Electro-oxidation of ethanol on Pt, Rh, and PtRh electrodes. A study using DEMS and in-situ FTIR techniques

The electrochemical oxidation of ethanol on platinum, rhodium, and platinum-rhodium electrodes is studied using on-line differential electrochemical mass spectrometry (DEMS) and in-situ infrared spectroscopy (FTIR). The data were normalized using the oxidation of a CO monolayer in order to compare the activity of the different electrodes. Three products have been detected, namely CO2 and acetaldehyde (detected by DENIS) and acetic acid (detected by in-situ FTIR, since acetic acid is not volatile enough to be detected by DENIS). It is found that rhodium is the far less active electrocatalyst for ethanol electrochemical oxidation. Pure platinum and Pt90Rh10 present similar overall normalized current density, but Pt90Rh10 presents a better CO2 yield than pure platinum. The best CO2 yield is found for the Pt73Rh27 electrodes. The acetaldehyde yield decreases as rhodium is added to the electrode. The ratio CO2/CH3CH2O increases when rhodium is added to the electrode. The possible reasons for the different reactivity for the studied electrodes is discussed in terms of C-H bond activation and C-O bond coupling on the different surfaces.