Promotional effects of Ir addition in carbon-supported Pt5Rh electrocatalysts for the electrooxidation of ethanol at room temperature

Abstract

The high CO2 selectivity of Pt-Rh catalysts in the ethanol electrooxidation reaction has been known for some time. However, this high selectivity is often realized at the expense of catalytic activity. This study investigates the use of Ir modification to improve the performance of Pt-Rh catalysts. Specifically a series of Vulcan XC-72 carbon-supported Pt 5Rh1Irx catalysts were prepared by the NaBH4 reduction of the metal precursors in ethylene glycol. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed good dispersion of ∼2.5 nm Pt-Rh-Ir nanoparticles on the carbon support. Evaluations of catalytic activity in 1 M ethanol solution in 0.1 M HClO 4 by cyclic voltammetry (CV), polarization measurements, and chronoamperometry (CA) all indicated Pt5Rh1Ir 0.6/C as the catalyst composition with the highest current density between 0.4 and 0.7 V. Electrochemical impedance spectroscopy (EIS) detected a decrease in the charge transfer resistance after the Ir modification, which could be attributed to an Ir-promoted, more facile cleavage of the C-H bonds in the ethanol molecule. © 2011 American Chemical Society.