Preparation of PBI/PTFE composite membranes from PBI in N,N′-dimethyl acetamide solutions with various concentrations of LiCl
ABSTRACT In this report, properties of 2 mg ml−1 PBI in N,N′-dimethyl acetamide (DMAc) solutions containing LiCl with molar ratios of [LiCl]/[BI] = 3.62–14.51 (where [BI] is the concentration of benzimidazole repeat unit in the solutions) were investigated. We show the solutions properties of PBI in DMAc mixed with LiCl (PBI/DMAc/LiCl) are strongly influenced by the molar ratio of [LiCl]/[BI] in the solutions. Thus, the properties of membranes prepared by solutions castings also depend on the LiCl concentration in the solutions. Both viscosity of PBI/DMAc/LiCl solutions and hydrodynamic radius of PBI in PBI/DMAc/LiCl solutions decrease when the molar ratio of [LiCl]/[BI] is increased from 0.0 to ∼8.0 and then increase when the molar ratio of [LiCl]/[BI] is increased from 8.0 to 14.5. These results suggest a lowest polymer aggregation of PBI in DMAc/LiCl solutions when the [LiCl]/[BI] molar is ∼8.0. Using a dialysis method with conductivity measurements, we found around 2.5 LiCl molecules were bonded on each BI repeat unit when the [LiCl]/[BI] fed molar ratio was 8.0 in PBI/DMAc/LiCl solutions. The value “2.5” of “2.5 LiCl molecules” bonded on each BI was close to the value “2” of “2 –NH groups” and “2 –NC– groups” consisted in the chemical structure of a BI repeat unit. The IR spectra also show the hydrogen bonds between –NH and –NC– of BI structures are dissociated by the presence of LiCl in PBI/DMAC solutions. These results suggest that all the –NH and –NC groups of PBI are bonded by LiCl when the [LiCl]/[BI] fed molar ratio is at ∼8.0. The porous poly(tetrafluoro ethylene) (PTFE) reinforced PBI (PBI/PTFE) composite membranes prepared from PBI/DMAc/LiCl solutions with [LiCl]/[BI] molar ratios of 3.6, 8.0, and 9.0 were used to prepare membrane electrode assemblies (MEA). The fuel cells performances of these MEAs were investigated at 150 °C and revealed a highest fuel cell performance when the composite membrane was prepared from a solution with a [LiCl]/[BI] molar ratio of ∼8.0.
- International Journal of Hydrogen Energy 10/2013; 38(31):13742-13753. · 2.93 Impact Factor
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ABSTRACT: A novel way for anion exchange membrane (AEM) preparation has been investigated, avoiding the use of expensive and toxic chemicals. This new synthetic approach to prepare AEMs was based on the use of a porous polybenzylimidazole membrane as support in which functionalized ILs were introduced and subsequently grafted on the polymer backbone. These new AEMs were prepared and their chemical structures and properties including morphology, thermal stability, and ionic conductivity were characterized. The hydroxyl ionic conductivity of the synthesized membranes can reach values upto 6.62 × 10−3 S cm−1 at 20°C. Although the ionic conductivity is not very high yet, the work shows the strength of the concept. Membrane properties can be easily tailored toward specific applications by choosing the proper chemistry, i.e., porous polymer support, ionic liquid, and method of initiation and polymerization. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013Journal of Applied Polymer Science 08/2013; 129(3). · 1.40 Impact Factor
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ABSTRACT: In this work we propose the use of the ionic liquid 1-H-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([h-mim] Ntf2) as conductive filler in a tailor-made porous, polymeric polybenzimidazole (PBI) support as proton conductive membrane for high temperature (>100 °C) fuel cell applications. PBI is chosen because of its excellent thermal and mechanical stability, while the choice for the ionic liquid is based on its high proton conductivity, low water sorption, thermal stability and low viscosity.The morphology of the porous PBI support is especially tailored for this application using a delayed immersion precipitation process. The macrovoid free porous structure has a volume porosity of 65% and a pore size of approximately 0.5 μm.Pores filling with ionic liquid by direct immersion of the PBI support into molten ionic liquid at 50 °C introduced the membrane proton conductivity. After impregnation the proton conductivity of this PBI/IL membrane reached a value of 1.86 mS cm−1 at 190 °C. Fuel cell performance of these membranes clearly exceeds that of Nafion 117 at temperatures above 90 °C. A power density of 0.039 W cm−2 is obtained at the intended operation temperature of 150 °C, which proofs that the developed PBI/IL membrane can be considered as a serious candidate for high temperature fuel cell applications.Journal of Power Sources 01/2013; 222:202–209. · 5.21 Impact Factor