초록/요약

This paper reports the facile synthesis of highly single-crystalline IrO<inf>2</inf> nanowires grown on an Au microwire (IrO<inf>2</inf>NW-Au) and its reduced form (Ir/IrO<inf>2</inf>NW-Au); and their electrocatalytic activity for oxygen reduction reaction, H<inf>2</inf>O<inf>2</inf> reduction/oxidation, and dopamine (DA) oxidation. IrO<inf>2</inf>NW-Au, prepared by direct vapor transport process under atmospheric pressure, was reduced by H<inf>2</inf> gas flowing at 200°C. This additional modification resulted in the significant morphological changes from the smooth nanowire structures of IrO<inf>2</inf>NW-Au to substantially porous structures of Ir/IrO<inf>2</inf>NW-Au with sustaining the external nanowire frameworks. The compositions were also changed from mostly IrO<inf>2</inf> in IrO<inf>2</inf>NW-Au to the mixture of IrO<inf>2</inf> and Ir(0) metal in Ir/IrO<inf>2</inf>NW-Au. Ir/IrO<inf>2</inf>NW-Au showed highly enhanced and facilitated electrochemical reaction kinetics compared to IrO<inf>2</inf>NW-Au for ORR and H<inf>2</inf>O<inf>2</inf> reduction/oxidation. The ORR limiting-like current at Ir/IrO<inf>2</inf>NW-Au was measured to be ∼19-fold greater than that of IrO<inf>2</inf>NW-Au. In addition, the amperometric responses to varying H<inf>2</inf>O<inf>2</inf> concentration confirmed that Ir/IrO<inf>2</inf>NW-Au exhibited ∼8-fold (for H<inf>2</inf>O<inf>2</inf> oxidation) and ∼750-fold (for H<inf>2</inf>O<inf>2</inf> reduction) higher sensitivity than IrO<inf>2</inf>NW-Au. The observed enhanced activity of Ir/IrO<inf>2</inf>NW-Au could be attributed to the enlarged active surface area as well as the inherent electroactivity of Ir/IrO<inf>2</inf>NW material induced by co-existence of Ir oxide and metal. In contrast, more stable and decent anodic current responding to DA oxidation was measured at IrO<inf>2</inf>NW-Au than Ir/IrO<inf>2</inf>NW-Au, indicating IrO<inf>2</inf> rather than Ir(0) has higher catalytic activity for DA oxidation. © 2015 Elsevier B.V. All rights reserved.