Boosting Alkaline Water Oxidation: The Power of Electrolyte Design on Ni Thin Films

Abstract Anion exchange membrane water electrolysis and alkaline water electrolysis (AWE) hold the potential to become a viable energy vector in the future as the world moves away from fossil fuels. However, the sluggish oxygen evolution reaction (OER) impedes the efficiency of these techniques, and the cost of producing hydrogen via electrolysis is still significantly higher than that of natural gas reforming. Nickel is widely the most used anode material for the OER, since the Fe impurities naturally present in the electrolyte greatly boost the performance of these Ni-based anodes. In this work, the effect of other spiked metal impurities on the OER performance of a Ni thin film was systematically studied. Results show a clear increase performance upon the addition of Fe2+, Fe3+, and Co2+ to the electrolyte. More specifically, at 1.75 VRHE, an increase in turnover frequencies (TOF) of 0.45, 0.61, and 0.14 1/s for Fe2+, Fe3+, and Co2+, respectively, was measured relative to unpurified KOH. Additionally, relative to unpurified KOH, overpotential drops of 92, 113, and 10 mV at 0.1 mA/cm2EASA, respectively, was measured. Next, a significant change in Tafel slope for these impurities was observed, leading to a significant change in rate-determining step (RDS) for Ni films in these electrolytes. Finally, combining the Fe and Co effects proved to boost the film’s activity beyond Fe3+’s limits.