Requirements of High-Performance Membranes

The success of an electrochemical process can depend critically on the selection of the proper membrane. Yet, general criteria by which a membrane can be selected do not exist. The essential properties of the membrane for electrochemical applications include good permselectivity, high ionic conductivity, no electronic conductivity, adequate chemical and thermal stability, and sufficient mechanical strength under operating conditions. 

The membrane is a compromise of properties the requirement for low internal resistance suggests that the membrane be porous and thin good separation dictates that the membrane be of low permeability and high fixed charge concentration and adequate physical strength requires that it be sufficiently thick. At any rate, membranes can generally be tailor-made, so that their properties can be adjusted to yield optimal cell performance and cell life.  

The interest in perfluorinated ion-exchange membranes has increased extensively in recent years because of their industrial importance. A growing body of research concerning their structure and properties has developed. Much of this work has been summarized in a recent monograph. While perfluorinated anion-exchange membranes have not yet been produced, several perfluorinated cation-exchange types have been synthesized and fabricated into membrane form, as listed in Table 1. 

The perfluorinated sulfonate (Nafion) polymer was synthesized and developed by du Pont about 17 years It was 

Perfluorinated carboxylate membranes were introduced about seven years ago. These membranes can be synthesized by a variety of methods or by various chemical conversions from the Nafion polymer.Composite membranes which contain both sulfonate and carboxylate functional groups have also been produced (see Section IV.l for more details). These carboxylate membranes have been widely employed in the advanced membrane chlor-alkali cells. This major chemical technology is in the process of being revolutionized by the use of these materials, a remarkable accomplishment for such a small group of polymers.  

---