Polymer electrolyte membrane structure formation

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... 

In a fuel cell, the membrane is sandwiched between two bipolar plates. This structure puts it under compressive stress, which can change the membrane resistance. It has been found that the resistance of Nafion membranes increased when they were compressed, and the increase was consistent with the elastic compression of the membrane (Satterfield et al, 2006). Casciola et al. (2006) also found that membrane conductivity decay occurs only when the membrane is forced to swell anisotropically along the plane parallel to the membrane surface. In addition to the effect of compression on conductivity decay, polymer membranes in fuel cells undergo creep, which can cause membrane thinning, pinhole formation, and other failure. Stuck et al. (1998) proposed that local stress most likely triggered and/or enhanced the nonuniform thinning of the Nafion membranes in a polymer electrolyte membrane electrolyzer. 

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. 

In comparison with the FBI membranes cast from organic solvents and subsequently imbibed with phosphoric acid, the PA-doped FBI polymer electrolyte membranes prepared via the PPA process possessed high PA loading levels with good mechanical properties and enhanced proton conductivities. It was shown that the polymer molecular structures significantly affected the properties of the polymers and the corresponding film formation process. In addition to... 

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