Oxygen-vacancy rich IrxMo1-xOy nanofibers for oxygen evolution reaction: excellent pH-universal and electrolyte-concentration-independent catalytic activity

Binary mixed oxide nanomaterials containing iridium (Ir) and molybdenum (Mo) were synthesized by electrospinning followed by a thermal annealing process. The synthesized nanomaterials with various composition ratios (IrxMo1-xOy, x = 0.14, 0.36, 0.43 and 0.79) showed distinguishable crystallinity and phase compositions. Especially, the Ir0.43Mo0.57O2 nanofibers showed amorphous-like structures with oxygen vacancies, which was further supported by EPR spectroscopy. Among the series of IrxMo1-xOy samples, Ir0.43Mo0.57O2 with similar Ir and Mo contents had the maximum substitution effect between the high-valent Mo ions and low-valent Ir ions, inducing the facile formation of oxygen defects, and therefore, revealed notable enhancement in the electrocatalytic properties toward the oxygen evolution reaction (OER) in a wide range of pH, covering acidic, neutral and alkaline conditions. Interestingly, the OER catalytic performance of Ir0.43Mo0.57O2 was consistently good regardless of the electrolyte concentration, particularly in acidic and alkaline regions. In addition, Ir0.43Mo0.57O2 presented outstanding stability in all the tested pH ranges during continuous OER for 12 h. It is noteworthy that Ir0.43Mo0.57O2, which contains noble Ir at less than half the total metal content, outperformed the oxide of Ir only (IrOy) and commercial Ir/C, showing its feasibility as a cost-effective and pH-universal OER catalyst.