Carbon cloth fabrication

Among nonmetallic materials, glass, chemical stoneware, enameled steel, acid-proof brick, carbon, graphite, and wood are resistant to iodine and its solutions under suitable conditions, but carbon and graphite may be subject to attack. Polytetrafluoroethylene withstands Hquid iodine and its vapor up to 200°C although it discolors. Cloth fabrics made of Saran, a vinyHdene chloride polymer, have lasted for several years when used in the filtration of iodine recovered from oil-weU brines (64). 

As discussed previously, a number of different materials have been considered as potential candidates to be used as diffusion layers in PEMFCs and direct liquid fuel cells (DLFCs). The two materials used the most so far in fuel cell research and products are carbon fiber papers and carbon cloths, also known as carbon woven fabrics. Both materials are made from carbon fibers. Although these materials have been quite popular for fuel cells, they have a number of drawbacks—particularly with respect to their design and model complexity—that have led to the study of other possible materials. The following sections discuss in detail the main materials that have been used as diffusion layers, providing an insight into how these materials are fabricated and how they affect fuel cell performance. 

Along with CFPs, carbon cloths have also been widely used materials for diffusion layers in fuel cells. Figure 4.6 shows SEM pictures of typical carbon cloth materials used in fuel cells. The majority of these fabrics are made from PAN fibers that are twisted together in rolls. For details regarding how normal PAN fibers and carbon fibers are fabricated, please refer to Section 4.2.I.I. In this section, we will briefly discuss the fabrication process of carbon cloths. 

This same study also determined that the weaving process used to fabricate the carbon cloths plays an important role in the final thickness of the material. 

Another important point regarding the fabrication process of MPLs is that, typically, when carbon fiber paper is used as the DL, the MPL is coated on only one surface of the CFP. However, when a carbon cloth DL is used, it is normally coated on both sides with MPLs. Section 4.3.S.4 will discuss these DLs with multiple microporous layers in more detail. 

Another important point regarding the fabrication process of MPLs is the fact that, typically, when carbon fiber paper is used as the DL, the MPL is coated just on one surface of the CLP. However, when a carbon cloth is used, a homogeneous water suspension of carbon powder and PTFE is filtered under vacuum onto both faces of the carbon cloth material to form the MPLs [153,158,161,171], followed by drying and sintering as mentioned earlier. Antolini et al. [161] were able to demonstrate that carbon cloth with double MPLs, for both the anode and the cathode sides, showed better performance than when a CFP was used as the cathode DL with one MPL. At low current densities, the difference between the two DLs was not as obvious, but it became more evident at higher current densities because the limiting current densities for each case are quite different ( 1.6 A cm for CFP vs. 2.7 A cm for CC) (see Figure 4.20 for more details). 

Dual Laminate (Fluoropolymer-lined FRP) Same as Adhesive-bonded Fabricate liner first on a mandrel (hand and machine welding) and build FRP laminate over the liner. Use carbon cloth for spark testing Shop and Field Pressure OK (RTP-1 Dual lam) Vacuum OK for FRP/fluoropolymer bond. Design FRP for vacuum 33 dia max Visual Spark AE CRBBD Possible Testing recommended... 

The cylindrical section of the vessel is fabricated using fusion welding followed by carbon cloth and FRP laminating. 

The forced flow-thermal gradient CVI process (FCVI) has been shown to permit the rapid consolidation of SiC matrix composites. Recently, the FCVI process has been extended to the fabrication of carbon fiber-carbon matrix composites. Using 2D carbon cloth preforms, composite disks 0.8 cm thick have been fabricated in less than three hours a small fraction of the time required for either the resin/pitch or conventional CVI processing. Further, the FCVI process facilitates the incorporation of oxidation inhibitors within the carbon matrix and may permit obtaining a preferred crystallographic orientation that yields the high thermal conductivity required for thermal management applications. 

PANI-NTs synthesized by a template method on commercial carbon cloth have been used as the catalyst support for Pt particles for the electro-oxidation of methanol [501]. The Pt-incorporated PANl-NT electrode exhibited excellent catalytic activity and stabUity compared to 20 wt% Pt supported on VulcanXC 72R carbon and Pt supported on a conventional PANI electrode. The electrode fabrication used in this investigation is particularly attractive to adopt in solid polymer electrolyte-based fuel cells, which arc usually operated under methanol or hydrogen. The higher thermal stabUity of y-Mn02 nanoparticles-coated PANI-NFs on carbon electrodes and their activity in formic acid oxidation pomits the realization of Pt-free anodes for formic acid fuel cells [260]. The exceUent electrocatalytic activity of Pd/ PANI-NFs film has recently been confirmed in the electro-oxidation reactions of formic acid in acidic media, and ethanol/methanol in alkaline medium, making it a potential candidate for direct fuel cells in both acidic and alkaline media [502]. 

A Spectracarb 2225 carbon fabric (Engineered Fibres Technologies) was used as a basis for the synthesis of an AQ-modified carbon cloth (C-AQ) electrode. This cloth was immersed into the salt of anthraquinone-1-diazonium chloride 0.5 ZnCl2 in acetone. Then, water and 50 wt% hypophosphorous acid were added. Then, the thus-modified cloth was washed by deionized water and dried at 110°C for 20 min. 

In another attempt for fabrication of an enz5mie-based biosensor, glucose oxidase (GOD) was immobilized in PEDOT-PSS pol5mier deposited on carbon cloth (CCl) substrate modified with... 

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. 

Wiegmann et al. ° have also extended the reconstraction formalism for woven microstructure generation. The reconstraction technique creates a 3D realization of a woven GDL based on structural inputs such as weave diagram, thread width, thread height and thread pitch. The inner structure of the multifilament threads is created using the number of filaments (i.e. carbon fibers), their diameter and waviness. The input parameters canbe obtained from the fabrication specifications, e.g. fi om the sample SEM micrographs or CT scans. Figure 9.8 shows a representative 3D reconstructed woven carbon cloth GDL microstracture. 

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