▎ 摘　　要

IrxV bimetallic nanoclusters assembled on reduced graphene nanosheets (IrxV/rGO) with different compositions (x = 2, 11, 14, 21) were synthesized by a simple surfactant-free solution phase process at varied ratios of IrCl3 and NH4VO3 precursors. The structural characterizations confirmed that the synthesized nanoclusters with a clean surface were densely and uniformly assembled on rGO nanosheets with an average size of around 2 nm. The electrochemical measurements demonstrated that the electrocatalytic activities of IrxV/rGO hybrids for the oxygen reduction reaction (ORR) in alkaline media depends on the contents of iridium and vanadium in the nanoclusters. Compared to the pure iridium nanoclusters supported on rGO (Ir/rGO) and other compositions of IrxV/rGO, the Ir2V/rGO exhibited the maximum current density of ORR and superior tolerance against methanol crossover. From the rotating disk (RDE) and rotating ring-disk electrode (RRDE) measurements, the ORR occurs on Ir2V/rGO mainly through an efficient four-electron pathway. Furthermore, based on the structural and electrochemical studies, such Ir2V/rGO hybrids have obvious advantages as cathode electrocatalysts, such as an enhanced surface area due to the small size of Ir2V nanoclusters and their high dispersion on rGO nanosheets, low cost because of the precious metal-free components, and high electrocatalytic performance for the ORR from the synergistic effect of the alloyed Ir-V crystalline phase. It is anticipated that the IrxV nanoclusters assembled on rGO can be used as promising Pt-free cathodes in alkaline fuel cells.