Alteration of the morphology and electrocatalytic activity of IrO2 nanowires upon reduction by hydrogen gas

Abstract

This paper reports the facile synthesis of highly single-crystalline IrO2 nanowires grown on an Au microwire (IrO2NW-Au) and its reduced form (Ir/IrO2NW-Au); and their electrocatalytic activity for oxygen reduction reaction, H(2)O(2)reduction/oxidation, and dopamine (DA) oxidation. IrO2NW-Au, prepared by direct vapor transport process under atmospheric pressure, was reduced by H(2)gas flowing at 200 degrees C. This additional modification resulted in the significant morphological changes from the smooth nanowire structures of IrO2NW-Au to substantially porous structures of Ir/IrO2NW-Au with sustaining the external nanowire frameworks. The compositions were also changed from mostly IrO(2)in IrO2NW-Au to the mixture of IrO2 and Ir(0) metal in Ir/IrO2NW-Au. Ir/IrO2NW-Au showed highly enhanced and facilitated electrochemical reaction kinetics compared to IrO2NW-Au for ORR and H(2)O(2)reduction/oxidation. The ORR limiting-like current at Ir/IrO2NW-Au was measured to be similar to 19-fold greater than that of IrO2NW-Au. In addition, the amperometric responses to varying H2O2 concentration confirmed that Ir/IrO2NW-Au exhibited similar to 8-fold (for H2O2 oxidation) and similar to 750-fold (for H2O2 reduction) higher sensitivity than IrO2NW-Au. The observed enhanced activity of Ir/IrO2NW-Au could be attributed to the enlarged active surface area as well as the inherent electroactivity of Ir/IrO2NW 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 IrO2NW-Au than Ir/IrO2NW-Au, indicating IrO2 rather than Ir(0) has higher catalytic activity for DA oxidation. (C) 2015 Elsevier B.V. All rights reserved.