Properties of the Ionic Groups

The ion transport number quantifies the amount of charge that is transported through the ion exchange membrane by that specific ion. Several methods are available to determine the ion transport number. A static method derived from Henderson s equation determines the transport numbers under diffusion [204]. In this method, a two-compartment cell is separated by a membrane and each of the compartments is filled with a KOH solution, both of different concentration. The resulting potential over the membrane is measured and can be used to calculate the transport number using Henderson s equation [204]  

A dynamic method called Hittorf s method allows determining transport numbers under migration, a method comparable with a fuel cell under operation. The two compartments in the cell are separated by an ion exchange membrane and both compartments are filled with the same KOH solution (same concentration). A current is applied between the two electrodes on either side of the compartments. At the cathode, hydrogen and hydroxide are produced, while at the anode hydroxide is consumed and oxygen is produced. To maintain electroneutrality, the cations (K ) and anions (OH ) present in the solution migrate through the membrane from one compartment to the other. Anionic and cationic transport numbers f and f ) can subsequently be determined [20,205,206]  

ANION EXCHANGE MEMBRANES FOR ALKALINE FUEL CELLS 

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