Interplay of elemental configuration and graphene support in high-entropy spinel oxides for oxygen electrochemical reactions

Abstract

In this study, high-entropy spinel oxides, including (Fe0.2Co0.2Ni0.2Cr0.2Zn0.2)3O4, (Fe0.15Co0.15-Ni0.15Cr0.275Zn0.275)3O4, and (Fe0.25Co0.25Ni0.25Cr0.125Zn0.125)3O4, were synthesized using a solvothermal annealing method, and graphene-supported samples were subsequently prepared. Structural characterization confirmed the formation of a single-phase cubic spinel structure with homogeneous elemental distribution. X-ray photoelectron spectroscopy revealed composition-dependent differences in metal valence states and oxygen vacancy contents. Among the samples, (Fe0.25Co0.25Ni0.25Cr0.125Zn0.125)3O4 exhibited the highest oxygen vacancy fraction (32.2%) among the compositions. The introduction of graphene was associated with improved particle dispersion and electrical conductivity. Electrochemical measurements showed that the (Fe0.25Co0.25-Ni0.25Cr0.125Zn0.125)3O4 with 10 wt% graphene catalyst required an overpotential of 268 mV to reach a current density of 10 mA cm-2 for the oxygen evolution reaction, and exhibited a relatively large electrochemical surface area and lower charge-transfer resistance. Stability tests indicated that 93% of the initial OER current density and 91.7% of the oxygen reduction reaction current density were retained. This work presents a systematic investigation of composition and graphene support effects on the electrocatalytic behavior of High-entropy spinel oxides.