Membranes, catalyst-coated

Membrane Reactor. Another area of current activity uses membranes in ethane dehydrogenation to shift the ethane to ethylene equiUbrium. The use of membranes is not new, and has been used in many separation processes. However, these membranes, which are mostly biomembranes, are not suitable for dehydrogenation reactions that require high temperatures. Technology has improved to produce ceramic and other inorganic (90) membranes that can be used at high temperatures (600°C and above). In addition, the suitable catalysts can be coated without blocking the pores of the membrane. Therefore, catalyst-coated membranes can be used for reaction and separation. 

M. K. Debe. Novel catalysts, catalyst supports and catalyst coated membrane methods. In Handbook of fuel cells Fundamentals, technology and applications. Vol. 3 Fuel cell technology and applications, ed. W. Vielstich, H. A. Gasteiger, and A. Lamm, 576 (2003). New York John Wiley Sons. 

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. 

Catalyst layer ink can be deposited on gas diffusion layers to form a CCGDL, as discussed in the previous section. Alternatively, the catalyst ink can be applied directly onto the proton exchange membrane to form a catalyst-coated membrane (CCM). The most obvious advantage of the CCM is better contact between the CL and the membrane, which can improve the ionic connection and produce a nonporous substrate, resulting in less isolated catalysts. The CCM can be classified simply as a conventional CCM or as a nanostructured thin-film CCM. 

The nanostructured thin-film electrode was first developed at 3M Company by Debe et al. [40] and Debe [41], who prepared thin films of oriented crystalline organic whiskers on which Ft had been deposited. The film was then transferred to the membrane surface using a decal method, and a nanostructured thin-film catalyst-coated membrane was formed as shown in Figure 2.10. Interestingly, both the nanostructured thin-film (NSTF) catalyst and the CL are nonconventional. The latter contains no carbon or additional ionomer and is 20-30 times thinner than the conventional dispersed Pt/ carbon-based CL. In addition, the CL was more durable than conventional CCMs made from Pt/C and Nation ionomer [40]. 

Dry the catalyst-coated membrane in a vacuum at a temperature of approximafely 160°C. 

The hybrid sulphur process requires electrolysers which are not described in chemical engineering economics literature. A specific approach has been developed by collecting data from literature and constructors of alkaline electrolysers (Mansilla, 2008). Electrolyser characteristics are also considered (catalyst coating, membranes). 

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. 

Debe, M., Novel catalysts, catalysts support and catalysts coated membrane methods, in Elandbook of Fuel Cells Fundamentals, Technology, and Applications, 1st ed., Vielstich, W., Lamm, A., and Gasteiger, H.A., Eds., John Wiley Sons, West Sussex, England, 2003, p. 576. 

Li, N., Assmann,)., Schuhmann, W., and Muhler, M. (2007) Spatially resolved characterization of catalyst-coated membranes by distance-controlled scanning mass spectrometry utilizing catalytic methanol oxidation as gas-solid probe reaction. Analytical Chemistry, 79 (15), 5674-5681. 

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],... 

Define pilot manufacturing scale-up of the processes for fabrication of catalysts, catalyst coated membrane (CCM) assemblies, and electrode backing media. 

Phase 2 Laboratory-scale catalyst-coated membranes (CCMs) will be fabricated, optimized and tested using the Phase 1 down-selected membranes and catalysts. 

Debe M (2003) Novel Catalysts, Catalyst Supports and Catalysts Coated Membrane Methods. In Vielstich W, Gasteiger HA, Lamm A (eds) Handbook of Fuel Cells -Fimdamentals, Technology and Application, Part 3. John Wiley Sons, Chichester, p 576... 

Fig. 14.1 Functional layers in a fuel cell. Functional layers can be integrated to a component such as catalyst coated membrane (CCM), catalyst coated substrate (CCS)/gas diffusion electrode (GDE) or bipolar plate (BPP)...

Individual layers can be integrated to components such as the electrolyte membrane and the two catalyst layers to a Catalyst Coated Membrane (CCM). Another option is the integration of the gas diffusion layer and the catalyst layer to a Gas Diffusion Electrode (GDE). The gas functions of distribution, gas separation and coolant distribution are commonly integrated into the BiPolar Plate (BPP). 

Fig. 14.3 MEA-configurations (a) catalyst coated membrane (CCM, 3-layer MEA), (b) CCM with gasketing frame (5-layer MEA), (c) 5-layer MEA with gas diffusion layers attached (7-layer MEA)...

Catalyst Coated Membrane (CCM) or three-layer MEA, consisting of the polymer electrolyte coated by a catalyst layer on either side. 

Fig. 14.11 Cross-section of a degraded catalyst coated membrane [58]...

In the preparation of MEA, there are two options. One is to coat the CL onto the DM such as carbon paper, or carbon cloth, the other is to coat the CL onto the PEM, as shown in Figure 3.17. The CL coated on the diffusion medium is called Catalyst-coated Diffusion Medium (CDM), and the CL coated on the membrane is called Catalyst Coated Membrane (CCM). Using a hot-press process, by sandwiching PEM between two CDMs, or CCM between two DMs, an MEA can be fabricated for fuel cell testing. 

The standard PEMFC is built up in a sandwich-like manner with the membrane as a mirror plane. The proton-conducting membrane is at the core of the device, covered on both sides by the catalytically active porous electrodes, next to them GDLs for fine gas distribution, heat and water management, and flow fields for the coarse distribution of the feeds. The electrodes can then be bound to either the membrane (so-called catalyst-coated membrane = CCM) or the GDL (so-called gas diffusion electrode = GDE). 

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