Direct electro-oxidation of dimethoxymethane, trimethoxymethane, and trioxane and their application in fuel cells

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.