Synergistic Multimetal Effects in a High-Entropy Perovskite Oxide Anchored on Reduced Graphene Oxide for Accelerated Water Oxidation

Water electrolysis is a key technology for sustainable energy conversion and hydrogen generation. Recently, high-entropy oxides (HEOs) have emerged as promising materials because they allow tuning of structural, electronic, and catalytic properties in multifunctional systems. Here, we report the synthesis of a multicomponent La(FeCoCuTiNiMnMgSnZn)O₃ perovskite, and its hybridization with reduced graphene oxide (rGO) to form a robust La(FeCoCuTiNiMnMgSnZn)O₃-rGO nanocomposite. Structural characterization confirms the formation of a single-phase cubic perovskite structure with a uniform cation distribution and a slight lattice expansion compared with LaTiO₃. In addition, HEO nanoparticles are homogeneously dispersed on the rGO sheets. High-resolution XPS analysis also reveals a defect-rich surface with mixed metal valence states, which interact with the conductive carbon network. Electrochemical measurements show that the La(FeCoCuTiNiMnMgSnZn)O₃-rGO nanocomposite exhibits superior oxygen evolution reaction (OER) activity. It reaches a current density of 30 mA cm^-2 at a lower overpotential and shows a Tafel slope of 81.9 mV dec^-1. The catalyst also demonstrates good stability during 8 h of continuous operation. The enhanced performance is attributed to the combined effect of multiple metal elements in the high-entropy lattice, improved charge transport through the rGO network, and the presence of many active sites created by surface defects. These results show that combining HEOs with conductive carbon materials is a useful strategy for developing efficient and durable electrocatalysts for the OER.