The kinetics of O2 electroreduction on Pt in concentrated trifluoromethane sulfonic acid (TFMSA) have been investigated at elevated temperatures up to ∼90°C, using microelectrode technique, and the results compared with those previously obtained by similar measurements in concentrated H3PO4 . The activation energies for the reaction in ∼9.5M, 6.0M, and 3.0M TFMSA were, respectively, 17 kJ mol−1, 20 kJ mol−1, and 29 kJ mol−1, as compared to the value of ∼66 kJ mol−1 in 98 weight percent (w/o) H3PO4 . The exchange current densities and the diffusion‐limiting current densities in concentrated TFMSA solutions were, respectively, three and two orders of magnitude higher than the corresponding quantities obtained in 98 w/o H3PO4 . The solubilities and diffusion coefficients of O2 in TFMSA solutions have been evaluated, and their role in the current‐potential behavior for O2 reduction in these electrolytes is discussed.

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The proton activity of phosphoric acid and trifluoromethane sulfonic acid is determined at 150 ~ and 90~ by electrochemical potential measurements. The transference number of ions required for the calculation of proton activity is determined by measuring the diffusion coefficients of ions using radiotracer techniques. The proton activity of TFMSA is determined to be higher than that of phosphoric acid at the temperature and concentration at which the acid fuel cell operates.

There is great enthusiasm for the development of high power density fuel cell systems for defense and civilian applications. Taking into consideration the main causes for efficiency losses--activation, mass transport and ohmic overpotentials--the only fuel cell systems capable of achieving high power densities are the ones with alkaline and solid polymer electrolyte. High power densities (0.8 W/cm2 at 0. Even higher power densitiesHistorically, the first type of fuel cell system to find a major application (auxiliary power source in the Gemini Space Vehicles) is the one with solid polymer electrolyte as the electrolyte. These fuel cell systems were developed by the General Electric Company. Since the sixties, great strides have been made in increasing the power density from 50 mW/cm2 to about 2-3 W/cmz. The latter performance was achieved at Ballard Technologies Corporation which used practically the same technology as General Electric CompanylUnited Technologies Corporation--Hamilton Standard. The platinum loading in these fuel cells is 4 mg/cm2 on each electrode.Research and Development at Los Alamos National Laboratory and in our laboratory has led to the attainment of high power densities (zl watt/cm2> in solid polymer electrolyte fuel cells with ten times lower platinum loading in the electrodes (i .e., 0.4 mg/cm2>. used to attain these goals are as follows:The necessary criteria and the methods (1) Extension of the three dimensional reaction zone by the impregnation of a proton conductor (i.e., the ion-exchange membrane) into the electrode structure. Hot pressing of the proton-exchange membrane and electrodes at a temperature above the glass transition temperature and at a pressure of 50 atm. Adequate humidification of the reactant gases by passing these gases through humidification chambers set at temperatures of 10°C for H2 and 5OC for oxygen or air higher than the cell temperature. Enhancement of the electrode kinetics of the hydrogen oxidation and the oxygen reduction reactions and particularly of the mass transport rates of the reactant gases to the electrode by operation at elevated temperatures and pressures, say 95OC and 5 atm. Localization of the platinum near the front surface of the electrode to reduce the thickness of the active layer and provide a higher concentration of platinum sites on the front surface to reduce mass transport and ohmic overpotentials within the porous electrode and at the electrodelelectrolyte interface.( 2 )

Dielectric studies on 2,4,6-tri-and penta-substituted phenols have been carried out in a polystyrene matrix. Two sets of absorption curves were observed for 2,4,6-tri-and pentahalogenophenols in widely separated temperature ranges. The high-temperature process was identified as molecular relaxation while the low-temperature process for all the halogenophenols is intramolecular. Both proton tunneling and group relaxation were considered as candidates for the intramolecular process, and the AHE values and the Eyring plots suggest that there was no need to invoke tunneling. There is a significant increment in these intramolecular AHE values between the 2,4,6-tri-and the pentahalogenophenols. Pentachlorobenzenethiol was also examined, and the AHE value for the intramolecular process is 12 kJ mol-' less than for the corresponding phenolic compound. This is related, at least in part, to the weaker type of intramolecular hydrogen bond formed by the SH relative to the OH group.