Electro-oxidation of ethanol at gas diffusion electrodes a DEMS study

The ethanol electro-oxidation at gas diffusion electrodes made of different catalysts, PtC, PtRu(1:1)/C, and PtSn(7:3)/C, were studied by on-line differential electrochemical mass spectrometry in a wide temperature range (30-90°C) as a function of the anode potential, the fuel concentration, and catalyst loading. The C O2 current efficiency (CCE) of the ethanol oxidation reaction (EOR) exhibits a maximum at about 0.6 V and decreases rapidly with further increasing potentials. The CCE for the EOR goes down with the increase in concentration of ethanol. CCE for ethanol oxidation reaction shows a strong increase with increasing catalyst loading. The CCE increases with increasing temperature, exceeding 75% at 90°C, 0.1 M ethanol, and 5 mg cm2 Pt catalyst loading. PtSnC shows high CCE, like PtC. But PtRuC exhibits very small CCE. Of the intermediates, acetaldehyde is quite active for further oxidation. But acetic acid is fairly resistant against further oxidation. Our results indicate that the C-C bond scission observed for the EOR with CCE in excess of 50% has to proceed in parallel with ethanol oxidation to either acetaldehyde or acetic acid, and not sequentially from acetic acid further on, as acetic acid cannot be oxidized any further.