The application of in-situ fourier transform infrared spectroscopy to the analysis of fuel cell anodes and membranes

Abstract

This work in this thesis reports fundamental studies on fuel cell electrocatalysis and membrane stability, and is primarily of relevance to direct ethanol alkaline fuel cells and proton-exchange membranes based on polybenzimidazole (PBI). During the first part of this project, in-situ FTIR spectroscopy was employed to investigate the electrochemical oxidation of ethanol at a polycrystalline Pt electrode in 0.1 M KOH at 25 and 50 oC. Initially, this part of the project was designed to provide a library of IR spectra of intermediates and products to facilitate the study of the electro-oxidation of small organic molecules at novel, non-noble metal anodes. However, the work on Pt has provided some unexpected insights into this area of electrocatalysis, particularly with respect to the role of intermediates bonded through oxygen rather than carbon, as well as of adsorbed CO. Acetate was the only product observed at lower potentials. Above the transition potential, where at least some of the areas of the thin layer in the spectro-electrochemical cell become acidic, acetaldehyde, acetic acid and a small amount of CO2 are produced. The temperature dependence of the production of acetaldehyde and acetic acid strongly suggests that the rate determining step is the removal of the first proton from the initially-adsorbed ethoxide species, and it was tentatively suggested that this is also the rds under alkaline conditions. Ethanol oxidation in alkaline solution at a Pb-modified Pt electrode was also investigated using FTIR. This study provided some very interesting data which support the suggestion that the adsorption mechanism of ethanol is substantially modified in the presence of Pb, with a carbon-bonded intermediate being favoured leading to facile scission of the C-C bond in ethanol. Carbonate formation took place at potentials close to the thermodynamic value and at higher potentials, when Pb was lost to solution, the mechanism of oxidation of ethanol reverts to that found on a normal polycrystalline Pt surface, with the primary product being acetate. During the second part of this project, undoped, cast films of PBI were investigated as a function of humidity using both H2O and D2O, and as a function of temperature up to 100 °C in order to better understand the IR response of this polymer, as well as to provide benchmark data for subsequent studies on acid doped PBI. Marked changes across the mid-IR range were observed during the uptake of water and D2O.