The fuel cell technology commercialization is greatly dependent on the efficiency, cost, and durability of the fuel cell stacks. These are coupled with the effectiveness of the thermal and water management of polymer electrolyte membrane fuel cell (PEMFC) systems. The conventional liquid-cooled PEMFC systems include several balance of plant components like humidifiers, compressors, heat exchangers, etc. for an efficient operation leading to overall increased cost. The open-cathode PEMFC systems on the other hand use minimal auxiliary components by using ambient air as an oxidant as well as a coolant for extracting the heat away from the system. They offer lower system size and easier operation, with the main tradeoff being low efficiency. This thesis aims to investigate novel strategies for the development of high-performing open-cathode systems by using a computational modelling approach followed by experimental investigations. Firstly, a comprehensive, three-dimensional computational fuel cell model is developed, validated, and utilized to study the operational and hygrothermal behaviour of an open-cathode PEMFC at various ambient conditions compared to conventional liquid cooled cells. Moderate self-heating followed by membrane drying is found to be the key contributors towards lower cell performance for open-cathode cells while in operation at moderate-to high current densities and high air flow rates. At the component level, the water sorption/desorption rate constant (γ) for the ionomer is found detrimental to the overall cell performance; the current density at 0.6 V is found to increase remarkably by 130% by reducing γ from 10 s-1 to 0.1 s-1 under given ambient air conditions. This is accomplished through enhanced water retention and membrane hydration at elevated temperature. On further investigation, the strategic cathode catalyst layer (thin, high Pt/C ratio, high ionomer loading), cathode microporous layer (thin, high porosity), and membrane (thin) design is found to enable collective improvements in kinetics, oxygen mass transport, ohmic resistance, self-heating, and water retention in the ionomer phase. Lastly, these findings from the computational model are experimentally validated and a current density rise of 88% at 0.6 V and 53% at 0.4 V is achieved by the strategically designed membrane electrode assembly for open-cathode cells offering increased power density.
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Thesis advisor: Kjeang, Erik
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