Electrochemical characteristics of acid electrolytes for fuel cells. Annual report, August 1985-June 1986

Electrochemical characterization of a number of perfluorinated acids was carried out with the emphasis on identification of alternate acids that could replace the presently used H/sub 3/PO/sub 4/ in the H/sub 2/-O/sub 2/ fuel cells. The activity for O/sub 2/ reduction in the perfluorinated acids on smooth Pt and on high-surface-area Pt catalyzed electrodes (10% Pt on Vulcan XC-72) was examined. The cathode potential for O/sub 2/ reduction in CF/sub 3/PO(OH)/sub 2/ and (CF/sub 3/SO/sub 2/NHSO/sub 2/CF/sub 2/CF/sub 2/)/sub 2/ is significantly higher than H/sub 3/PO/sub 4/. The perfluorinated acids with two terminal functional groups do not wet Teflon and could be very useful in the fuel cells. The solubilities and the diffusion coefficient of O/sub 2/ in the perfluorinated acids are higher than H/sub 3/PO/sub 4/; over an order of magnitude and a factor of 5 to 6, respectively. The specific conductivities of the dilute perfluorinated acids are higher than phosphoric acid, whereas the specific conductivities of the concentrated perfluorinated acids, particularly the imides, are lower than 85% phosphoric acid. A number of the perfluorinated acids with longer fluorocarbon tail(s) tested as additives in 85% H/sub 3/PO/sub 4/.