Single-Step Electrospun Ir/IrO₂ Nanofibrous Structures Decorated with Au Nanoparticles for Highly Catalytic Oxygen Evolution Reaction

Nanocomposites of gold (Au) and iridium (Ir) oxide with various compositions (denoted as AuxIr1–xOy, x = 0.05, 0.10, or 0.33, Au precursor molar ratio to Ir precursor) were synthesized via electrospinning and subsequent calcination method with two different solvent composition ratios of ethanol to N,N-dimethylformamide (DMF) in the electrospinning solution (ethanol/DMF = 70:30 or 50:50% v/v). Simple single-step electrospinning successfully fabricated a hierarchical nanostructure having Au nanoparticles formed on fibrous main frames of Ir/IrO2. Different solvent composition in the electrospinning solution induced the formation of main frames with distinct nanostructures; nanoribbons (AuxIr1–xOy-70) with ethanol/DMF = 70:30; and nanofibers (AuxIr1–xOy-50) with ethanol/DMF = 50:50. The pure Ir or Au counterparts (IrOy and Au) were also prepared by the same synthetic procedure as AuxIr1–xOy. Oxygen evolution reaction (OER) activities of as-synthesized AuxIr1–xOy were investigated in 0.5 M H2SO4 and compared to those of IrOy, Au, and commercial iridium (Ir/C, 20% Ir loading on Vulcan carbon). Among them, Au0.10Ir0.90Oy-50 exhibited the best OER activity, even better than previously reported catalysts containing both Ir and Au. The high OER activity of Au0.10Ir0.90Oy-50 was mainly attributed to the fiber frame structure and the optimal interfacial areas between Au and Ir/IrO2, which are electrophilic OER active sites. The stability of Au0.10Ir0.90Oy-50 was also evaluated to be much higher than that of Ir/C during OER. The current study suggests that the presence of Au on the Ir/IrO2 surface improves the OER activity of Ir/IrO2.