COBALT BLACK ELECTRODES FOR THE OXYGEN EVOLUTION REACTION FROM ELECTROLYSIS OF 40 WT-PERCENT KOH

The oxygen evolution reaction (OER) has been investigated on cobalt black electrodes in 40 wt% KOH solution at temperatures ranging from 40 to 80-degrees-C. The electrocoatings were obtained from a bath containing dissolved ammonium citrate and cobalt sulphate at pH 9.8 and 23-degrees-C. The charge related to the reduction of oxide(s)/hydroxide(s) (Q(RED)) after preanodization under a current density of 1 A cm-2 at 70-degrees-C increases linearly with the cobalt deposition time. The larger the Q(RED), the better the electrocatalytic activity. For current densities ranging from 10(-4) to 1 A cm-2, log i vs overpotential potential diagrams display a single Tafel region at 40 and 50-degrees-C, compared to two regions at 60, 70 and 80-degrees-C. The high value of the apparent energy of activation in the regions of high overpotentials, i.e. 120 kl mol - 1, means that electrocatalytic activity largely improved from 40 to 80-degrees-C.