Characterization of the three-phase boundary in differently-synthesized membrane-electrode assemblies

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Direct methanol fuel cells (DMFC) will play a decisive role in the future energy market, since they are especially well-suited for mobile applications at ambient or near ambient temperatures. As the kinetics of the methanol electrooxidation at room temperature is rather low, recently more applied engineering aspects moved into the focus of current fuel cell research. In improving the attainable DMFC performances no longer only tailor-made nanoparticle catalyst are the main concern but also factors like electron conductivity, proton conductivity and mass transfer within the membrane-electrode assembly (MEA). These are strongly correlated with the MEA structure, its porosity, ionomer content and the accessibility of the catalytic active particles. The proposed Sino-German project will concentrate on the investigation of the three-phase boundary within differently-synthesized membrane-electrode assemblies. It will aim on the optimization of the MEA structure (main parameters see above) with respect to DMFC operation at low temperatures. Various carbon supports will be used for the synthesis, that differ in grain size, shape, acidity and other features (QIU). These will be fabricated into a membrane-electrode using a conventional spraying technique (QIU, STIMMING). The catalytic active Pt nanoparticles will be brought onto the respective carbon support before or even after the completed MEA manufacturing by a special adsorption method (QIU). The resulting MEAs will be characterized by a combination of several techniques, e.g. BET adsorption, X-ray diffraction, X-ray absorption spectroscopy and high-resolution SEM, that have already shown their suitability for MEA characterization (FUESS). In addition, transmission electron microscopy and electron energy loss spectroscopy will be applied to image the detailed structure of the catalyst-membrane interface. Subsequently, the MEAs will be tested in single cell tests to further elucidate the correlation between the specific MEA structure and the achieved activity. It is supposed that this combined approach as described above will help to further adapt the MEA structure to its respective application in direct methanol fuel cells.