The Catalysis of the Oxygen Evolution Reaction by Iron Impurities in Thin Film Nickel Oxide Electrodes

Abstract

The effects of iron coprecipitated into thin film nickel oxide electrodes or introduced in the 25 weight percent KOH electrolyte were studied by a combination of galvanostatic and open‐circuit decay methods. Effects on voltammetric behavior and on the oxygen overpotential were observed in thin film electrodes with as little as 0.01% iron present. The over‐potential was further lowered by 1% iron to the extent that the nickel oxide charge storage reaction was adversely affected. Higher concentrations of iron coprecipitated into a composite iron/nickel hydrous oxide dramatically catalyzed the oxygen evolution reaction by lowering the Tafel slope from about 70 mV/decade with no iron present to about 25 mV/decade with 10–50% iron. This composite oxide shows promise as an anodic electrocatalyst for alkaline electrolysis to produce hydrogen; the oxygen overpotential on thin film electrodes was over 200 mV lower than the overpotential with nickel oxide, itself, when polarized at 80 mA/cm 2 .