Characteristics of Mass Transport in Anion- Exchange Membrane Direct Ethanol Fuel Cells.

摘要

The primary objective of this thesis is directed at the understanding of mass transport phenomena in a next-generation fuel cell that is energized with ethanol - a sustainable, carbon-neutral transportation fuel. Radically different from conventional direct ethanol fuel cells (DEFCs) that use acid proton-exchange membranes and precious metal catalysts, this new DEFC uses alkaline anion-exchange membranes (AEM). We show the performance of AEM DEFCs is much better than that of PEM DEFCs. To further improve the cell performance, we focus on the understanding of mass transport behaviors through the membrane electrode assembly (MEA) and investigating the effect of each MEA component on the cell performance. We show experimentally that the cathode water flooding is still an important issue that affects the cell performance in AEM DEFCs although water is consumed at the cathode. To suppress the cathode water flooding, we investigate the effect of the cathode micro-porous layer on mass transport of water and oxygen and find that the use of a crack-free micro-porous layer can reduce the cathode flooding, hence improve the cell performance. To further understand the water transport through the AEM, we have developed a new method to measure water uptake and transport properties through the AEM. We also investigate the effect of polymer binders in the anode catalyst layer on mass transport of reactants and cell performance. To further enhance the anode mass transport, an integrated anode electrode structure that is composed of a nickel foam layer with thin catalyst films coated onto the skeleton of the foam is proposed and developed, which can significantly improve the cell performance. Finally, with the increased understanding of mass transport phenomena and with the improved MEA design, we show that the peak power density of the AEM DEFC can be as high as 111 mW cm-2 at 60 °C.