approximately the last ten years. The major focus of the first part of the chapter is on three main systems: (1) the well-developed meta-PBI (poly(2,2-m-phenylene-5,5 - bibenzimidazole)); (2) the various derivatives and filled systems based on meta-PBI; and (3) poly(2,5-benzimidazole) (AB-PBI). The polymer membrane properties, such as thermal and chemical stability, ionic conductivity, mechanical properties, and ability to be manufactured into a membrane and electrode assembly (MEA), are discussed in detail. Preliminary fuel cell performance is reported for a number of PBI chemistries. The second section of the chapter highlights recent work on developing a novel process to produce phosphoric acid (PA)-doped PBI membranes for use in high-temperature PEMFCs. This novel sol-gel process, termed the polyphosphoric acid (PPA) process, allows production of a gel membrane that exhibits properties not observed with the “traditionally” prepared PBIs, such as improved ionic conductivity, mechanical properties, fuel cell performance, and long-term stability. The final section of the chapter focuses on the possible degradation modes of the commercially available products from BASF Fuel Cells.
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