IrOx–Pt electrode for the electro-oxidation of ethanol in alkaline-type direct ethanol fuel cells: an excellent CO-tolerant catalyst

Abstract

In this study, an iridium-oxide-layer-deposited Pt surface (IrO_x–Pt) was explored as a catalyst for the ethanol oxidation reaction (EtOR) in an alkaline medium. To fabricate the catalyst, the cleaned Pt surface was scanned from 0 V to +1 V vs. Ag/AgCl (sat. KCl) in an Ir₂O₃·xH₂O colloidal suspension for 10 continuous cycles. The cyclic voltammogram recorded in the 0.1 M NaOH solution corroborated the presence of IrO_x as it showed the appearance of a distinct redox pair on the Pt surface, with E_pa at −0.31 V and E_pc at −0.27 V. Energy-dispersive mapping verified the uniform deposition of IrO_x on Pt, and X-ray photoelectron spectroscopy showed that IrO_x contained both Ir^III and Ir^IV species. The results of the cyclic voltammetry analysis indicated that the activity of the pure Pt catalyst towards the EtOR was approximately 1.3 times greater than that of IrO_x–Pt. However, the CO tolerance of the Pt catalyst was roughly 3.5 times lower than that of IrO_x–Pt. The results of the stability test indicated that the current density associated with EtOR on the IrO_x–Pt electrode experienced a decrease of approximately 18% with a standard deviation of 1.15% after 500 consecutive cycles. In contrast, the Pt electrode exhibited a decrease in activity of nearly 50% with a standard deviation of 1.53% under similar experimental conditions. The study of scan rate dependent voltammograms revealed that the electrode reaction was limited by mass transfer.