Phosphoric acid doped ab-PBI membranes and its applications in high temperature PEMFC

Poly (2,5-benzimidazole) (ab-PBI) was prepared from 3,4-diaminobenzoic acid via a polymerization reaction. The obtained polymer exhibits an excellent thermal stability at temperatures up to 500 degrees C. The membranes of ab-PBI are readily to be doped with phosphoric acid at room temperature. The acid doped ab-PBI membranes present proton conductivity in a level of 10(-2)-10(-1) S/cm at temperatures above 100 degrees C. The conductivity of the acid doped ab-PBI membranes was studied in a temperature range of 80 to 200 T under different relative humidities and with different acid doping levels. Proton exchange membrane fuel cell(PEMFC) test results indicated that about 200 mW/cm(2) of power density was obtained with phosphoric acid doped ab-PBI as the electrolyte under atmospheric pressure at 200 degrees C and without humidification.