UBC Theses and Dissertations
Direct methanol fuel cell with extended reaction zone anode : PtRu and PtRuMo supported on fibrous carbon Bauer, Alexander Günter
The direct methanol fuel cell (DMFC) is considered to be a promising power source for portable electronic applications and transportation. At present there are several challenges that need to be addressed before the widespread commercialization of the DMFC technology can be implemented. The methanol electro oxidation reaction is sluggish, mainly due to the strong adsorption of the reaction intermediate carbon monoxide on platinum. Further, methanol crosses over to the cathode, which decreases the fuel utilization and causes cathode catalyst poisoning. Another issue is the accumulation of the reaction product CO₂ (g) in the anode, which increases the Ohmic resistance and blocks reactant mass transfer pathways. A novel anode configuration is proposed to address the aforementioned challenges. An extended reaction zone (thickness = ∼100-300 µm) is designed to facilitate the oxidation of methanol on sites that are not close to the membrane-electrode interface. Thus, the fuel concentration near the membrane may decrease significantly, which may mitigate adverse effects caused by methanol cross-over. The structure of the fibrous electrode, with its high void space, is believed to aid the disengagement of CO₂ gas. In this thesis the first objective was to deposit dispersed nanoparticle PtRu(Mo) catalysts onto graphite felt substrates by surfactant mediated electrodeposition. Experiments, in which the surfactant concentration, current density, time and temperature were varied, were conducted with the objective of increasing the active surface area and thus improving the reactivity of the electrodes with respect to methanol electro-oxidation. The three-dimensional electrodes were characterized with respect to their deposit morphology, surface area, composition and catalytic activity. The second objective of this work was to utilize the catalyzed electrodes as anodes for direct methanol fuel cell operation. The fuel cell performance was studied as a function of methanol concentration, flow rate and temperature by using a single cell with a geometric area of 5 cm². Increased power densities were obtained with an in-house prepared 3D PtRu anode compared to a conventional PtRu catalyst coated membrane. Coating graphite felt substrates with catalytically active nanoparticles and the utilization of these materials, is a new approach to improve the performance of direct fuel cells.
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