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 may replace the presently used H3PO4 in the H2-O2 fuel cells. The kinetics of O2 reduction in the clean perfluorinated acids on smooth Pt and on high surface area Pt calalyzed electrodes (10 percent Pt on Vulcan XC-72) was found to be much faster than in phosphoric acid. The potential of the O2 cathode in the micro-fuel cell utilizating some of the new acids particularly, CF3PO(OH)2, (CF3SO2)2NH, (CF3SO2)2CH2, and (DF3S)2NHSO2CF2)2 is 40 percent 60 mV 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 used as minor additives to 85 percent H3PO4 were found to improve significantly the performance of the oxygen cathode. The approach of achieving higher performance for the phosphoric acid fuel cell is very promising but is contingent on identifying surfactant-like additives with very low intrinsic vapor pressure and stability at elevated temperatures.