Iron in the Presence of Iridium for Oxygen-Evolution Reaction under Alkaline Conditions

Abstract

The potential of the oxygen-evolution reaction (OER) to serve as a vital source of electrons for reducing water, carbon dioxide, and ammonia is an area of intense research. Among the numerous catalysts investigated for the OER, Ir compounds have emerged as particularly promising candidates. A notable highlight of this study is the concurrent OER activity of both Ir and Fe. Remarkably, Ir independently exhibits high OER activity, even at exceedingly low overpotentials, establishing its distinctiveness among other metal oxides. Under alkaline conditions, the presence of both Fe and Ir (hydr)oxides in OER systems introduces complexity, given that Fe (hydr)oxides are also known for their efficiency in the OER. This combination of elements creates a multifaceted reaction environment, where the unique properties of each component interact, influencing the overall OER process. In this study, the focus is on investigating the OER process on an Ir wire in an alkaline environment (with pH 13 and 14) in the presence of K2FeO4. To gain a comprehensive understanding of the reaction, various techniques, such as electrochemical methods, X-ray diffraction (XRD), electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM), were employed. Following an in-depth investigation and detailed analysis of the interaction between K2FeO4 and an Ir wire, it was observed that the activity of the OER increased at overpotentials exceeding 320 mV. The observed improvement was limited to cases where Fe species had deposited on the surface of the Ir wire. The Tafel slopes were found to be 196.10 (149.20) and 102.16 (56.30) mV/decade for the Ir electrode in 0.10 M (1.0 M) KOH, in the absence and presence of K2FeO4, respectively. XAS analysis revealed the presence of the FeHyOx species on the surface of IrO2. These experiments indicate that Fe and Ir sites can independently catalyze the OER without exhibiting any synergistic interaction between them.