Au-Ir alloy nanofibers synthesized from Au-Ir/IrO₂ composites via thermal hydrogen treatment: Application for glucose oxidation

This paper reports the facile formation of the alloy nanofibers of highly immiscible Au and Ir with diverse composition ratios (denoted as TH₂_Au_xIr_1−x, x = 0.05, 0.10 or 0.33, relative molar content of Au precursor) and the application for direct glucose oxidation. First, the composite nanofibers consisting of Ir/IrO₂ fibrous main frames decorated with Au nanoparticles (denoted as Pre_Au_xIr_1−xO_y) were synthesized via electrospinning and calcination. Then, these composites were annealed under H₂ gas flowing and successfully transformed to Au-Ir alloy nanofibers along with IrO₂ reduction to Ir metal in the Ir/IrO₂ fibrous frames. Thermal H₂-treatments with varying temperatures and duration times confirmed that Au-Ir alloy production required an unusually low temperature ≥ 90 °C at which Au and Ir were completely alloyed within 1 min. This study suggests that the Au-Ir alloying and IrO₂ reduction occur simultaneously and promote each other. TH₂_Au_0.33Ir_0.67, with ∼50.4 % Au atomic %, was found to still have segregated Au phase, indicating the limited solubility (molar ratio of Au/Ir < 1). Alloyed TH₂_Au_0.10Ir_0.90 exhibited high electroactivity for glucose oxidation: a surprisingly low onset potential (<< −0.4 V vs SCE) and greatly enhanced oxidation current levels compared with Pre_Au_0.10Ir_0.90O_y and pure Au nanoparticles. The high activity of TH₂_Au_0.10Ir_0.90 was attributed to the higher surface area of Au and more favorable formation of catalytically active OH_ads in the Au-Ir alloy. Current study presents that Au-Ir alloys can be formed under moderate condition via thermal H₂-treatment and possess a feasibility for nonenzymatic glucose oxidation.