Iridium-copper oxide nanotubes catalyzing pH-universal oxygen evolution reaction with highly improved activity and durability via elemental substitution

Nanotubes of Ir-Cu binary metal oxide with various composition ratios (Ir_xCu_1−xO_y with x = 0.64, 0.48 and 0.33) were prepared using electrospinning followed by thermal annealing. Ir_xCu_1−xO_y nanotubes were investigated to be composed of rutile IrO₂ phase where Cu substituted Ir sites. This elemental subsititution induced the amorphization and generation of oxygen vacancy defects in the rutile phase of Ir_xCu_1−xO_y nanotubes. Among Ir_xCu_1−xO_y series, Ir_0.48Cu_0.52O_y nanotubes, having a reduced noble Ir content by more than a half, showed the best activity for oxygen evolution reaction (OER) in pH-universal condition, and even outperformed the material containing only Ir, commercial Ir/C and the other Ir-based binary metal oxide catalysts found in the literature. Of importance, Ir_0.48Cu_0.52O_y presented an excellent stability during continuous OER for 20,000 s in all the acidic, neutral and alkaline media despite their amorphousness. The introduction of Cu into IrO₂ was beneficial for improving not only the OER catalytic activity but the durability along with cost-effectiveness.