Ionic mobility inorganic membrane

Those critical functions of membrane for DMFC are simple but most important. Required functions are ionic conductivity, electrical insulation, gas and liquid (especially methanol) tightness, and chemical and mechanical stability. As indicated in Fig. 13.2, ohmic polarization is mainly due to the ionic resistance of membranes, but the low open circuit potential of cathode is also mainly coming from the voltage drop by mixed potential made of fuel crossover through the membrane. The low cost of material and process is also another factor in terms of commercialization. Especially for mobile applications, membranes have the additional function for mass balance of liquid fuel and water products circulated out of or through the membrane. In this manner, alternative membranes are under development and researchers are focused on four types perfluorinated and partially fluorinated membranes hydrocarbon and composite and other ionomer modifications inorganic materials. The current state of the art and technical approaches to these materials are discussed in detail elsewhere in this volume. 

As described earlier, aliphatic polymers that are used as base material for PEMs are the commonly used membranes such as PVA, PVDF, and PMMA. In general, there are two means to increase the ionic conductivity of the PEMs (1) suppression of crystallization of polymer chains to improve polymer chain mobility and (2) increase in the carrier concentration. To realize these processes, they can be composited with other polymers or inorganic materials. Besides, copolymerization and cross-Unking techniques are also two important procedures for membrane synthesis/preparation. 

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