Electrocatalytic oxygen evolution on nickel oxy-hydroxide anodes: Improvement through rejuvenation

The ageing and rejuvenation behaviour of nickel oxy-hydroxide anodes for alkaline water electrolysis is investigated. The anodically formed oxy-hydroxide material is known to age over time causing a decrease in performance. However, this deactivation can be mitigated by temporarily reducing the potential for brief periods. This work looks at continuous rejuvenation of nickel anodes in 30 wt.% KOH solution and it is shown that rejuvenation at 0.5 V vs. HgHgO for 10 minutes every 100 minutes can prevent ageing of the anode, thus maintaining a low overpotential during galvanostatic oxygen evolution at 50 mA cm−2. It is suggested that the short potentiostatic rejuvenation periods at regular intervals prevents the ratio of Ni(IV) to Ni(III) from increasing, thereby maintaining the intrinsic activity of the material. The rejuvenation potential must be above 0.36 V vs. HgHgO to ensure it is effective in obtaining good performance (i.e. the material must not reduce to Ni(II)). These findings suggest that electrolysis systems using nickel anodes could benefit from direct coupling to fluctuating power sources such as solar or wind, where the variability in their power output could facilitate the rejuvenation of the nickel anode. We estimate that by using the rejuvenation steps, an energy saving of 9% is possible in an alkaline water electrolyser using nickel anodes.