Comparative studies of a single cell and a stack of direct methanol fuel cells

Comparative studies have been conducted to observe the characteristics of a single cell and a stack of direct methanol fuel cells (DNFC) at ambient conditions. The maximum power density of a single cell was about 70 mW/cm(2) at 2 M methanol (CH3OH) of 3.75 cc/min and dry air of 250 cc/min at room temperature and atmospheric pressure. In a stack, on the other hand, the maximurn power density of the stack was 85 mW/cm(2) which was about a 20% higher value. This could be attributed to higher internal temperature than that of the single cell: the temperature of single cell increased up to 35 degrees C, while the highest temperature of the stack was 69 degrees C. This is because the cell temperature in DMFC was autonomously increased by exothermal reaction such as chemical oxidation of CH3OH and oxygen reduction. The temperature was strongly dependent on the number of unit cells in a stack and the amount of electric load applied. In DNFC stacks, the performance of an individual cell showed uneven distribution when the electric load was increased and it was mostly influenced by different local concentration of reactants and non-uniform temperature.