Growth of highly single crystalline IrO ₂ nanowires and their electrochemical applications

We present the facile growth of highly single crystalline iridium dioxide (IrO ₂) nanowires on SiO ₂/Si and Au substrates via a simple vapor phase transport process under atmospheric pressure without any catalyst. Particularly, high-density needle-like IrO ₂ nanowires were readily obtained on a single Au microwire, suggesting that the melted surface layer of Au might effectively enhance the nucleation of gaseous IrO ₃ precursors at the growth temperature. In addition, all the electrochemical observations of the directly grown IrO ₂ nanowires on a single Au microwire support favorable electron-transfer kinetics of [Fe(CN ₆)] ^4-/3- as well as Ru(NH ₃) ₆ ^3+/2+ at the highly oriented crystalline IrO ₂ nanowire surface. Furthermore, stable pH response is shown, revealing potential for use as a miniaturized pH sensor, confirmed by the calibration curve exhibiting super-Nernstian behavior with a slope of 71.6 mV pH ^-1.