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

Micro/nano-patterning of supported lipid bilayers: biophysical studies and membrane-associated species separation

Micro/nano-patterning of supported lipid bilayers (SLBs) has shown considerable potential for addressing fundamental biophysical questions about cell membrane behavior and the creation of a new generation of biosensors. Herein are presented several novel lithographic methods for the size-controlled patterning of SLBs from the microscale to the nanoscale. Using these methods, chemically distinct types of phospholipid bilayers and/or Escherichia Coli (E. Coli) membranes can be spatially addressed on a single microchip. These arrays can, in turn, be employed in the studies of multivalent ligand-receptor interactions, enzyme kinetics, SLBs size limitation, and membrane-associated species separation. The investigations performed in the Laboratory for Biological Surface Science include the following projects. Chapters II and III describe the creation of lab-on-a-chip based platforms by patterning SLBs in microfluidic devices, which were employed in high throughput binding assays for multivalent ligand-receptor interactions between cholera toxin B subunits (CTB) and ganglioside GM1. The studies on the effect of ligand density for multivalent CTB-GM1 interactions revealed that the CTB-GM1 binding weakened with increasing GM1 density. Such a result can be explained by the clustering of GM1 on the supported phospholipid membranes, which in turn inhibits the binding of CTB. Chapter IV characterizes the enzymatic activity of phosphatase tethered to SLBs in a microfluidic device. Higher turnover rate and catalytic efficiency were observed at low enzyme surface densities, ascribing to the low steric crowding hindrance and high enzyme fluidity, as well as the resulting improvement of substrate accessibility and affinity of enzyme catalytic sites. Chapter V presents sub-100 nm patterning of supported biomembranes by atomic force microscopy (AFM) based nanoshaving lithography. Stable SLBs formed by this method have a lower size limit of ~ 55 nm in width. This size limit stems from a balance between a favorable bilayer adhesion energy and an unfavorable bilayer edge energy. Finally, chapter VI demonstrates the electrophoretic separation of membrane-associated fluorophores in polymer-cushioned lipid bilayers. This electrophoretic method was applied to the separation of membrane proteins in E. Coli ghost membranes