Dynamic Changes of an Anodized FeNi Alloy during the Oxygen Evolution Reaction under Alkaline Conditions

Abstract

An efficient and durable oxygen evolutionreaction (OER)catalystis necessary for the water-splitting process toward energy conversion.The OER through water oxidation reactions could provide electronsfor H2O, CO2, and N-2 reduction andproduce valuable compounds. Herein, the FeNi (1:1 Ni/Fe) alloy asfoam, after anodizing at 50 V in a two-electrode system in KOH solution(1.0 M), was characterized by Raman spectroscopy, diffuse reflectancespectroscopy (DRS), X-ray absorption spectroscopy (XAS), X-ray diffraction(XRD), scanning electron microscopy (SEM), energy-dispersive X-rayspectrometry (EDX), transmission electron microscopy (TEM), high-angleannular dark-field imaging (HAADF)-scanning transmission electronmicroscopy (STEM) and used as an efficient and durable OER electrocatalystin KOH solution (1.0 M). The overpotential for the onset of the OERbased on extrapolation of the Tafel plot was 225 mV. The overpotentialsfor the current densities of 10 and 30 mA/cm(2) are observedat 270 and 290 mV, respectively. In addition, a low Tafel slope isobserved, 38.0 mV per decade, for the OER. To investigate the mechanismof the OER, in situ surface-enhanced Raman spectroscopywas used to detect FeNi hydroxide and characteristic peaks of H2O. Impurities in KOH can adsorb onto the electrode surfaceduring the OER. Peaks corresponding to Ni(III) (hydr)oxide and FeO4 (2-) can be detected during the OER, but high-valentFeNi (hydr)oxides are unstable and reduce under the open circle potential.Metal hydroxide transformations during the OER and anion adsorptionshould be carefully considered. In addition, Fe3O4 may convert to & gamma;-Fe2O3 during the OER.This study aims to offer logical perspectives on the dynamic changesthat occur during the OER under alkaline conditions in an anodizedFeNi alloy. These changes encompass variations in morphology, surfaceoxidation, the generation of high-valent species, and phase conversionduring the OER.