Effects of Iron Impurities and Content on Electrochemical Performance and Oxygen Evolution Selectivity of Nickel Catalysts for Ethanol Oxidation

Although performance enhancements due to trace Fe incorporation into Ni catalysts for the oxygen evolution reaction (OER) have been well documented, the effects of trace versus bulk Fe incorporation into Ni catalysts for the ethanol oxidation reaction (EOR)─a promising anodic alternative to OER─are unclear. Herein, we perform extensive cyclic voltammetry experiments on Ni-based thin films to show that trace Fe incorporation from electrolyte impurities has a minimal impact on EOR performance, while codeposited Fe significantly suppresses catalytic current (by half at 1.5 VRHE). Additionally, we apply operando electrochemical mass spectrometry (EC-MS) and directly observe the otherwise concealed onset potential of OER during EOR on the thin films, which surprisingly shows that the presence or absence of ethanol does not significantly impact OER, suggesting the reactions are catalyzed on different active sites. We also show that the previously observed low Faradaic efficiency of Ni for OER is time dependent─an important insight for the general interpretation of EC-MS data. Overall, our results further demonstrate the catalytic distinction between trace and bulk Fe incorporation in Ni and provide new insights into selectivity between EOR and OER.