Coatings membrane structures

Wang S, Sun G, Wang G, Zhou Z, Zhao X, Sun H, et al. Improvement of direct methanol fuel cell performance by modifying catal5fst coated membrane structure. Electrochem Commun 2005 7(10) 1007-12. 

There are two main types of thin-film catalyst layers catalyst-coated gas diffusion electrode (CCGDL), in which the CL is directly coated on a gas diffusion layer or microporous layer, and catalyst-coated membrane, in which the CL is directly coated on the proton exchange membrane. In the following sections, these catalyst layers will be further classified according to their composition and structure. 

However, we will not ignore physical properties. A section of the book will focus on structure-property relationships. PURs fonn devices that have chemical and physical features. The great value of polyurethanes as we will show in this book is the freedom to take advantage of their chemical and physical features and efficacies. While much of the book focuses on foams, we will also discuss coatings, membranes, elastomers, and their application to the problems addressed. 

In an early inaccurate model for the structure of biological membranes, a phospholipid bilayer was coated on both sides by protein in an unfolded or jS-pleated sheet conformation. This model reflected the prevailing view of membrane structure from about 1940 until the early 1970s. 

As shown in Figure 1.6, the optimized cathode and anode structures in PEMFCs include carbon paper or carbon cloth coated with a carbon-PTFE (polytetrafluoroethylene) sub-layer (or diffusion layer) and a catalyst layer containing carbon-supported catalyst and Nafion ionomer. The two electrodes are hot pressed with the Nafion membrane in between to form a membrane electrode assembly (MEA), which is the core of the PEMFC. Other methods, such as catalyst coated membranes, have also been used in the preparation of MEAs. 

Polymerized lipids do not occur in natural cell membranes. Nature tends to support fragile membrane structures with polymeric skeletons, i.e. protein cytoskeletons, polysaccharide cell walls etc. Analogous synthetic polymeric nets are simply constructed from polymerizable counterions. Negatively charged dihexadecyl phosphate vesicles can be neutralized with choline methacrylate polymerization of the latter produces a polycationic vesicle coat which is not inserted into the membrane (Figure 4.30). A cytoskeleton at the... 

In composite RO membranes, the selective top layer and the porous support layer are usually made of different polymeric materials. The selective top layer is formed on the porous support in a second step, typically by an interfacial polymerization reaction. For example, a commercially available thin film composite RO membrane is made by coating a porous polysulfone support with a polyamide thin film formed by the interfacial reaction of m-phenylenediamine and 1,3,5-benzenetricarbonyl trichloride. Details regarding membrane structures can be found elsewhere in the... 

Structure Level IV. The membrane structure of composite membranes is designated Structure Level IV in this paper. Composite membranes usually consist of a thin film of polymer on a porous substrate and are generally referred to as "thin-film composite" membranes. The coating polymer and substrate polymer are generally different polymers selected for the unique properties that each polymer component imparts to the composite membrane. 

The specific surface area of vanadium pentoxide coated membrane was 1.1 m /g, and the average pore diameter of it, measured by nitrogen adsorption, was 30A. Macro pores identified by mercury intrusion did not exist, and the porosity was approximately 9%. From results of isotherm adsortion-desorption curve,as shown in Fig.2, V2O5-coated membrane has slit-shaped pore structure. Hence the pores mostly exist between the V2O5 layers, and the surface of those are nearly non-porous. 

The X-ray diffraction reasults as a function of the heat treatment of coated membrane are shown Fig.3. The V205-coated membrane prior to calcination was an amorphous structure without any characteristic peak. When the membrane was heated to 200 °C the crystalhzation was slightly developed, and at 300 °C and 400 °C the crystallization continued to occur. But at temperature over 400 C the crystal never grew. 

Membrane electrode assemblies (MEAs) are typically five-layer structures, as shown in Figure 10.1. The membrane is located in the center of the assembly and is sandwiched by two catalyst layers. The membrane thickness can be from 25 to 50 pm and, as mentioned in Chapter 10, made of perfluorosulfonic acid (Figure 11.3). The catalyst-coated membranes are platinum on a carbon matrix that is approximately 0.4 mg of platinum per square centimeter the catalyst layer can be as thick as 25 pm [12], The carbon/graphite gas diffusion layers are around 300 pm. Opportunities exist for chemists to improve the design of the gas diffusion layer (GDF) as well as the membrane materials. The gas diffusion layer s ability to control its hydrophobic and hydrophilic characteristics is controlled by chemically treating the material. Typically, these GDFs are made by paper processing techniques [12],... 

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