Conductivity Of Proton Exchange Membranes Research Articles

A Novel Composite Nafion/Anodized Aluminium Oxide Proton Exchange Membrane

AbstractThe high proton conductivity of proton exchange membranes (PEMs) made of Nafion® is attributed to a random 3D network of elongated water channels formed by bundles of rod‐like inverted micelles. Alignment of bundles, e.g., by stretching, is known to significantly enhance the in‐plane conductivity, yet achieving alignment normal to the membrane surface, desired for most applications, is challenging. A few attempts to obtain such alignment by confining Nafion in nanometric trans‐membrane pores of solid anodized aluminium oxide (AAO) membranes were reported, so far with limited success. Here we demonstrate that considerable pore filling of AAO with 200 nm pores by Nafion could be achieved through (i) use of Nafion concentrations below the threshold concentration C*, above which Nafion molecules form large aggregates; and (ii) control of filling rate through a combination of thermal and vacuum evaporation of Nafion solution through the membrane. The proton conductivity and NaCl diffusion permeability (sodium chloride diffusivity) tested by electrochemical impedance spectroscopy demonstrated superior intrinsic conductivity and selectivity of the composite membrane as compared to commercial Nafion membranes.

Enhanced proton conductivity of proton exchange membranes by incorporating phosphorylated hollow titania spheres

The synergistic enhancement in proton conductivity of hybrid membranes by improving the water retention capacity and introducing additional proton transfer sites is reported.

Enhanced water retention and low-humidity proton conductivity of sulfonated poly(ether ether ketone) hybrid membrane by incorporating ellipsoidal microcapsules

Two kinds of polymeric ellipsoidal microcapsules (EMCs) with different functional groups (phosphoric acid groups and imidazole groups) were synthesized via precipitation polymerization and incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare hybrid membranes. The structure, thermal stability and composition of EMCs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The quasi-one dimensional structure endowed EMCs with high water uptake and water retention. Especially, for the hybrid membranes filled with 5 wt.% phosphoric acid-functionalized polymeric EMCs, water uptake was increased from 19.0% for pristine SPEEK membranes to 58.2%, and the water retention was 15.1% after 180 min testing at 40 °C and 20% RH, which is threefold and ninefold higher than those of pristine SPEEK membranes, respectively. Particularly, the proton conductivity at low RH was still up to 3.51 × 10−3 S/cm after 60 min testing. The results manifested that the ellipsoidal microcapsules, as a new kind of filler, had great potential in enhancing the water retention and low-humidity proton conductivity of proton exchange membranes.

Measuring water hydrogen bonding distributions in proton exchange membranes using linear Fourier Transform Infrared spectroscopy

This paper describes a linear Fourier Transform Infrared (FTIR) spectroscopic method for measuring the hydrogen bonding distribution of water sorbed in proton exchange membranes. This information on the distribution of the microenvironments of water in an ionic polymer is critical to understanding the effects of different acidic groups on the proton conductivity of proton exchange membranes at low relative humidity. The OD stretch of dilute HOD in H2O has a single, well-defined vibrational band. When HOD in dilute H2O is sorbed into a proton exchange membrane, the OD stretch peak appears to shift based on the microenvironment that water encounters within the nanophase separated structure of the material. This peak shift is a signature of different hydrogen bonding populations within the membrane, which can be deconvoluted rigorously for dilute HOD in H2O compared to only qualitative observations that can be made with pure D2O or H2O. The theory and experimental practice of determining the hydrogen bonding distribution of water in a range of proton exchange membranes bearing aromatic sulfonate and perfluorosulfonate groups using this OD stretch technique are discussed.

Enhanced water retention and proton conductivity of proton exchange membranes by incorporating hollow polymer microspheres grafted with sulfonated polystyrene brushes

The paper describes the synthesis of hollow polymer microspheres with sulfonated polystyrene brushes and investigation of the enhanced water retention and proton conductivity of proton exchange membranes.

Metal–organic framework–graphene oxide composites: a facile method to highly improve the proton conductivity of PEMs operated under low humidity

Nafion based proton exchange membranes (PEMs) modified by a metal–organic framework–graphene oxide composite (ZIF-8@GO) are reported.

Investigations of crystallinity and chain entanglement on sorption and conductivity of proton exchange membranes

Proton-conducting hydrocarbon membranes often require an ion exchange capacity (IEC) in excess of 2mmeq/g to achieve a conductivity sufficiently high for technological applications (typically >50mS/cm). Membranes with high IEC are often brittle when dry and swell excessively when fully hydrated. Increasing the crystallinity of hydrocarbon membranes is hypothesized to increase phase segregation thereby enhancing their mechanical integrity in water by reducing their propensity to swell excessively, and to provide an ionic network when water contents are reduced when RH<100% and under elevated temperatures. In this work we examine the effect of increasing the crystallinity of highly sulfonated graft copolymer membranes by blending with polycrystalline poly(vinylidene difluoride) (PVDF). The addtion of PVDF increases the crystallinity, reduces the ion exchange capacity, reduces swelling, yet does not deleteriously affect proton conductivity. The extent to which crystalinity increases and water swelling is reduced was found dependent on the molecular weight of the PVDF. The incorporation of high m. wt. PVDF enhanced crystallinity to a lesser degree than incorporating low m. wt. PVDF but swelling was reduced to a greater extent. This observation is explained by an increase in elastic forces of the membrane that oppose osmotic swelling due to an increase in physical connectivity of the PVDF crystallites via long PVDF polymer chains that span multiple crystallites. The addition of PVDF did not compromise proton mobility in the ionic phase and as a consequence of the much higher proton concentrations attained, proton conductivities were significantly enhanced. Finally, the properties of membranes containing different ratios of ionomer and high m. wt. PVDF are described. Optimal compositions of these components are found in membranes which possess minimal swelling in water and have proton conductivity that is less susceptible to large fluctuations in RH.

Enhanced proton conductivity of proton exchange membranes by incorporating sulfonated metal-organic frameworks

In this study, octahedral crystal MIL101(Cr) with a uniform size of ∼400 nm is synthesized via hydrothermal reaction. It is then functionalized with sulfonic acid groups by concentrated sulfuric acid and trifluoromethanesulfonic anhydride in nitromethane. The sulfonated MIL101(Cr) are homogeneously incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare hybrid membranes. The performances of hybrid membranes are evaluated by proton conductivity, methanol permeability, water uptake and swelling property, and thermal stability. The methanol permeability increased slightly from 6.12 × 10−7 to 7.39 × 10−7 cm2 s−1 with the filler contents increasing from 0 to 10 wt. %. However, the proton conductivity of the hybrid membranes increased significantly. The proton conductivity is increased up to 0.306 S cm−1 at 75 °C and 100% RH, which is 96.2% higher than that of pristine membranes (0.156 S cm−1). The increment of proton conductivity is attributed to the following multiple functionalities of the sulfonated MIL101(Cr) in hybrid membranes: i) providing sulfonic acid groups as facile proton hopping sites; ii) forming additional proton-transport pathways at the interfaces of polymer and MOFs; iii) constructing hydrogen-bonded networks for proton conduction via –OH provided by the hydrolysis of coordinatively unsaturated metal sites.

4,4′-Oxydianiline (ODA) containing sulfonated polyimide/protic ionic liquid composite membranes for anhydrous proton conduction

The aim of this study was to utilize ionic liquids (ILs) in preparation of modified sulfonated polyimide (SPI) composite membranes to substantially increase the conductivity of proton exchange membranes (PEMs). Protic ILs used included 1-vinylimidazolium trifluoromethanesulfonate [ImVH][OTf] and 1-methyl-imidazolium trifluoromethanesulfonate [ImMH][OTf]. SPIs are synthesized from diamine, 2,2-bis[4-(4-amino-phenoxy)phenyl]propane (BAPP), sulfonated diamine, 4,4′-diamino diphenyl ether-2,2′-disulfonic acid (ODADS), and an aromatic anhydride, ODPA (4,4′-oxy diphthalic anhydride). ODADS improves conductivity, while BAPP enhances the mechanical and thermal properties of SPIs. We have prepared SPI/IL composite PEM using 50 wt.% [ImVH][OTf] with a high conductivity of 3–6 mS/cm at 120 °C and anhydrous condition depending on the ODADS content. [ImVH][OTf] offered better conductivity, which can be attributed to its chemical structure that has a vinyl group attached to an imidazolium ring to provide lower melting temperature and lattice energy, thereby increasing conductivity.

Electro-casting of proton exchange membranes from a heterogeneous solution

A novel solution casting method of membrane preparation is explored to improve the conductivity of proton exchange membranes (PEMs). A high voltage alternative electric field is applied to a heterogeneous Nafion solution while evaporating the solvents, leaving aligned proton channels in the solidified membrane, and SAXS and WAXS have been given as direct evidences. Therefore, the trans-plane conductivity of the PEM is increased. A Non-solvent of low polarity carbon tetrachloride (CCl4) causes phase separation in the casting solution, which facilitates the Nafion ionomer to respond to the applied electric field. Despite the severe phase separation in the casting solution, the resultant electro-casting membrane shows a higher mechanical strength than that of the normal recast Nafion membrane.

Electric field processing to control the structure of titanium oxide/sulfonated poly (ether ether ketone) hybrid proton exchange membranes

With the aim to improve the conductivity of proton exchange membranes (PEMs), an external AC electric field is applied to a sulfonated poly (ether ether ketone) (SPEEK)-titanium (IV) oxide (TiO2) hybrid casting solution during solvent evaporation. Present technique gives a potentially useful method to fabricate PEMs with oriented proton channels, and resulting in increased conductivity by 75% in the trans-plane direction versus normal methods. In addition, reciprocation of TiO2 under the AC electric field prevents the nanoparticles from aggregating and improves mechanical strength of the PEMs. Factors affect the proton channels' alignment degree such as the applied field magnitude and frequency are also investigated.

Highly proton conductive electrolyte membranes: Fiber-induced long-range ionic channels

Novel conductive inorganic fiber/polymer hybrid proton exchange membranes (PEMs) were obtained by taking advantage of sulfated zirconia (S-ZrO 2) fibers made by electrospinning and post-electrospinning processes. Induced by electrospun inorganic fibers, long-range ionic channels were formed by agglomerating functional groups, which served as continuous hopping pathways for protons and significantly improved the proton conductivity of PEMs.

Influence of Morphology of Block Copolymers on the Conductivity of Proton Exchange Membranes

not Available.

Proton conductivity measurements of PEM performed in EasyTest Cell

The paper presents dc measurements of proton exchange membranes (PEMs) as an integral part of a membrane electrode assembly (MEA) performed in a novel EasyTest Cell testing device. Depending on their operating temperature PEMs are divided in two groups. The commercial Nafion membranes (Alfa Aesar) as well as the self-prepared interpenetrating network of poly(acrylamidepropylsulfonic acid) and poly(acrylamide) (PAMPS–PAM), and Nafion 117 with grafted PAMPS chains (Nafion graft-PAMPS) are tested in the low temperature range (upto 80 °C). The PEMs from the second group (prepared in the frame of EU project AUTOBRANE, FP 6) – phosphoric acid doped polybenzimidazole (PBI/PA) and PBI, containing cross-linked poly(vinylphosphonic acid) (CR-PVPhA) – are investigated for high temperature applications (120–200 °C). The EasyTest Cell is a three electrode electrochemical test that offers the possibility to obtain steady state polarization curves at strict self-regulated constant hydrogen and water vapor partial pressures. The initial slope of the polarization curves, corrected by the electronic resistance of the electrodes under study is used as a criterion for the proton conductivity of the investigated PEMs. The results obtained for the commercially available Nafion are in a good agreement with the available literature data. The PAMPS grafting from Nafion 117 results in 1.5 fold higher proton conductivity compared to the non-grafted one. The proton conductivity of the PBI/PA membrane is almost independent on the relative humidity (RH) in the range of 15–40% (0.110–0.117 S cm −1 at 180 °C) which makes the water management redundant, this way facilitating the fuel cell management. The proton conductivity of the PBI/CR–PVPhA membrane is in the range of 7 × 10 −3 S cm −1 (170 °C, 20% RH). The EasyTest Cell working principle and single chamber design allows precise control of vital working parameters (temperature and RH) for the proton conductivity of PEM.

Ionic conductivity of proton exchange membranes

Proton conductivity of a series of proton exchange membranes based on sulfonated αββ-trifluorostyrene- co-substituted-αββ-trifluorostyrenes (BAM ®) (equivalent weight, EW, 735–407 g mol −1) and sulfonated styrene–(ethylene–butylene)–styrene triblock copolymers (DAIS-Analytical) (EW 585–1062 g mol −1) was determined by ac impedance spectroscopy. These data are compared to previously published data on Nafion ® 117 and ethylenetetrafluoroethylene- g-polystyrene sulfonic acid membranes. A correlation exists between the membrane's conductivity, its water content, the ratio of water to ionic sites, and the overall proton concentration. These factors are determined by the membrane's equivalent weight and chemical structure. SAXS spectra for the sulfonated styrene–(ethylene–butylene)–styrene triblock copolymer membranes were featureless. BAM ® membranes, however, show distinct scattering indicative of ionic aggregates. An interparticle model fit the scattering intensities. The volume fraction of ionic aggregates in the film was a maximum with membranes of intermediate equivalent weight but in all cases much lower than the water content of the membrane, i.e. phase separation of hydrophilic and hydrophobic domains is not extensive. TEM analysis of dry membranes also indicates that phase separation, although evident, is not extensive. These results lead to the conclusion that large majority of sulfonic acid sites are dispersed homogeneously through the membrane.