Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references. Also available in electronic version.

Proton Exchange Membrane Fuel Cells (PEMFCs) are widely regarded as the next generation of portable power production devices, with uses ranging from powering automotive vehicles to laptops and smartphones. PEMFCs convert oxygen and hydrogen into water and usable electricity and have no moving parts, meaning that they can reach overall efficiencies of 60%. However current Polymer Electrolyte Membranes only work efficiently below 80 C and at high humidity. At this low temperature, CO poisoning of the Pt electrocatalysts means that only high-grade fuel (low CO concentration ≤ 2 ppm) and high catalyst loading are required. This means that the overall cost of a PEMFC is prohibitively expensive. To dramatically the reduce cost and increase the efficiency of a PEMFC, new membranes are required which work at 120 C, at which point CO poisoning is no longer a dominating issue. In this thesis, the synthesis of novel organic/inorganic hybrid polyurethane Polymer Electrolyte Membranes (PEMs) with covalently bound phosphonic acid moieties (PA) made from cheap source materials have been reported, which, for the first time, demonstrate high conductivities at high temperatures, for example a PEM made from triethoxysilylpropyl isocyanate, polyethylene glycol, 4,4’-methylene diphenyl diisocyanate and PA displayed a conductivity of 3  10-2 S cm-1 at 120 C and 100% RH. The membranes also display good mechanical, thermal and chemical stability making them ideal candidate PEMs for the use in PEMFCs. However further work needs to be done to reduce the thickness of the membranes from their current thickness of 200 m to just 20-30 m, which would dramatically increase their efficiency when used in a PEMFC, by reducing the Area Specific Resistance and increasing the output (usable) power.

The dynamical characteristics and the structure of lithium in Nafion were investigated by solid state magic angel spinning nuclear magnetic resonance(MAS NMR). Variable temperature, longitudinal NMR relaxation time(T1), self-diffusion coefficients and rotational activation energy of various concentrations were determined. The distribution of the 7Li MAS NMR spectra of Nafion/Li represent the pore size, and T1 of Nafion/Li is slower than the bulk lithium solution, it implied the lithium were crowed in the pore(exchanged with the proton). Rotational activation energy illustrated the block level of lithium in different pores of Nafion. In the longitudinal NMR relaxation rate of various concentrations, instead, the type of bonding between lithium and water were different. The variable temperature experiments of 7Li MAS NMR spectra also illustrated the temperature about 60~66¢J result in the change of microstructure of Nafion.

The experimental tests and analysis of a fuel cell unit and a 150 W fuel cell stack are performance in this research. The experimental items in this study are various the types of flow channels, fasten torque, inlet gas pressure, Pt loading density, oxidizers, electron collector type etc. Through above a series of the tests, we can understand the key factors which influence the performance of the PEMFC. The experimental results can also provide us references when one assemble a fuel cell stack in future. PEMFC can start quickly at low temperature and achieves stable output voltage. When the 8 N-M torque is applied to fasten the reaction chamber, the contact resistance between electrode and electron collector reaches a minimum value. By designing the flow channel properly, the membrane hydration can remain a good state so that the conductivity of the proton exchange membrane can not be hinder. We found that the optimum channel among three types of the test channels is the conventional channel with the rib width 2 mm. When the output power is largest. Our experiments display that the increase of Pt loading in cathode can improve PEMFC performance. At certain voltage, there is a critical value in Pt loading. PEMFC performance can not be improved when Pt loading increases over this value. When the inlet pressure in cathode side increase to 10~20 psi higher than the pressure in anode side, the output power can improve apparently. Keyword: Proton exchange membrane, Pt loading, electron collector.

The research of a hydrogen proton exchange membrane fuel cell is performed under certain designing and operational conditions. The water management technique is incorperated into the experimental work. The cell voltage vs. the current densities are studied by changing the stack reactive temperatures, the gas inlet temperatures and pressures, and the relative humidities in hydrogen stream. Eventually, we hope that these experimental results can provide the information about the optimizing conditions of fuel cells so that they can be used to design a high power multiple-cell fuel cell stack. A membrane and electrode assembly (called MEA) which contains a proton exchange membrane Nafion 112, anode catalyst Pt 0.4 mg/cm2, and cathode catalyst Pt 1.0 mg/cm2 is used in this experiment. The gas flowing area is about 58% of the total area. A proper heating and humidification equipment is applied in this experimental system. The experimental results show that the cell voltage at low current density is slightly influenced by the hydrogen inlet temperature; however, the cell voltage at high current density is strongly influenced by the humidity ratio of hydrogen stream. Raising the hydrogen pressure and the oxygen pressure at the same time can increases the cell voltage, but it is no obvious effects on the cell voltage when the gas pressure increases to more than 2 atm. When air is used as a oxidizer, increasing the inlet air temperature always reduces the cell voltage. With the hydrogen stream at saturated temperature 80¢XC, the assembly torque of the stack at 4 N-m, and the stack temperature at 80¢XC, the single fuel cell stack can always generate the best cell voltages at most of the current densities. At this time, the cell voltage at current density 1 A/cm2 already can reach a value higher than 0.6 V.

Abstract The characteristics of PEMFC stacks in different designs and operational conditions are studied and manufactured in this thesis. There are many factors that affect the PEMFC performance. They include the familiar humidity, the torque, the inlet pressure, the geometries of inlet ports and the flow channels in reaction regions, the cell numbers of the stacks, the type of the oxidizer and its flow rate. To understand the performance characteristics of stacks the voltage and current density will be measured as well as the interior temperature of stacks in this research. The membrane exchange assembly (MEA) with Nafion 112, anode Pt 0.4 mg/cm² and cathode Pt 1.0 mg/cm² is used in these experimental works. The experimental results display that increasing the applied torque will reduce the contact resistance between bipolar plate and diffusion layer but increase the difficulty of gas penetrating into the reaction region beneath the bipolar rib. So proper torque is necessary to obtain the best voltage output. The voltage vs. current density also increases as the inlet pressure increases, but its effect will reduce when the inlet pressure increases over 2atm. The geometry and size of inlet port to each cell for a multi-cell stack will influence the voltage output, especially in high current density, so that special attention is needed in designing inlet port. When the air is used as an oxidizer, the fan with a high rotation speed is helpful in an open circuit design. The high air volume flow rate can avoid that the voltage output decays greatly in high current density. Increasing the cell number may cause extra internal resistance due to assembling improperly and reduce the voltage output. So special attention is also needed in assembling. Keyword: Proton Exchange Membrane Fuel Cell Stacks

Thesis (M.S.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 18).

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 63-65).