Proton-conducting membranes based on poly(2,5-benzimidazole) (ABPBI) and phosphoric acid prepared by direct acid casting

We report the preparation of phosphoric acid doped poly (2,5-benzimidazole) (ABPBI) membranes for PEMFC by simultaneously doping and casting from a poly(2,5-benzimidazole)/phosphoric acid/methanesulfonic acid (MSA) solution. The evaporation of MSA yields a very homogeneous membrane having a better controlled composition, avoiding the use of solvent-intensive procedures. Membranes have been prepared with contents of up to 3.0H(3)PO(4) molecules per ABPBI repeating unit. These membranes achieve a maximum conductivity of 1.5 x 10(-2) S cm(-1) at temperatures as high as 180degreesC in dry conditions. These ABPBI membranes are more conveniently prepared than those conventionally formed and doped in separate steps while featuring comparable conductivities (ABPBI x 2.7H(3)PO(4) prepared by the soaking method showed a conductivity of 2.5 x 10(-2) S cm(-1) at 180degreesC in dry conditions). (C) 2004 Elsevier B.V. All rights reserved.