Characteristics of a direct methanol fuel cell based on a novel electrode assembly using microporous polymer membranes

This paper describes work carried out on novel electrode assemblies based on the use of microporous plastics for application in a direct methanol fuel cell. The results are compared with those from similar assemblies based on carbon paper. Studies of the oxygen reduction reaction for a platinum electrode carrying 0.88 mg Pt/cm2 on a spun-bonded polyethylene substrate gave a current density of 280 mA/cm2 at 0.64 V(SHE) at 75 °C (uncorrected for the ohmic potential drop). The platinum utilisation of this electrode system was found to increase with decreasing loading with the lowest loading of 0.08 mg Pt/cm2 giving almost 1.2 A/mg Pt at the same potential. Methanol electrodes based on these same membranes gave 266 mA/cm2 for a loading of 0.95 mg Pt+Ru (60:40) at 0.64 V(SHE) (uncorrected for the ohmic potential drop) running on methanol vapour at 75 °C. Again, decreasing the loading increased the catalyst utilisation with a 0.18 mg Pt+Ru (60:40) electrode giving over 1 A/mg Pt. Carbon paper-based electrodes showed the best overall performance toward methanol oxidation. However, these electrodes were found difficult to control both in half-cell and single-cell experiments because of leakage of the electrolyte. A single cell employing a circulating sulphuric acid electrolyte was used to evaluate the various electrode systems. In general, the cell output followed the behaviour predicted from the results of the half cells. Outputs ranged from 10 to 32 W/g Pt and from 5 to 15 mW/cm2 at 75 °C, depending upon the electrode system. The cell outputs were limited partly by the high resistance of the electrolyte which occurred as a result of the high interelectrode gap used for these experiments.