Performance improvement of direct methanol fuel cell through structural control of the electrode

Abstract

Direct methanol fuel cell (DMFC) is an attractive power sources for portable electronic devices due to its high specific energy and compactness. However, it has been widely recognized that several problems have yet to be solved for the utilization of this device. Much effort has been made so far for improvement of DMFC. Especially, improvement of activities of the catalyst, decrease of methanol crossover, management of the mass transfer, and improvement of the durability have been key issues. Another important consideration for improving performance of DMFC is the electrode structure and the interface between the membrane and the electrode. The performance of DMFCs can be improved by varying the microstructure of MEAs. This is a study on improvement of the performance of direct methanol fuel cells (DMFCs) through control of the electrode structure. In the first part of the study, the microstructures of the electrode are controlled using several nanostructured carbons. With this approach, it is desired that the catalyst utilization is enhanced by the increased interface between the electrode and the electrolyte, and by controlling of microstructure of the carbon supports. It is also desired that the enhanced space and pores inside the electrode enhance the mass transport of the reactants and the products. First, vapor-grown carbon fibers (VGCFs) were added to the anode catalyst layer of a DMFC to improve the cell performance through structural modification of the catalyst layer. The amount of VGCF varied up to 6 wt.% with respect to the weight of the PtRu black catalyst that was used. A catalyst layer with 2 wt.% VGCF loading showed the best cell performance. The porosity of the catalyst layer was increased by the addition of the fibers. This was clearly observed in pore diameters less than $1\mum$. Sub-micron pore diameters are significant as they relate to micro-diffusive transport, compared to the macro-diffusion experienced by the large pores in the...