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.
Ruthenium dioxide as electrocatalyst on an activated cathode for chlorate production was investigated with respect to its activity towards hydrogen evolution, hypochlorite reduction, and chlorate reduction, respectively. Investigations were made in the presence, as well as in the absence, of a chromium hydroxide film in 1M
normalNaOH
and in typical chlorate electrolyte. Low overvoltages for hydrogen evolution were found and, at technical current densities, an effect of catalyst coating thickness. Commercial DSA® electrodes with
RuO2
as the active compound were tested as cathodes and were less active but more stable than the coatings produced by us. Hypochlorite and chlorate were reduced in the absence of chromate, chlorate reduction being fast on ruthenium dioxide compared to the other electrode materials and by far the dominating cathodic reaction in chlorate electrolyte without chromate and hypochlorite at 70°C, 3 kA/m2.
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