Composite Membranes for Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs), often regarded as a green energy source, have become a promising candidate to replace traditional power sources. One of the obstacles toward commercialization of PEM fuel cells is lack of high performance and low cost proton exchange membranes. The objective of this study was to develop and evaluate higher-performance, Nafion-based composite proton exchange membranes that are suitable for operating at higher temperatures (\u3e 85°C). Proton exchange membranes were prepared by adding silica and heteropolyacids (HPAs) to a proton-conducting polymer matrix, Nafion. The added silica powder particles, either by direct mixing or sol-gel reaction, were found to enhance the thermal stability and lower thermal expansion of the composite membranes. Incorporating HPAs into Nafion greatly increased the proton conductivity of Nafion and the single cell performance was also greatly improved. In order to prevent HPA leaching, Y zeolite was used to encage HPA molecules inside its supercages. A templating mechanism was also used to trap HPAs with silica gels. Membranes and membrane-electrode assemblies (MEAs) with encaged HPAs were studied in light of HPA\u27s effects on the proton conductivity, thermal stability, thermal expansion coefficient, single cell performance, micro-morphology (SEM), and acid leaching. A nonelinear equation from fitted experimental data was proposed to model the relationship between proton conductivity and the acid doping level. The results showed that Y zeolite and silica gel can be used to prevent HPA from leaching by water. In order to increase the mechanical properties and water uptake properties, hydrophilic, expanded PTFE (ePTFE) was used as the scaffold material for PEM