Teflon®-bonded silicon carbide

Phosphoric acid fuel cells (PAFC) use liquid phosphoric acid as an electrolyte - the acid is contained in a Teflon-bonded silicon carbide matrix - and porous carbon electrodes containing a platinum catalyst. The PAFC is considered the "first generation" of modern fuel cells. It is one of the most mature cell types, the first to be used commercially, and features the most proven track record in terms of commercial applications with over 200 units currently in use. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses. 

The catalysts and electrode materials used in PAFCs are also similar to those in acidic H2/air fuel cells. Carbon-supported Pt is used as the catalyst at both anode and cathode, porous carbon paper serves as the electrode substrate, and graphite carbon forms the bipolar plates. Since a liquid electrolyte is used, an efficient water removal system is extremely important. Otherwise, the liquid electrolyte is easily lost with the removed water. An electrolyte matrix is needed to support the liquid phosphoric acid. In general, a Teflon -bonded silicon carbide is used as the matrix. 

Classical phosphoric add fuel cells use phosphoric add as the electrolyte, which is immobilized in a Teflon bonded silicon carbide matrix. Phosphoric acid fuel cells usually work at temperatures around 200 °C and are able to tolerate carbon monoxide levels of up to 2 vol.% [1]. Platinum/ruthenium as the anode catalyst may improve the performance in presence of carbon monoxide, similar to PEM fuel cells [33]. 

Polymers are nsed in fnel cells. Those of particular interest are the polymer electrolyte membrane (PEM) and the phosphoric acid fuel cell (PAFC) designs. The latter design contains the liquid phosphoric acid in a Teflon bonded silicon carbide matrix. In March 2005 Ticona reported that it had bnilt the first fnel cell prototype made solely with engineering thermoplastics. They claimed that this approach rednced the cost of the fuel by at least 50% when compared with fuel cells fabricated from other materials. The 17-cell unit contains injection moulded bipolar plates of Vectra liquid crystal polymer and end plates of Fortron polyphenylene sulfide (PPS). These two materials remain dimensionally stable at temperatures up to 200 "C. The Vectra LCP bipolar plates contain 85% powdered carbon and are made in a cycle time of 30 seconds. 

From the point of view of polymer usage the types of particular interest are the PEM and the phosphoric acid PAFC designs. The latter design contains the liquid phosphoric acid in a Teflon bonded silicon carbide matrix. 

Composite Plating. An electroless nickel matrix can be used to securely bond diamonds to cutting tools, and electroless nickel—diamond composites are also used (see Tool materials). The NYE-CARB process gives a silicon carbide—electroless nickel composite that has extremely high abrasion resistance (49). Electroless nickel—Teflon composites are being promoted as low friction materials. 

---