High Entropy (CoFeMnCuNiCr)₃O₄ Nanoparticles Anchored on Graphene-Based Supports for High-Performance Oxygen Evolution Electrocatalysis

High-entropy materials provide an interesting route for developing highly active electrocatalysts owing to their tunability and numerous active sites; however, their performance can be further improved with interfacial engineering in nanocomposite catalysts. In this study, (CoFeMnCuNiCr)3O4 high-entropy oxide (HEO) nanoparticles were synthesized and grafted onto graphene (HEO–G), graphene oxide (HEO–GO), and reduced graphene oxide (HEO–rGO) supports. X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) confirmed the formation of a nearly single-phase inverse spinel-type HEO. The HEO nanoparticles were more homogeneously distributed on GO and rGO than on G, likely due to the absence of critical functional groups in G, which limits strong interfacial interactions. The resulting HEO-based nanocomposites were evaluated as electrocatalysts for the oxygen evolution reaction (OER), exhibiting outstanding catalytic activity. Among them, HEO–rGO demonstrated the best performance, achieving an overpotential of 290 mV at 10 mA/cm2 with a Tafel slope of 86 mV/dec In comparison, the overpotential and Tafel slope values were 770 mV and 138 mV/dec for HEO, 380 mV and 92 mV/dec for HEO–G, and 827 mV and 112 mV/dec for HEO–GO, respectively. The exceptional catalytic performance of HEO–rGO is attributed to the intrinsic properties of HEO, its abundant oxygen vacancies, and the effective suppression of nanoparticle aggregation on rGO. Additionally, the proper electrical conductivity of rGO enhances charge transfer, further boosting OER activity.