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Zeolite-based micro fuel cells

Authors Kwan, Siu Ming
Issue Date 2008
Summary Fuel cell is an electrochemical conversion device. It produces electricity from fuel and an oxidant which reacts in the presence of an electrolyte. The proton-exchange membrane fuel cell (PEMFC) is particularly interesting for mobile applications and it is currently an important research topic in the leading automobile industries. PEMFC has also been developing as a power device for computers and mobile telephones. Hydrogen is a potential fuel for PEMFC because of its high electrochemical reactivity and practically zero pollution level. Since the challegenes of hydrogen storage and delivery for such applications have not been resolved, methanol becomes an alternative fuel for PEMFC. Currently, Nafion® is the most widely applied electrolyte in PEMFC but it suffers from high cost, swelling and loss of mechanical strengths in the presence of methanol. These problems lead to deterioration of membrane structure, resulting in poor performance in PEMFC. Methanol crossover can be remedied by chemical treatment, modification of polymer chain and addition of copolymers. Inorganic materials such as zeolites, metal oxides and clays were used as fillers of Nafion membrane to decrease methanol permeation. Pure zeolite material as proton-exchange membrane was applied for developing a novel conceptual micro fuel cell using zeolite micromembrane as electrolyte in this dissertation. Silicalite-1 and ZSM-5 micromembranes were fabricated via microelectronic fabrication technology. The whole micromembrane unit was made of forty-nine micromembrane arranged in a 7 x 7 square array. Each micromembrane measured 0.062 mm2 and gave a total membrane area of 3.062 mm2. Molecular sieving was a clearly evidence from the single gas permeation, which indicated that the zeolite micromembrane was relatively free of defects, i.e. the primary gas transport was through the zeolite pores. Proton transport measurement showed that zeolite micromembrane exhibited comparable proton flux as the commercial Nafion® 117 membrane. HZSM-5 membrane-electrolyte-assembly (MEA) was prepared by a modified gluing method and compared with the conventional Nafion MEA in H2/O2 micro fuel cell and direct methanol fuel cell (DMFC). The result showed that zeolite MEA could achieve the same performance as the Nafion MEA in H2/O2 micro fuel cell and could deliver a modest power in direct methanol fuel cell. These results were very encouraging as it demonstrated the use of zeolite micromembrane as a proton-exchange membrane in μ-PEMFC and μ-DMFC for the first time ever.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008
Language English
Format Thesis
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