Toward a comprehensive hypothesis of oxygen-evolution reaction in the presence of iron and gold

Abstract

This study investigates the effects of Fe on the oxygen-evolution reaction (OER) in the presence of Au. Two distinct areas of OER were identified: the first associated with Fe sites at low overpotential (≈330 mV), and the second with Au sites at high overpotential (≈870 mV). Various factors such as surface Fe concentration, electrochemical method, scan rate, potential range, concentration, method of adding K₂FeO₄, nature of Fe, and temperature were varied to observe diverse behaviors during OER for FeO_xH_y/Au. Trace amounts of Fe ions had a significant impact on OER, reaching a saturation point where the activity did not increase further. Strong electronic interaction between Fe and Au ions was indicated by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analyses. In situ visible spectroscopy confirmed the formation of FeO₄²⁻ during OER. In situ Mössbauer and surface-enhanced Raman spectroscopy (SERS) analyses suggest the involvement of Fe-based species as intermediates during the rate-determining step of OER. A lattice OER mechanism based on FeO_xH_y was proposed for operation at low overpotentials. Density functional theory (DFT) calculations revealed that Fe oxide, Fe-oxide clusters, and Fe doping on the Au foil exhibited different activities and stabilities during OER. The study provides insights into the interplay between Fe and Au in OER, advancing the understanding of OER mechanisms and offering implications for the design of efficient electrocatalytic systems.