Rapid Synthesis and Efficient Electrocatalytic Oxygen Reduction/Evolution Reaction of CoMn₂O₄ Nanodots Supported on Graphene

Transition-metal oxides have attracted extensive interest as oxygen-reduction/evolution reaction (ORR/OER) catalyst alternatives to precious Pt-based materials but generally exhibit limited electrocatalytic performance due to their large overpotential and low specific activity. We here report a rapid synthesis of spinel-type CoMn2O4 nanodots (NDs, below 3 nm) monodispersed on graphene for highly efficient electrocatalytic ORR/OER in 0.1 M KOH solution. The preparation of the composite involves the reaction of manganese and cobalt salts in mixed surfactant-solvent-water solution at mild temperature (120 °C) and air. CoMn2O4 NDs homogeneously distributed on carbonaceous substrates show strong coupling and facile charge transfer. Remarkably, graphene-supported CoMn2O4 NDs showed 20 mV higher ORR half-wave potential, twice the kinetic current, and better catalytic durability compared to the benchmark carbon-supported Pt nanoparticles (Pt/C). Moreover, CoMn2O4/reduced graphene oxide afforded electrocatalytic OER with a current density of 10 mA cm(-2) at a low potential of 1.54 V and a small Tafel slope of ∼56 mV/dec. This indicates that the composite of CoMn2O4 nanodots monodispersed on graphene is promising as highly efficient bifunctional electrocatalysts of ORR and OER that can be used in the areas of fuel cells and rechargeable metal-air batteries.