Nickel-driven compositional modulation in high-entropy spinel oxide/ carbon black composite catalysts for efficient bifunctional oxygen reactions

Abstract

This study synthesized high-entropy spinel oxides, specifically (FeCoNiCrCu)3O4, using a diethylene glycolassisted hydrothermal method and air annealing. The electrocatalytic performance was optimized by adjusting the annealing temperature (400 - 900 degrees C) and nickel (Ni) content, maintaining a consistent cubic spinel structure. Higher temperatures improved crystallinity but caused secondary-phase segregation, while excessive nickel led to the formation of oxide by-products, thereby reducing solid-solution stability. Structural analyses confirmed the formation of a uniform spinel structure with entropy-stabilized metals. Electrochemical testing revealed that an annealing temperature of 500 degrees C and moderate nickel enrichment resulted in the most effective catalyst. Combining this catalyst with acid-treated carbon black enhanced electrical conductivity and active site availability, improving bifunctional oxygen catalysis. The catalyst also exhibited excellent durability with minimal degradation after extended use, demonstrating the potential of high-entropy spinel engineering in developing robust bifunctional oxygen electrocatalysts.