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

In this study, high-entropy spinel oxides, including (Fe 0.2 Co 0.2 Ni 0.2 Cr 0.2 Zn 0.2 ) 3 O 4 , (Fe 0.15 Co 0.15 Ni 0.15 Cr 0.275 Zn 0.275 ) 3 O 4 , and (Fe 0.25 Co 0.25 Ni 0.25 Cr 0.125 Zn 0.125 ) 3 O 4 , 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, (Fe 0.25 Co 0.25 Ni 0.25 Cr 0.125 Zn 0.125 ) 3 O 4 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 (Fe 0.25 Co 0.25 Ni 0.25 Cr 0.125 Zn 0.125 ) 3 O 4 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. • Solvothermal annealing produced uniform, single-phase high-entropy spinel oxides. • FCN0.25CZ0.125 exhibited an optimized electronic structure with 32.2% oxygen vacancies. • FCN0.25CZ0.125/10G demonstrated enhanced charge transport and 268 mV OER activity. • FCN0.25CZ0.125/10G showed strong bifunctional durability with 93% OER and 91.7% ORR.