Electrochemical characteristics of acid electrolytes for fuel cells

Electrochemical characterization of a number of perfluorinated acids was carried out with the emphasis on the identification of alternate acids which could replace the presently used H3PO4 in the H2-O2 fuel cells. The activity for O2 reduction in the perfluorinated acids on smooth Pt and on high surface area Pt catalyzed electrodes (10 percent Pt on Vulcan XC-72) was examined. The cathode potential for O2 reduction in CF3PO(OH)2 and (CF3SO2NHSO2CF2CF2)2 is significantly higher than H3PO4. 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 O2 in the perfluorinated acids are higher than H3PO4; 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 percent phosphoric acid. A number of the perfluorinated acids with longer fluorocarbon tails were tested as additivies in 85 percent H3PO4.