Electrochemical and transmission infrared spectroscopic studies of methanol oxidation reactions at platinum and platinum-ruthenium fuel cell catalysts

This thesis describes an ex situ approach using a micro-volume infrared transmission flow cell for quantitative determinations of CO2 dissolved in solutions following electrochemical oxidation reactions. Based on this novel technique, the investigation of the activity of electrodes toward methanol oxidation to CO2 is reported. As an in situ probe, infrared spectroscopy is quite sensitive to CO2 formation from electrochemical oxidation pathways of fuel cells. However, quantification of CO2 is made difficult by the optical properties of infrared spectroelectrochemical cells. The ex situ method demonstrated here provides CO: quantities, percent yields and formation rates, and probably a more accurate determination of the relationship between applied potential and CO2 formation rate compared to in situ infrared spectroscopy methods. Initially, the formation of CO2 from 0.1 M formic acid electrochemical oxidation was studied. The average yields of CO2 are close to 100 % across the range of potentials studied. The experimental results demonstrate the ex situ technique has sufficient sensitivity to determine CO2 in electrolyzed samples following 180 s reaction time, and also provides the ability to make repetitive measurements simply and rapidly.

Most work focuses on the formation of CO2 from 1.0 M methanol electrochemical oxidation on supported Pt and Pt-Ru catalysts on catalytically inert gold. Pt black, Pt-Ru black catalysts and Vulcan XC-72R carbon supported R and R-Ru catalysts have been considered. The rate of CO2 production increased as potential was made more positive up to 0.9 V (vs. a KCI saturated Ag/AgCI reference electrode). The CO2 yields decreased at lower potentials, as partially oxidized species adsorbed onto the catalyst surface. Methanol oxidation has resulted in above 80 % CO2 yields on Pt-Ru catalysts at all potentials between 0.2 V and 0.7 V; and 60-80 % CO2 yields at potentials between 0.6 V and 0.9 V and 40-60 % CO2 yields at potentials between 0.4 V and 0.5 V on Pt catalysts. The lower CO2 yields in the pure R case, which indicated incomplete methanol oxidation, are predictably ascribed to more evident adsorption of partial oxidation products and larger formation of soluble intermediates. Under the conditions studied. R-Ru based nano-cluster electro-catalysts provide the greatest activity for the electrochemical oxidation of methanol.