Enhancing the Oxygen Evolution Reaction Activity of Sputtered Ni, NiO, and NiNiO Thin Films by Incorporating Fe

Abstract The effect of Fe‐containing alkaline electrolyte, on the oxygen evolution reaction (OER) activity of Ni electrocatalysts, has long been of interest as Fe increases the OER activity of Ni electrocatalysts. However, controversy exists as to whether it is surface or bulk Fe that is responsible for the increased activity. In this study, magnetron sputtering was employed to sputter Ni, NiO and NiNiO thin film electrocatalysts to study the effect that different concentrations of Fe in the electrolyte have on their OER activities. It was found that increasing concentrations of Fe increasingly enhanced the OER activity of these thin film electrocatalysts until the electrolyte was saturated with Fe. The lowest overpotential achieved is 279 mV (at 10 mA cm−2) for NiNiO cycled in KOH containing 1 mM Fe, with all three thin film electrocatalysts exhibiting overpotentials within the same range after 30 voltammetry cycles in 0.9 ppm Fe and 1 mM Fe. All Tafel slopes are between 36 and 45 mV dec−1 indicating similar kinetics for the samples cycled in different Fe concentrations. Energy‐dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy results show that Fe is found in the top layers of the electrocatalysts after cycling.