The proton conductivity of Nafion 117 was measured under various conditions of humidity and temperature usin a four-electrode ac impedance method. The conductivity of this membrane without heat-treatment was ca. 7.8 X 10 S cm' at ambient temperature and 100% relative humidity; it varied strongly with the humidity and heat-treatment of the membrane. After heat-treatment, the membrane showed a slight dependence of conductivity on temperature. From 21 to 45°C, its conductivity at a given relative humidity decreased with increasing temperature, while from 45 to 80°C it increased with temperature.Nafion 117® is a proton conducting ion-exchange membrane which is now receiving much attention due to its use as an electrolyte in the polymer-electrolyte-membrane fuel cell (PEMFC), which is of great interest for electric vehicle propulsion.' The performance of the PEMFC is strongly dependent on the humidification of the membrane, since membrane resistance changes drastically with water content. The water balance of the fuel cell is also extremely complicated. During the cell reaction in the PEMFC, the anode side (fuel side) of the membrane is readily dried up by the electro-osmotic drag of the proton, while the water produced in the cathode reaction diffuses back to the anode side. Analysis of the performance of a PEMFC requires reliable conductivity data for the membrane electrolyte at different humidities in combination with water uptake,4-1 water diffusion,8 gas diffusion properties,914 etc.

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The changes in structure and kinetics during charge of the porous PbO2 electrode have been studied by means of electrochemical and structure characterizing methods. It was found that the potentiostatic charge current after an initial period of growth, due to nucleation and growth of PbO2 , is proportional to the decreasing amount of remaining lead sulfate. The polarization curves have a Tafel slope of about 60 mV/decade at overvoltages lower than 0.1V and about 180 mV/decade at higher overvoltages. The form of these curves can be explained by a mechanism with two consecutive single‐electron transfer reactions. The results from these specific studies of the positive electrode and charge experiments with complete lead‐acid cells show that the fastest way to charge lead‐acid batteries is to charge at a constant cell voltage of a value just below that which leads to unacceptable gassing rates.