Polymer electrolyte membrane phase separation

The required properties of solid polymer electrolyte membranes may be divided into interfacial and bulk properties [9]. As described above, the interfacial characteristics of these membrane materials are important for the optimum formation of the three-phase boundary. Hence, flow properties, gas solubility, wetting of carbon supported catalyst surfaces by the polymer, etc. are of paramount importance. The bulk properties concern proton conductivity, gas separation, and mechanical properties. This whole ensemble of properties has to be considered and balanced in the development of novel proton-exchange membranes for fuel cell application. 

Abstract Chemical structure, polymer microstructme, sequence distribution, and morphology of acid-bearing polymers are important factors in the design of polymer electrolyte membranes (PEMs) for fuel cells. The roles of ion aggregation and phase separation in vinylic- and aromatic-based polymers in proton conductivity and water transport are described. The formation, dimensions, and connectivity of ionic pathways are consistently found to play an important role in determining the physicochemical properties of PEMs. For polymers that possess low water content, phase separation and ionic channel formation significantly enhance the transport of water and protons. For membranes that contain a high... 

These types of separators consist of a solid matrix and a liquid phase, which is retained in the microporous structure by capillary forces. To be effective for batteries, the liquid in the microporous separator, which generally contains an organic phase, must be insoluble in the electrolyte, chemically stable, and still provide adequate ionic conductivity. Several types of polymers, such as polypropylene, polysulfone, polytetrafluoroethylene, and cellulose acetate, have been used for porous substrates for supported liquid membranes. The PVdF-coated polyolefin-based microporous membranes used in gel polymer lithium-ion battery fall into this category. Gel polymer electrolytes/membranes are only discussed briefly. 

Chapter 2 dwells on all aspects of the structure and functioning of polymer electrolyte membranes. The detailed treatment is limited to water-based proton conductors, as, arguably, water is nature s favorite medium for the purpose. A central concept in this chapter is the spontaneous formation of ionomer bundles. It is a linchpin between polymer physics, macromolecular self-assembly, phase separation, elasticity of ionomer walls, water sorption behavior, proton density distribution, coupled transport of protons and water, and membrane performance. 

Phase inversion operation is easier with regard to the Bellcore process. The polymer is dissolved in a mixture of a volatile solvent and a non-solvent such that the amount of the non-solvent is low enough to allow solubilization and high enough to allow phase separation upon evaporation. The resulting solution is spread as a film on a glass substrate and the solvent is allowed to evaporate at ambient temperature to form a polymer electrolyte membrane. Finally, the membrane should be allowed to swell in an electrolyte solution to produce the GPE (Stephan, 2006). 

In this section, PVA was blended with polyepichlorohydrin (PECH) in DMSO solution to prepare the PVA/PECH blend polymer membrane. The blend membrane was immersed in 6 M KOH aqueous solution to form the alkaline PVA/PECH SPE. It was improved in chemical, mechanical, and electrochemical properties [37]. The optimal blend ratio of PVA PECH was foimd to be 1 0.2. This polymer blend formed a imiform and homogeneous film. High PECH content, such as PVA PECH (1 1), resulted in phase separation morphology. The solid-state Zn/air batteries with PVA/PECH blend polymer electrolytes have been assembled and the test results are listed in Table 2. 

Solid polymer electrolytes on the basis of a polymer cation exchange membrane in H" -foim or an anion exchange polymer membrane in OH -form can be considered as quasi-aqueous electrolytes, whereby the water is absorbed in the phase separated ionic nano morphology of the respective material. This nano morphology forms imiic pathways through the polymeric membrane connecting the two fuel cell electrodes. 

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