Composite membranes of polybenzimidazole and caesium-salts-of-heteropolyacids for intermediate temperature fuel cells

Inorganic-organic composite electrolyte membranes were fabricated from Cs substituted heteropolyacids (CsHPAs) and polybenzimidazole (PBI) for application in intermediate temperature hydrogen fuel cells. Four caesium salts of heteropolyacid, (Cs(X)H(3-X)PMo(12)O(40) (CsPOMo), Cs(X)H(3-X)PW(12)O(40) (CsPOW), Cs(X)H(4-X)SiMo(12)O(40) (CsSiOMo) and Cs(X)H(4-X)SiW(12)O(40) (CsSiOW)), were used to form composite membranes with PBI. The membranes were characterized by using SEM, FTIR and XRD. The CsHPA powders were nano-sized as shown in the XRD and SEM data. The CsHPA/PBI composite membranes loaded with H(3)PO(4) had high conductivity, greater than that of a phosphoric acid loaded PBI membrane. The conductivity increased with an increase in the percentage of the powder in the composite. The 30% CsPOMo/PBI/H(3)PO(4) exhibited a conductivity of 0.12 S cm(-1) under anhydrous conditions, although its mechanical strength was the poorest, but still promising with a value 40 MPa. The performance of the hydrogen fuel cell with composite membranes was better than that with a phosphoric acid-doped PBI membrane under the same conditions. The CsPOMo gave the best power density of around 0.6 W cm(-2) with oxygen at atmospheric pressure.