Steam Effect on Conductivity

The proton conductivity of the H3PO4 imbibed PBI systems has been investigated by several groups. Steam presence was shown to have a positive effect on proton conductivity. Examples of the proton conductivity values recorded at different temperatures and relative humidity can be seen in Fig. 23. ° The proposed conductivity mechanism is proton migration from an imide site assisted by the counter anion and through the acid network based on the Grotthuss mechanism. 

H3PO4 recorded by several other research groups with increasing relative humidity  

The ionic conductivity of the PBI/PPy(50)coPSF membrane is depicted in Fig. 25 with respect to water partial pressure at various temperatures. The conductivity increases even by an order of magnitude with increasing steam partial pressure, especially at the higher temperature. At lower temperatures the conductivity is approaching asymptotically its maximum value already at Ph2o values of 10 kPa, while at 170°C the conductivity increases with a large slope even for Ph2o values above 10 kPa. 

Arrhenius plots of conductivity at various Ph2o values are depicted in Fig. 26. By fitting the data of Fig. 26 by Eq. (3) we can obtain the apparent activation energy Ea and the preexponential factor A which is directly related to the charge ionic capacity of the electrolyte  

Interestingly increases with increasing Pma, denoting an increase in the apparent activation energy for proton conduction which varies from 13-24 kJ/mol. Nevertheless the increase in proton conductivity is due to the increase in the preexponential factor A, which must be directly related to the increase of the ionic charge carriers concentration in the membrane. 

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