys. The chemical and morphological features of nanostructured electrodes were evaluated by EDS, XRD and SEM analyses. Results show that electrodes with different composition of Ni and Co, made of nanowires well anchored to the substrate, were obtained. For both hydrogen and oxygen evolution reactions, electrochemical and electrocatalytic tests, performed in 30% w/w KOH aqueous solution, were carried out to establishing the best alloy composition. Mid-term tests conducted at a constant current density were also reported. Nanostructured electrodes with a Co atomic composition of 94.73% have the best performances for both hydrogen and oxygen evolution reactions. In particular, with this alloy, a potential of −0.43 V (RHE) and of 1.615 V (RHE) was measured for hydrogen and oxygen evolution reaction at −50 mA cm−2 and at 50 mA cm−2, respectively, after 6 h of electrolysis. The calculated Tafel's slopes for HER and OER were −0.105 and 0.088 V/dec, respectively. Furthermore, HER and OER η10 potential values were measured founding −0.231 V (RHE) and 1.494 V (RHE) respectively.