Ion Exchange Membrane for Reverse Electrodialysis

Ion exchange membranes (IEMs) are used for exchanging or removing ions from the solutions so that they are fabricated by polymers rather than metals or ceramics. When metal is in contact with the solutions, some reaction or corrosion occurs, and ceramic is difficult to use in membrane form because it is brittle. Also, normal metals and ceramics do not have high ion-exchange properties so that polymers are used widely as a host material of the IEM. The conventional IEMs are either layered membrane consisted of ion exchange material and support layer, and thick bulk membrane. There are no critical problems to use them for water treatment, but they are not suitable for electrochemical application such as reverse electrodialysis (RED). RED is a method of making electricity by sequential ion transport through semi-permeable membranes and electrochemical reaction at the electrode part so that the IEMs need to be developed for getting the structure not to interfere with ion movement through the IEM body. In the RED system, the IEMs are involved in separating ions to create the chemical potential which makes a voltage in the electrochemical system. IEMs for RED has not yet been widely adopted, and most of them are the membrane for electrodialysis (ED). Therefore, we need to study engineering approaches to improve the IEM properties.