The Preparation and Performance of Bipolar Membranes

The properties required of bipolar membranes to be useful in practical applications are low electrical resistance at high current density, high water dissociation rates, low co-ion transport rate, high ion selectivities, good thermal and, most importantly, good chemical stability since the cation-selective layer of the bipolar membrane is in direct contact with an

acid and the anion exchange layer with an alkaline solution.

Low electrical resistance of the cation and anion exchange layer of the bipolar membrane can be obtained by using a strong acid, such as sulfonic acid groups, and a strong base, such as quaternary ammonium groups as fixed charges in high concentrations in the polymer matrix. To minimize the resistance of the interphase between the cation- and the anion-selec-tive layers the thickness of this interphase must be as thin as possible, as indicated earlier. There are various ways to prepare bipolar membranes with satisfactory properties. Most commonly, membranes are prepared as laminates with some kind of interphase which forms a transition region where the actual water dissociation takes place. In some membranes heavy metal hydroxides are deposited in the interphase to catalyse the water dissociation. However, tertiary ammonium fixed-charge groups at the surface of the anion exchange membrane seem to have the same effect.

A bipolar membrane with satisfactory properties can be prepared, e.g. as a laminate of highly perm-selective anion and cation exchange layers which have good alkaline and acid stability. An anion-selec-tive layer with the required properties can be obtained by reacting chloromethylated polysulfone dissolved in «-methyl pyrrolidone with the monoquater-nary salt of 4,4'-diazabicyclo-[2.2.2]-octane. The cation-selective layer can be prepared by introducing sulfonic acid groups as fixed charges into a poly-ether-ether-ketone matrix using chlorosulfonic acid. The co-ion transport and the swelling behaviour can be controlled in both layers by partial cross-linking. The properties of ion exchange membranes prepared following the above procedures are listed in Table 1.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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