PBIs high temperature tolerance

The earliest work describing a PBI/PA complex for fuel cell use was reported by Wainright et al. in 1995 [2]. This research detailed various synthesis methods and characterization of the resulting polymer, and was further reviewed by Kim and Lim [3]. Because PBI is thermally stable [4-7], mechanically robust, chemically stable, and exhibits high CO tolerance [8], it was shown to be a promising high-temperature fuel cell membrane candidate. Since its introduction, the majority of research has focused on increasing the... 

BASF Fuel Cells (formerly PEMEAS or Celanese Ventures) produces polybenzimidazole (PBI)-based high-temperature membrane and electrode assemblies sold under the brand name Celtec . These MEAs operate at temperatures between 120 °C and 180 °C. One of the distinct advantages of high-temperature PEMFCs is exhibited in their high tolerance toward fuel gas impurities, such as CO (up to 3%), H2S (up to 10 ppm), NH3, or methanol (up to several percent), compared to low-temperature PEMFCs. Additionally, waste heat can be effectively used and, therefore, the overall system efficiency is increased. 

PBI membranes have been the critical components in high temperature polymeric electrolyte membrane fuel cells. PBI fuel cells tolerate much more impurities in the Hj fuel compared to low temperature fuel cells. Therefore, they are preferred in fuel cell systems where the Hj supplies are from reformers converting other fuels to Hj. PBI fuel cells are also suitable for combined heat and power fuel cell systems. In other applications, PBI membranes have been successfully demonstrated to purify Hj while pumping it against a high pressure. The technology can be applied... 

The proton conduction based on the phosphoric acid is the basis of HT-PEMFC Celanese technology [37], mostly referred to as phosphoric acid-doped PBI (polybenzimidazole) This membrane enables operation at temperatures as high as 180°C, without the need for external humidification. Heat dissipation at this temperature is much easier than at the 70-80°C operating temperature of fuel cell systems using standard PFSA membranes. The CO tolerance at 180°C is such that even 1 % CO leads to a minor loss of power density compared to that using the same membrane on pure hydrogen. The downside of this membrane is its low conductivity below 1(X)°C, making a cold start impossible, as well as the lower power density at its optimal temperature. 

High working temperatures benefit PEMFC performances because of faster electrode kinetics, higher CO tolerance and the possibility to use the residual heat for energy cogeneration [5, 6]. Among the polybenzimidazole derivatives, the most widely studied are the commercially available poly[2,2 -(m-phenylene)-5,5 -bibenzimidazole] with the acronyms w-PBI and poly(2,5-benzimidazole), AB-PBI (see Fig. 8.1). The polymers contain a basic imidazole functionality that allows the uptake of the acid protic electrolyte, which is responsible, and required, for the proton... 

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