Impact of the rhenium substitution on the oxygen evolution reaction of spinel CoFe2O4

Abstract

Structure engineering is a powerful tool for tuning various properties and making CoFe₂O₄ (CFO) a prime candidate for electrocatalyst applications, especially in improving the oxygen evolution reaction (OER) performance. In this work, we explored rhenium substituents to replace cobalt and iron atoms of the CFO and obtained significant differences with the same doping level. The sol–gel process was employed to prepare the nanoparticles of Co_1−zRe_zFe₂O₄ and CoFe_2−zRe_zO₄ (z = 0, 0.05). A detailed structural evaluation using Mössbauer spectroscopy verified the pure phase cubic spinel-type structure with a noticeable change in morphology by substituting Re. The OER and electrochemical impedance spectroscopy (EIS) were performed and showed better performance in the Fe-site doped structure. To explain the differences in the OER performance of the samples, X-ray photoelectron spectroscopy (XPS) on all elements, low-temperature Raman, and the density of states simulated by density-functional theory (DFT) were performed. We found that Re actively changed the properties of the structures and the doping on Fe-site enabled more oxygen vacancy and a higher ratio of cations in octahedral sites, which led to enhanced catalytic performance. This work provides a deep insight into the mechanism that influences the OER properties with Re doped in different sites, indicating a promising application of CFO as a catalyst material.