Status of the development of a direct methanol fuel cell

In the past, most papers on direct methanol fuel cells (DMFC) reported about systems using pure oxygen instead of air supplied to the cathode. The status of the work on DMFC at Siemens was characterized by more than 200 mW/cm² at a cell voltage of 0.5 V under oxygen operation (4–5 bar abs.) at high temperatures (140°C). High oxygen pressure operation at high temperatures is only useful in special market niches. Low air pressure up to 1.5 bar abs. and therefore low operation temperatures in the range of 80–110°C are necessary technical features and economic requirements for widespread application of the DMFC. Today, our system produces 50 mW/cm² under air operation at low over pressure and at 80°C, while the cell voltage again amounts to 0.5 V. These measurements were carried out in single cells between 3 and 60 cm². First results for a cell design with an electrode area of 550 cm², which is appropriate for assembling a DMFC-stack, are shown. In the new cell it was possible to achieve the same power densities as in the experimental cells at low air over pressure. Also a three-celled stack based on this design revealed nearly the same performance. At 80°C a power output of 77 W at a stack voltage of 1.4 V can be obtained in the air mode. The low pressure air operation results in a lower performance which must be compensated by future improvements of the activity of the anode catalyst and by an adequate membrane with a low methanol and water permeation, which would be a great progress for the DMFC.