Partially fluorinated aarylene polyethers and their ternary blends with PBI and H3PO4.: Part II.: Characterisation and fuel cell tests of the ternary membranes

Ternary blend membranes based on sulphonated partially fluorinated arylene polyether, polybenzimidazole (PBI) and phosphoric acid were prepared and characterised as electrolyte for high temperature proton exchange membrane fuel cells. Partially fluorinated arylene polyether was first prepared from polycondensation of decafluorobiphenyl with 2,2-bis(4-hydroxyphenyl)hexafluoropropane, followed by sulphonation with H2SO4/60% SO3, based on which binary blends with PBI were prepared and further doped with concentrated phosphoric acid at temperatures of up to 130 degrees C, Acid doping levels as high as 10-13 mol phosphoric acid per PBI repeat unit can be reached, showing small swelling and excellent mechanical strength. At an acid doping level of 11, a conductivity of 0.12 S cm(-1) was obtained at 175 degrees C and 10% relative humidity. Such a membrane exhibits a tensile strength of 6 MPa, elongation of 220% and modulus of 50 MPa at 150 degrees C. Based on these ternary membranes large MEAs with an active area of 256 cm(2) have been prepared for a 2 kW(el) stack showing good performance and reproducibility.