Composite membranes with inorganic materials

In order to achieve more control of methanol crossover, composite membranes are synthesized. Organic-inorganic composite membranes comprising Nafion with inorganic materials silica, mesoporous zirconium phosphate (MZP) and mesoporous titanium phosphate (MTP) are made as proton-exchange-membrane electrolytes for direct methanol fuel cells (DMFCs) [206] with increase in proton conductivity and low methanol crossover. Composite membranes with mordenite incorporated in polyvinyl alcohol-polystyrene sulfonic acid blend tailored with varying degree of sulfonation also retards the methanol release kinetics considerably [199]. 

Nearly all of the commercially available membranes are based on Nafion. Nafion also has the largest body of literature devoted to its study because of its demonstrated industrial importance and availability. Nafion composite systems also have already become significant in both industrial and academic research. In composite structures, Nafion can be impregnated into an inert Teflon-like matrix (i.e. W. L. Gore membranes ), or inorganic additives can be added to a supporting Nafion matrix for improved physical or electrochemical properties (i.e. lon-omem °). Some critical aspects of Nation s molecular structure and physical properties will be briefly highlighted to provide a baseline for comparison with the other alternative materials discussed in this review. 

Membranes are used for a wide variety of separations. A membrane serves as a barrier to some particles while allowing others to selectively pass through. The pore size, shape, and electrostatic surface charge are fundamental to particle removal. Synthetic polymers (cellulose acetate, polyamides, etc.) and inorganic materials (ceramics, metals) are generally the principal materials of construction. Membranes may be formed with symmetric or asymmetric pores, or formed as composites of ultra thin layers attached to coarser support material. Reverse osmosis, nanofiltration, ultrafiltration, and microfiltration relate to separation of ions, macromolecules, and particles in the 0.001 to 10 pm range (Rushton et al. 1996). 

Fig. 8.10 Hydrogen flux data of a composite membrane incorporating a Group IVB-VB material. Sieverts Law is followed very weU and a permeability at 440°C of 2.3 10 mol m s Pa was achieved. The membrane, sealed with copper gaskets, was essentially 100% selective towards hydrogen showing no detectable leak to helium. The disk withstood 33 bar differential pressure (Copyright Wiley-VCH Verlag, GmbH Co. KGaA, 2006. Adapted with permission from [8], Nonporous Inorganic Membranes.)...

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