Proton-exchange membrane fuel cells (PEMFC) have attracted immense attention as an efficient, lightweight and environmentally-friendly power source to meet growing worldwide energy demands. The water management in a fuel cell, especially at high temperatures, is crucial for the cell performance. To improve the water management of proton exchange membranes, a novel composite membrane was developed incorporating perfluorosulfonic acid (PFSA) polymer with a zeolite-coated porous substrate, providing excellent performance even under high temperatures and a dry environment. This thesis provides a better appreciation of the relationship between water uptake and cell performance in these confined PFSA-zeolite structures. The dynamic processes involving water, including adsorption on ze...[ Read more ]

Proton-exchange membrane fuel cells (PEMFC) have attracted immense attention as an efficient, lightweight and environmentally-friendly power source to meet growing worldwide energy demands. The water management in a fuel cell, especially at high temperatures, is crucial for the cell performance. To improve the water management of proton exchange membranes, a novel composite membrane was developed incorporating perfluorosulfonic acid (PFSA) polymer with a zeolite-coated porous substrate, providing excellent performance even under high temperatures and a dry environment. This thesis provides a better appreciation of the relationship between water uptake and cell performance in these confined PFSA-zeolite structures. The dynamic processes involving water, including adsorption on zeolite and molecular exchange at the zeolite/PFSA interface, were studied using attenuated total reflection Fourier transform infrared spectroscopy, micro-Raman spectroscopy, and quartz crystal microbalances. The effect of confinement on fuel cell performance was also investigated by regulating the pore size and porosity of the substrate. The results suggest that the PFSA chain is rearranged within confined spaces to facilitate proton transport, while zeolites promote water absorption and retention within the membrane. Several water-retaining zeolites were used to fabricate the composite membrane (referred as PSFA/zeolite/Sil-1), and the PFSA/Hβ/Sil-1 performed best with a maximum power density (MPD) of 602 mW/cm² at 60 °C and tolerated operation at up to 110 °C under dry conditions. Also, Pt-embedded zeolites were employed to prepare confined PFSA/Pt-zeolites/Sil-1 composite membranes, which not only retain water by adsorption but also generate water by catalysis. These membranes displayed outstanding performance in the absence of a humidifier during cell operation, especially at high temperature. The MPD of PFSA/Pt-Hβ/Sil-1 MEA is up to 690 mW/cm² at 60 °C and 169 mW/cm² at 110 °C. In addition, metal-organic frameworks (MOFs), another category of microporous material, were employed to fabricate the composite membrane.