A significant advantage of direct methanol fuel cells (DMFCs) is the high specific energy of the liquid fuel, making it particularly suitable for mobile applications. Nevertheless, conventional DMFCs have to operate with excessively diluted methanol solutions to limit the methanol crossover and its detrimental consequences. Operation with diluted methanol solutions significantly reduces the specific energy of the power pack and thereby prevents it from competing with advanced batteries. In view of this fact, there exists a need to improve conventional DMFC system designs, including membrane electrode assemblies and the subsystems for supplying/removing reactants/products. This thesis focuses on experimental and theoretical investigation of mass transfer characteristics in DMFCs operatin...[ Read more ]

A significant advantage of direct methanol fuel cells (DMFCs) is the high specific energy of the liquid fuel, making it particularly suitable for mobile applications. Nevertheless, conventional DMFCs have to operate with excessively diluted methanol solutions to limit the methanol crossover and its detrimental consequences. Operation with diluted methanol solutions significantly reduces the specific energy of the power pack and thereby prevents it from competing with advanced batteries. In view of this fact, there exists a need to improve conventional DMFC system designs, including membrane electrode assemblies and the subsystems for supplying/removing reactants/products. This thesis focuses on experimental and theoretical investigation of mass transfer characteristics in DMFCs operating with highly-concentrated and neat methanol. First of all, a microfluidic-structured anode flow field has been developed. The fuel cell tests show that the innovative flow field allows the DMFC to achieve a good performance with a methanol concentration as high as 18.0 M. The remainder of the thesis is then focused on the study of neat methanol operating characteristics. To understand the role of water, a method that enables the water transport rate through the membrane to be in-situ determined has been developed. With this method, the effects of the MEA design and operating conditions on the water transport as well as its influence on the product distribution of the MOR, the anode overpotential and the cell internal resistance have been investigated. With the increased understanding of water transport characteristics, the design of the cathode gas diffusion layer has been optimized to improve both the water and oxygen management. To further increase the performance, a thin layer consisting of nanosized SiO₂ particles and Nafion ionomer is proposed to be coated onto each side of the membrane; the experimental results show that the added SiO₂ layers can upgrade the cell performance by 26%.

Keywords: Direct methanol fuel cell; Specific energy; Concentrated fuel; Neat methanol; Mass transport