Phosphoric acid-impregnated membrane

Asensio, J.A., Borros, S., and Gomez-Romero, R, Polymer electrolyte fuel cells based on phosphoric acid-impregnated poly(2,5-benzimidazole) membranes, J. Electrochem. Soc., 151, A304, 2004. 

Wannek C, Lehnert W, Mergel J (2009) Membrane electrode assemblies for high-temperature polymer electrolyte fuel cells based on poly (2,5-benzimidazole) membranes with phosphoric acid impregnation via the catalyst layer. J Power Sources 192 258-266... 

Asensio J A, Borros S and Go mez-Romeroa Pet al. (2004) Polymer Electrolyte Fuel Cells Based on Phosphoric Acid-Impregnated Poly-2,5-benzimidazole Membranes, J. Electrochem. Soc., 151, pp. A304-A310... 

Asencio JA, Borr6s S, G6mez-Romero P (2004) Sulfonated poly(2,5-benzimidazole) (SABPBI) impregnated with phosphoric acid as proton conducting membranes for polymer electrolyte fuel cells. Electrochim Acta 49 4461-4466... 

The state of the art of PBI-based polymer electrolyte membranes for their use in high-temperature fuel cells working at 150-200 °C has been reviewed [28]. Several PBI copolymers and related compounds have been investigated for this application. Besides phosphoric acid, many other strong inorganic acids have been used for impregnation. 

Phosphoric acid-doped polybenzimidazole (PA-PBl) membrane is the most common type for HT-PEMFCs. It was also introduced in the catalyst layer as an ionomer to improve proton conductivity [8, 80-83]. Similar to die apphcation of Nafion ionomer in the catalyst layer, polybenzimidazole (PBl) solution was incorporated into the catalyst layer by an impregnation method (die electrode was soaked in a PBI solution), by a gluing method (the PBl membrane was coated by PBI solution), or by a brushing method (the PBl solution was brushed onto the electrode) [80]. 

In PAFCs the protic electrol3d e phosphoric acid is impregnated in a porous separator, e.g. silicon carbide. Thus, considerable amounts of free (highly concentrated) phosphoric acid are present in the cell, which can be a safety issue for certain applications. In case of HT-PEMFCs the protic electrolyte phosphoric acid is adsorbed in a temperature-resistant polybenzimidazole-t) e (PBI) polymer membrane. 

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