Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power applications in view of their low weight and volume relative to other power sources.A liquid feed direct methanol fuel cell has been developed based on a proton exchange membrane electrolyte and Pt/Ru and Pt catalyzed fuel and air/O2 electrodes respectively.The cell has been shown to deliver significant power outputs at temperatures of 60 to 90* C. The cell voltage is near 0.5 V at 300 mA/cm 2 current density and an operating temperature of 90* C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode.Further improvemerits in performance appear possible by minimizing the methanol crossover rate.

Significant advantages in weight, volume, and overall system performance of fuel cells would result if high-energy organic substances such as methane and its derivatives can be made to undergo direct electro-oxidation at the electrodes of the fuel cell without having to be converted by some catalytic process to hydrogen. This study demonstrates three novel fuels for direct-oxidation-type fuel cells. These new fuels are dimethoxymethane (DMM, dimethyl orthoformate), trimethoxymethane (TMM, trimethyl orthoformate), and trioxane (1,3,5-trioxane). The electro-oxidation and electrosorption characteristics of these new fuels at Pt, Pt-Sn, and Pt-Ru electrodes and the performance of these fuels in direct-oxidation fuel cells is described. Sustained direct electrochemical oxidation of aqueous solutions of DMM, TMM, and trioxane at high current densities has been demonstrated for the first time in half-cells and liquid-feed polymer electrolyte fuel cells. The oxidation of these fuels leads to the formation of methanol and ultimately carbon dioxide. Cyclic voltammetry and steady-state studies suggest that the electro-oxidation processes occur by chemisorption steps followed by surface reactions of adsorbed intermediates. The electro-oxidation of trioxane is preceded by an acid-catalyzed hydrolysis step on Nafion and in sulfuric acid solutions. These new fuels are best used without further processing in direct liquid-feed polymer electrolyte fuel cells.

Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power applications in view of their low weight and volume relative to other power sources. A liquid feed direct methanol fuel cell has been developed based on a protonexchange membrane electrolyte and Pt/Ru and Pt-catalyzed fuel and air/02 electrodes, respectively. The cell has been shown to deliver significant power outputs at temperatures of 60 to 90 °C. The cell voltage is near 0.5 V at 300 mA/cm2 current density and an operating temperature of 90 °C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode. Further improvements in performance appear possible by minimizing the methanol crossover rate. Assessment of catalysts for the oxidation of methanolAnodic oxidation behavior of methanol was investigated in half-cells using both supported and unsupported catalysts at a loading of 0.5 mg/cm2. In these experiments Elsevier Sequoia SSDI 0378-7753(93)01780-L Across Conventional Lines Downloaded from www.worldscientific.com by PURDUE UNIVERSITY on 04/12/15. For personal use only.