Porosity carbon fiber felt

Carbon fiber or graphite fiber materials, available, for example, as felt, clothes, or paper, and so on, are state of the art for realizing conductive diffusion zones in fuel cells but also they can be used as electrodes. They attain a very high porosity (free space volume up to 80%) and a surprisingly good elasticity. 

FIBROUS ACTIVATED CARBON is an ACTIVATED CARBON in the form of fibers, filaments, yarns or rovings and fabrics or felts. Such fibers differ from CARBON FIBERS, used for reinforcement purposes in composites, in their high surface area, high porosity and low... 

A well-qualified substrate layer should have excellent gas permeability, high electron conductivity, smooth surface, good mechanical strength, proper wettability, stable chemical and heat properties, as well as low cost. The most common SL materials used in PEMFCs are carbon-fiber-based products, such as non-woven carbon papers and woven carbon cloths. This is mainly due to their high porosity (> 70%) and good electrical conductivity. Besides these carbon materials, some metal substrates such as sintered porous titanium and stainless steel fiber felt have also been explored as SLs [12-14] because of their high mechanical strength, ductility, and low cost. 

Carbon electrodes are commercially available in many forms. These include plates, foams, felts, cloths, fibers, spherical and other particles suitable for beds or powders. Graphite or amorphous carbons exhibit quite different performances. Porosity, surface area and pretreatment are important variables to be considered in designing carbon electrodes. 

The GDL of PEM fuel cells connects between the bipolar plate/flow channel and catalyst layer. It provides the pathways for mass, heat, and electron transport, and also acts as the physical support of CL and membrane. The present state-of-the-art GDL consists of both a macroporous substrate and a micropo-rous layer (MPL). The macroporous substrate is a porous network of graphite fibers, which is usually carbon paper, carbon felt or carbon cloth. The substrate is often coated with hydrophobic materials such as PTFE for better liquid water removal. The MPL is coated on one side of the substrate which faces the catalyst layer. A typical MPL is a composite layer mixed by carbon particles and PTFE. The MPL usually has lower porosity and permeability but higher hydrophobicity and electrical/thermal conductivity than its substrate layer. The MPL enhances the water management and thermal/electricity connection between the substrate layer and CL to better cell performance. Unlike the membrane and catalyst layer, researches focusing on developing new materials and/or revolutionary design are scarce. Therefore, this subsection only focuses on the macroporous substrate/MPL GDL. 

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