Polymer electrolyte membrane fuel cells, known for their high energy density and efficiency, are used in portable devices, stationary power systems, and transportation. However, contact resistance remains a challenge. This issue is particularly pertinent to fuel cells because they comprise different layers made from various materials. The interfaces between these layers can make it difficult for electrons to pass through. The gas diffusion layer and microporous layer are particularly influential. The microporous layer, made of carbon black and polytetrafluoroethylene, is typically applied to the gas diffusion layer facing the catalyst layer, improving electrical contact and expelling excess liquid water.
Applying a double-sided microporous layer to the gas diffusion layer can enhance performance by reducing contact resistance while maintaining efficient mass transport. The microporous layer, coated on both sides of the gas diffusion layer, improves electrical contact between components but increases the thickness, creating a trade-off between electrical contact and mass transport. This thesis investigates these complexities, aiming to balance improved electrical contact with effective gas and liquid management for higher overall fuel cell performance.
The first research chapter examines the performance of double-sided microporous layer coated gas diffusion layers, compared to a conventional single-sided coated gas diffusion layer. Specifically, focusing on using two different conventional carbon blacks that make up the microporous layer. The investigation revealed that double-sided microporous layers are more effective in the fuel cell due to improved water management capabilities and enhanced electrical contact. Of the carbon blacks tested, Vulcan black outperformed Ketjenblack.
Building on these findings, the next study explored integrating novel carbon materials into the microporous layer, to further enhance the double-sided configuration. Graphene, known for its exceptional electrical properties, was introduced to see if it could mitigate the trade-offs associated with increased gas diffusion layer thickness. Vulcan black, graphene and a blend of the two, were used to make the microporous layer. The results showed that the optimal arrangement was found to be with Vulcan black facing the catalyst layer and graphene facing the bipolar plate.
Following this, the research aimed to replicate the beneficial crack structure provided by graphene facing the bipolar plate, by using pore-forming agents. Various quantities and particle sizes of pore formers were tested. These successfully altered the microporous layer's structure, permeability and pore size distribution, while maintaining good electrical conductivity.
Overall, this study concludes that the best gas diffusion layer performance comes from using graphene on the bipolar plate side and Vulcan black on the catalyst layer side, highlighting graphene's unique advantages.
