Characterization of electro-oxidation catalysts using scanning electrochemical and mass spectral methods

Low temperature fuel cells have many potential benefits, including high efficiency, high energy density and environmental friendliness. However, logistically appealing fuels for this system, such as reformed hydrocarbons or alcohols, exhibit poor performance because of catalyst poisoning that occurs during oxidation at the anode. This research focuses on the analysis of several model fuels and catalyst materials to understand the impact of catalyst poisoning on reactivity. Two novel experimental tools were developed based upon the local measurement of catalyst performance using scanning, reactivity mapping probes. The Scanning Electrochemical Microscope (SECM) was used to directly measure the rate constant for hydrogen oxidation in the presence and absence of dissolved CO. The Scanning Differential Electrochemical Mass Spectrometer (SDEMS) was exploited to measure the partial and complete oxidation products of methanol and ethanol oxidation.; The reactivity of Pt and Pt/Ru catalysts towards the hydrogen oxidation reaction in the absence and presence of adsorbed CO was elucidated using the SECM. Steady state rate constant measurements in the absence of CO showed that the rate of hydrogen oxidation reaction exceeded 1 cms−1 . Steady state rate constant measurements in the presence of CO indicated that the platinum surface is completely inactive due to adsorbed CO. Addition of as little as 6% Ru to the Pt electrode was found to significantly improve the activity of the electrode towards CO removal.; SDEMS was used to study the electro-oxidation of methanol on Pt _xRu_y electrodes at different electrode potentials and temperatures. Screening measurements performed with the SDEMS showed that Pt_xRu _y electrodes containing 6–40% Ru had the highest activity for methanol oxidation. Current efficiencies for CO₂ were also calculated under different conditions.; SDEMS was also used to study the electro-oxidation of ethanol on Pt _xRu_y electrodes. The reaction was found to occur more slowly than the methanol oxidation reaction. Addition of 22%–40% Ru to the Pt electrode was found to increase the current densities and lower the onset potentials. The reaction was found to occur though a parallel path mechanism, which was confirmed by the detection of ethanol and acetic acid apart from CO₂.