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

Abstract

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 (Ir_xMo_1−xO_y, x = 0.14, 0.36, 0.43 and 0.79) showed distinguishable crystallinity and phase compositions. Especially, the Ir_0.43Mo_0.57O₂ nanofibers showed amorphous-like structures with oxygen vacancies, which was further supported by EPR spectroscopy. Among the series of Ir_xMo_1−xO_y samples, Ir_0.43Mo_0.57O₂ 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 Ir_0.43Mo_0.57O₂ was consistently good regardless of the electrolyte concentration, particularly in acidic and alkaline regions. In addition, Ir_0.43Mo_0.57O₂ presented outstanding stability in all the tested pH ranges during continuous OER for 12 h. It is noteworthy that Ir_0.43Mo_0.57O₂, which contains noble Ir at less than half the total metal content, outperformed the oxide of Ir only (IrO_y) and commercial Ir/C, showing its feasibility as a cost-effective and pH-universal OER catalyst.