Novel anti-oxidative membranes based on sulfide-containing polybenzimidazole for high temperature proton exchange membrane fuel cells

Abstract

The introduction of sulfide units is a potential strategy to improve solubility and processibility of polybenzimidazole (PBI) polymer, as well as to enhance antioxidant capacity of corresponding membrane. In this paper, the novel S-PBI-x serial copolymers (x denotes the percentage of sulfide-containing monomer) were prepared by a microwave-assisted tetracopolymerization with 3,3′,4,4′-tetraaminobiphenyl, 2,6-pyridinedicarboxylic acid, hexanedioic acid and the synthesized methyl 3-((2-methoxy-2-oxoethyl)thio)propanoate as copolymerized monomers in different proportion. The resultant copolymers were characterized by FT-IR, GPC and energy dispersive spectroscopy. These sulfide-containing copolymers exhibit much better solubility in aprotic solvents such as N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide than unmodified PBI. The oxidative stability of the membranes was studied by enhanced Fenton test (20% H2O2 and 4 ppm Fe2+, 80 °C, refreshed every 3 h). Additionally, the oxidized membranes were further characterized by FT-IR, TGA, and tension test. The experimental results show that S-PBI-7% membrane suffers less than 5% weight loss after 24 h of treatment with enhanced Fenton reagent. Typically, after treated in enhanced Fenton reagent, the oxidized S-PBI-7% membrane still retains considerable thermal stability and mechanical strength. The anti-oxidative mechanism of the prepared membranes was discussed as well.