New electrolytes for direct methane fuel cells. Annual report, January 10, 1977-January 9, 1978. [Perhalogenated sulfonic acids]

The program is aimed at developing a fuel cell electrolyte for the direct oxidation of CH/sub 4/ and/or impure H/sub 2/ fuels. Work in the first year has focused on the di- and tribasic methane sulfonic acids CX/sub 2/(SO/sub 3/H)/sub 2/ and CX(SO/sub 3/H)/sub 3/ where X was H, F, or Cl. Synthesis of the halogenated acids proved to be more difficult than anticipated, and only three acids, viz. CH(SO/sub 3/H)/sub 3/; CH/sub 2/(SO/sub 3/H)/sub 2/; CCl/sub 2/(SO/sub 3/H)/sub 2/ were prepared in sufficient quantity for electrochemical testing. However, promising synthetic routes have been identified for the other acids. Cyclic voltammetry was used to study the adsorption properties of the acids and half cell tests with gas diffusion electrodes were used to determine their suitability as fuel cell electrolytes. Results are presented and discussed. Also a program has been under way to develop low Pt loading (1 mg cm/sup -2/) fuel cell electrodes. The objective was to achieve control over the mass transfer parameters of an electrode so that optimum structures could be designed for use with the new electrolytes. In the interest of reproducibility, the experimental electrodes incorporated only well characterized materials; all forms of carbon were omitted. Optimum performance with H/sub 3/PO/sub 4/ was achieved with electrodes made as follows. One mg cm/sup -2/ Pt black and 1 mg cm/sup -2/ TFE 30 were mixed and filtered onto porous TFE tape. The tape was pressed into Au plated Ta screen sintered for 10 minutes at 340/sup 0/C. Current vs potential curves for both anodic reactions (CH/sub 4/ and H/sub 2/ oxidation) and cathodic reactions (O/sub 2/ and air reduction) were superior to the curves obtained with an American Cyanamid electrode containing 25 mg Pt cm/sup -2/. (WHK)