| Perfluorinated membranes like Nafion, has been widely used in fuel cells. However, this type of film is still facing many problems, such as high humidity-dependent, high methanol permeability and high cost. Therefore, the search for alternatives to Perfluorinated membranes has remained a large branch of fuel cell science over the past few decades. In fact, the ion exchange membrane has some basic performance requirements like high conductivity, low permeability, high chemical stability and excellent mechanical properties. Currently, ion-exchange membranes can be divided into two types-proton exchange membranes and anion exchange membranes. This paper will study on the two type of ion-exchange membranes, by synthesising of several novel ion exchange membranes, and discussing its performance in fuel cell applications.In chapter 2, a series of naphthalenic copolyimides have been prepared by random copolymerization of ODADS,BAPBDS,BAPF,ODA and BSPOB with NTDA. To improve the mechanical stability, the membranes were cross-linked through the reaction of sulfonic acid groups with hydrogen atoms of activated phenyl groups located in neighboring chains using appropriate catalyst. Focused on the relationship between the activity of the cross-linking reaction and the polymer structure, experimental results showed that the reactivity of sulfonic acid groups varies in the following order:SPI51>>SPIB41> =SPIO31. This suggested that the sulfonic acid group with no substituent in its ortho postion, apart from the main polymer chains and attaching to activated benzene rings, was highly reactive. The IEC of the membranes were higher than 2.0 and the number of molecules of water per ion-exchange group lied in the vicinity of 20. The conductivity of the MEAs at 75℃was of the order of 10-2 S/cm and the power of the cell was 225Mw/cm2. The polarization curves obtained for the MEAs were similar to those of Nafion 112 MEAs. The good chemical and mechanical stabilities of the cross-linked naphthalenic copolyimide membranes make them candidates as solid electrolytes for fuel cells. In chapter 3, a series of anion exchange membrane with different IEC was synthesized by the reaction between new PBI with pendant amino group and 4-methyl-4-glycidylmorpholin-4-ium chloride. These new PBI based anion exchange membranes showed very good alkali resistance. By soaking in 60℃,6mol/L NaOH solution for 7 days, no significant loss of mechanical strength was found. All membranes were cross-linked by epoxy resin E51 to control the swelling ratio. The cross-linked membranes showed good mechanical properties. The max.stress was 45MPa for OHPBI-1/2 at 50%RH. The conductivity of OHPBI-1/2 in DI water at 80℃was of the order of 5×10-2s/cm. The good chemical and mechanical stabilities of the cross-linked OHPBI anion exchange membrane showed a good future in fuel cell application.
|
PDF Full Text Request