Preparation And Characterization Of Polybenzimidazole Based Composite Membranes

Proton exchange membrane (PEM) is one of the key components of proton exchange membrane fuel cells (PEMFC), which plays the critical role of separating the anode and cathode side of PEMFC and transferring the proton, etc. Currently, the widely used PEMs are perfluorosulfonic acid membranes (such as Nafion) have some shortcomings which are stillbarriers of PEMFC against successful commercialization such as their high methanol penetrating coefficient and low conductivity at high temperature. In order to overcome these deficiencies, polybenzimidazole was chosen as the base polymer and modified by chemical methods to prepare acid-base and porous-PTFE reinforced composite membranes. Cross-linked network structure was formed by the ionic bond between the acid and base groups in the acid-base polymer blend membranes, which increased the resistance of the methanol penetrating and dimensional stability properties for DMFC applications. Porous-PTFE reinforced composite membranes were prepared by fixing polybenzimidazole in the pores of PTFE to ensure the high mechanical strength and dimensional stability when the phosphoric acid doping level was high, for high-temperature proton membrane fuel cells.1.3,3',4,4'-amino-diphenyl ether was successfully synthesized and characterized by'H-NMR and FTIR. Then a series of diphenyl ether based sulfonated polybenzimidazoles (SPBI) were prepared by direct polycondensation from 5-sulfo isophthalate sodium, isophthalic acid and 3,3',4,4'-amino-diphenyl ether, the structure of which was confirmed by FTIR. The experimental results demonstrated that sulfonated polybenzimidazoles have high solubility, good thermal stability, low water uptake as well as good resistance to oxidation, indicting potential prospect of applications.2. Acid-base composite membranes derived from sulfonated polybenzimidazole (SPBI) and sulfonated poly(arylene ether sulfone) were prepared via solution blend process. Properties of the membranes were characterized in terms of swelling ratio in methanol aqueous solution, water uptake, methanol permeability coefficient and proton conductivity. The experimental results indicated that the introduction of SPBI reduced the methanol swelling and methanol permeability coefficient of the membranes. Although the proton conductivity decreased with the addition of SPBI, the composite membrane showed a relatively high proton conductivity with certain SPBI content at high temperature. Thus, the composite membranes could be used as proton exchange membranes for direct methanol fuel cell applications.3. SPBI/PTFE composite membranes were prepared by impregnating SPBI resin into porous PTFE substrate membrane which was pre-treated by surface modification. The microstructures of composite membranes were studied by SEM. The results indicated that SPBI resin was well plugged into the micropores of PTFE. The proton conductivity, dimensional stability and mechanical strength of the composite membranes were apparently improved. Thus, the composite membranes could be used as proton exchange membranes for high temperature proton exchange membrane fuel cell applications.