Pore size distribution and water uptake in hydrocarbon and perfluorinated proton-exchange membranes as studied by NMR cryoporometry (original) (raw)
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Thermal studies of the state of water in proton conducting fuel cell membranes
Journal of Power Sources, 2007
The thermodynamics of acid group hydration was studied for different membranes (including Nafion ® and sulfonated poly(arylene ether sulfone) (BPSH)) and model systems (including an organic/inorganic composite (I/O) and a multiblock polymer (MB-150)). Experiments were carried out with the membranes exposed to different activities of water corresponding to different levels of membrane hydration. Isopiestic sorption shows a significantly greater uptake in water for the multiblock polymer as compared to the others. Differential scanning calorimetry (DSC) was used to study thermal properties to elucidate the state of water in the membranes. A comparison is made of various modes of collecting data using DSC. Based on these data, we discuss the overall understanding of water interactions with these membranes as well as the limitations of thermodynamic data in describing microenvironments within the membrane.
Polymer, 2009
The relationships between morphology and proton conduction for Nafion membranes and hydrocarbontype proton exchange membranes, namely, sulfonated poly(arylene ether ether ketone) (S-PEEK) and sulfonated poly(arylene ether sulfone) (S-PES), were investigated by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The direct simultaneous observation of surface morphology and active regions of proton conduction on membranes by combined high-resolution AFM phase imaging and an electrochemical technique at controlled humidity provided significant morphological information, particularly for the hydrocarbon-type membranes that exhibit few or no features on SAXS profiles. For the Nafion membranes, the active proton paths became denser and congregated with each other at over 60% RH, resulting in the formation of well-connected networks. For the hydrocarbon-type membranes, however, only the relatively small and dispersed proton paths were observed, which showed no significant change even as water content increased. We have demonstrated that the differences in microscopic morphology between the Nafion and hydrocarbon-type membranes are associated with the differences between their macroscopic proton conductivities.
Sulfonated poly (arylene ether sulfone) proton exchange membranes for fuel cell applications
Green Processing and Synthesis, 2015
Sulfonated poly (arylene ether sulfone) membranes were synthesized by direct copolymerization of 4,4-bis (4-hydroxyphenyl) valeric acid, 4,4′-difluorodiphenyl sulfone and synthesized sulfonated 6F-bisphenol-A/ bisphenol-A as novel proton exchange membranes for fuel cell applications. Prepared membranes were subsequently crosslinked with synthesized 6F-bisphenol-A based epoxy resin (EFN) by thermal curing reaction keeping in view the resilience and toughness of the membranes. The structural characterization was done by using Fourier transform infrared (FTIR), 1 H nuclear magnetic resonance (NMR) and 13 C NMR techniques. Proton conductivity of the membranes was determined by a four-point probe technique. Methanol permeability was determined by using a diffusion cell in which concentration of the liquids was determined by UV-spectroscopic technique. The enhancement in mechanical properties determined by a universal testing machine and also a better oxidative stability were observed for the crosslinked membranes. However, a decrease in their water and methanol absorption, ion exchange capacity, proton conductivity and methanol permeability was observed. This was due to the reduction in the numbers of ionic channels in case of crosslinked membranes which was confirmed by carrying out morphological analysis of the membranes using atomic force microscopy. In addition, X-ray diffraction measurement by XPERT-PRO diffractometer was also used for structural characterization. Crosslinked membranes showed better thermal stability as determined by thermogravimetric analysis and differential scanning calorimetry.
Journal of Power Sources, 2007
In the present study, we examine the water and proton transport properties of hexafluorinated sulfonated poly(arylenethioethersulfone) (6F-SPTES) copolymer membranes for applications to proton exchange membrane fuel cells (PEMFCs). The 6F-SPTES copolymer membranes build upon the structures of previously studied sulfonated poly(arylenethioethersulfone) (SPTES) copolymer membranes to include CF 3 functional groups in efforts to strengthen water retention and extend membrane performance at elevated temperatures (above 120 • C). The 6F-SPTES copolymer membranes sustain higher water self-diffusion and greater proton conductivities than the commercial Nafion ® membrane. Water diffusion studies of the 6F-SPTES copolymer membranes using the pulsed-field gradient spin-echo NMR technique reveal, however, the fluorinated membranes to be somewhat unfavorable over their non-fluorinated counterparts as high temperature membranes. In addition, proton conductivity measurements of the fluorinated membranes up to 85 • C show comparable results with the non-fluorinated SPTES membranes.
Interfacial Water-Transport Effects in Proton-Exchange Membranes
2009
It is well known that the proton-exchange membrane is perhaps the most critical component of a polymer-electrolyte fuel cell. Typical membranes, such as Nafion(R), require hydration to conduct efficiently and are instrumental in cell water management. Recently, evidence has been shown that these membranes might have different interfacial morphology and transport properties than in the bulk. In this paper, experimental
NMR Characterization of Composite Polymer Membranes for Low-Humidity PEM Fuel Cells
Journal of The Electrochemical Society, 2007
Composite membranes prepared by incorporating SiO 2 , TiO 2 , or Zr͑HPO 4 ͒ 2 particles into Nafion exhibit enhanced performance in proton exchange membrane ͑PEM͒ fuel cells tested at elevated temperatures compared to filler-free Nafion when operating under lower relative humidity. Water-transport properties of these membranes were investigated by nuclear magnetic resonance ͑NMR͒ methods, including pulsed-field-gradient spin-echo diffusion, spin-lattice relaxation, and spectral measurements. At least two distinct water environments are observed in all materials, and the enhanced water uptake of the composites, relative to filler-free Nafion, is attributed to alteration of the pore structure of the membrane.
Chemical Physics …, 2008
Enthalpy of activation for proton exchange processes in fully hydrated hybrid sulfonated poly(ether ether ketone)-silica (SPEEK/SiO 2 ) membranes were measured from the 1 H NMR spectra under magic angle sample spinning (MAS). For the first time Eyring function is used for this purpose. Two exchange processes between different water pools were detected. The isotropic chemical shift of the 1 H spectrum allows us to obtain information about the normalized enthalpy of activation characterizing the water exchange. These results show that the proton exchange membranes performances could be improved by addition of small concentrations of silica in the range of 5-10 wt.%.
2004
This paper reports the effect of sulfonation processon thermal behavior and microstrucutre of sulfonated polysulfone membrane. Various degree of sulfonation reactin has been conducted and the sulfonated membranes were characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), x-ray diffraction (XRD) and scanning electron microscopy (SEM). Modifications of the origin polysulfone polymer resulted in an increment value of glass transition temperature (Tg) due to the introduction of sulfonic acid group to the polymer backbone. However, due to some hindrance such as trace amount of organic solvent left during solvent evaporation and high hydrophilicity of the produced sulfonated membranes resulted in decreasing values of Tg. The polymer membrane showed lower degradation temperature as a function of degree of sulfonation. From XRD analysis, it was found that the membrane shows slight crystalline behavior after the sulfonation reaction. Detail discussions and observation of the alteration in microstructure of the sulfonated membrane were supported by SEM micrograph.