Nanotubular Iridium-Cobalt Mixed Oxide Crystalline Architectures Inherited from Cobalt Oxide for Highly Efficient Oxygen Evolution Reaction Catalysis

Here, we report the unique transformation of one-dimensional tubular mixed oxide nanocomposites of iridium (Ir) and cobalt (Co) denoted as Ir_xCo_1-xO_y, where x is the relative Ir atomic content to the overall metal content. The formation of a variety of Ir_xCo_1-xO_y (0 ≤ x ≤ 1) crystalline tubular nanocomposites was readily achieved by electrospinning and subsequent calcination process. Structural characterization clearly confirmed that Ir_xCo_1-xO_y polycrystalline nanocomposites had a tubular morphology consisting of Ir/IrO₂ and Co₃O₄, where Ir, Co, and O were homogeneously distributed throughout the entire nanostructures. The facile formation of Ir_xCo_1-xO_y nanotubes was mainly ascribed to the inclination of Co₃O₄ to form the nanotubes during the calcination process, which could play a critical role in providing a template of tubular structure and facilitating the formation of IrO₂ by being incorporated with Ir precursors. Furthermore, the electroactivity of obtained Ir_xCo_1-xO_y nanotubes was characterized for oxygen evolution reaction (OER) with rotating disk electrode voltammetry in 1 M NaOH aqueous solution. Among diverse Ir_xCo_1-xO_y, Ir_0.46Co_0.54O_y nanotubes showed the best OER activity (the least-positive onset potential, greatest current density, and low Tafel slope), which was even better than that of commercial Ir/C. The Ir_0.46Co_0.54O_y nanotubes also exhibited a high stability in alkaline electrolyte. Expensive Ir mixed with cheap Co at an optimum ratio showed a greater OER catalytic activity than pure Ir oxide, one of the most efficient OER catalysts.