Qing Lin Liu

Enhancement of hydroxide conductivity by grafting flexible pendant imidazolium groups into poly(arylene ether sulfone) as anion exchange membranes

Anion exchange membranes (AEMs) have been recognized as one of the most prospective polyelectrolytes for fuel cells due to their faster electrode reaction kinetics and the potential of adopting cheaper metal catalysts against proton exchange membranes (PEMs). Herein, a series of poly(arylene ether sulfone)s containing a flexible pendant imidazolium cation were synthesized by grafting bromine-bearing imidazolium-based ionic liquids into a hydroxyl-bearing poly(ether sulfone) matrix. 1H NMR spectroscopy was used to confirm the as-synthesized copolymers. Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) were used to characterize the morphology of the membranes. The incorporation of the flexible side-chain imidazolium groups is beneficial to the aggregation of the ionic clusters leading to the formation of hydrophilic/hydrophobic phase-separated morphology and nano-channels. As a result, an enhancement in the ionic conductivity can be achieved. Therefore, the as-prepared AEMs possess higher ionic conductivity than traditional benzyl-type AEMs. The weight-based ion exchange capacity (IECw) of the membranes was in the range of 1.01–1.90 meq. g−1. Correspondingly, their ionic conductivity was in the range of 22.13–59.19 and 51.66–108.53 mS cm−1 at 30 and 80 °C, respectively. Moreover, the membranes also exhibit good alkaline stability and interesting single cell performance. This work presents a facile and universal route for the synthesis of AEMs with superior performance.

Phenolphthalein-based Poly(arylene ether sulfone nitrile)s Multiblock Copolymers As Anion Exchange Membranes for Alkaline Fuel Cells

A series of phenolphthalein-based poly(arylene ether sulfone nitrile)s (PESN) multiblock copolymers containing 1-methylimidazole groups (ImPESN) were synthesized to prepare anion exchange membranes (AEMs) for alkaline fuel cells. The ion groups were introduced selectively and densely on the unit of phenolphthalein as the hydrophilic segments, allowing for the formation of ion clusters. Strong polar nitrile groups were introduced into the hydrophobic segments with the intention of improving the dimensional stability of the AEMs. A well-controlled multiblock structure was responsible for the well-defined hydrophobic/hydrophilic phase separation and interconnected ion-transport channels, as confirmed by atomic force microscopy and small angle X-ray scattering. The ImPESN membranes with low swelling showed a relatively high water uptake, high hydroxide ion conductivity together with good mechanical, thermal and alkaline stability. The ionic conductivity of the membranes was in the range of 3.85-14.67×10(-2) S·cm(-1) from 30 to 80 °C. Moreover, a single H2/O2 fuel cell with the ImPESN membrane showed an open circuit voltage of 0.92 V and a maximum power density of 66.4 mW cm(-2) at 60 °C.

Molecular Simulation of Water/Alcohol Mixtures' Adsorption and Diffusion in Zeolite 4A Membranes

The COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) force field with two sets of partial atomic charges of water was used to simulate adsorption and diffusion behavior of water/methanol and water/ethanol mixtures in zeolite 4A at 298 K. The adsorption of alcohol first increased and then decreased with increasing pressure, whereas the adsorption of water increased progressively until an adsorption equilibrium was reached. Both the adsorbed molecules and the zeolite framework were treated as a fully flexible model in MD simulations. The simulation results show that the effects of the size and steric hindrance of the diffusing molecules on diffusivity are significant. The diffusivity of water, methanol, and ethanol molecules decreases by 1 order of magnitude in the order of water > methanol > ethanol. The diffusivity of water molecules depends on the mass fraction and the partial charges of water in zeolite 4A. The ethanol and methanol molecules have restricted motion through the alpha-cages, whereas the water molecules can easily pass through the alpha-cages window at low feed alcohol concentrations. And the extent of hydrogen bonding increased with increasing water concentration.

Modeling of esterification of acetic acid with n-butanol in the presence of Zr(SO4)2·4H2O coupled pervaporation

Abstract Modeling of esterification of acetic acid with n -butanol in the presence of Zr(SO 4 ) 2 ·4H 2 O coupled pervaporation was studied in this paper. The influence of several process variables, such as process temperature, initial mole ratio of acetic acid over n -butanol, the ratio of the effective membrane area over the volume of reacting mixture and catalyst content, on the esterification was discussed. The calculated results for the conversion of n -butanol to water and permeation flux were consistence with the experimental data. The permselectivity and water content can be roughly estimated by the model equations.

Imidazolium-Functionalized Poly(arylene ether sulfone) Anion-Exchange Membranes Densely Grafted with Flexible Side Chains for Fuel Cells

With the intention of optimizing the performance of anion-exchange membranes (AEMs), a set of imidazolium-functionalized poly(arylene ether sulfone)s with densely distributed long flexible aliphatic side chains were synthesized. The membranes made from the as-synthesized polymers are robust, transparent, and endowed with microphase segregation capability. The ionic exchange capacity (IEC), hydroxide conductivity, water uptake, thermal stability, and alkaline resistance of the AEMs were evaluated in detail for fuel cell applications. Morphological observation with the use of atomic force microscopy and small-angle X-ray scattering reveals that the combination of high-local-density-type and side-chain-type architectures induces distinguished nanophase separation in the AEMs. The as-prepared membranes have advantages in effective water management and ionic conductivity over traditional main-chain polymers. Typically, the conductivity and IEC were in the ranges of 57.3-112.5 mS cm(-1) and 1.35-1.84 mequiv g(-1) at 80 °C, respectively. Furthermore, the membranes exhibit good thermal and alkaline stability and achieve a peak power density of 114.5 mW cm(-2) at a current density of 250.1 mA cm(-2). Therefore, the present polymers containing clustered flexible pendent aliphatic imidazolium promise to be attractive AEM materials for fuel cells.

Side-chain-type anion exchange membranes bearing pendant quaternary ammonium groups via flexible spacers for fuel cells

To realize high performance anion exchange membranes (AEMs) for alkaline fuel cells (AFCs), a series of quaternized poly(ether sulfone)s (PESs) with different lengths of flexible spacers linking cationic groups and the backbone was synthesized via nucleophilic polycondensation, demethylation and Williamson reactions. Atomic force microscopy (AFM) phase images show clear hydrophilic/hydrophobic phase separation for all the side-chain-type AEMs. The PES-n-QA membrane with hexyleneoxy spacers (n = 6) between the cationic groups and backbone (benzene ring) exhibited the maximum conductivity of 62.7 mS cm−1 (IEC = 1.48 meq. g−1) at 80 °C. The AEM materials are found to have an improved long-term alkaline stability by extending the length of the flexible spacer (n ≥ 4). The PES-12-QA membrane with a flexible dodeceneoxy spacer demonstrated the highest alkaline stability, where the conductivity and IEC only decreased by 8.1% and 6.9% after immersing in a 1 M aqueous KOH solution at 60 °C for 720 h. Furthermore, the single fuel cell performance test using PES-6-QA as an AEM showed a maximum power density of 108.3 mW cm−2 at a current density of 250 mA cm−2 at 60 °C.

Characterization and Permeation Performance of Novel Organic-Inorganic Hybrid Membranes of Poly(vinyl Alcohol)/1,2-Bis(triethoxysilyl)ethane

Bis(trialkylsilyl) precursor was used to modify polymer membranes for the first time. Novel organic-inorganic hybrid membranes of poly(vinyl alcohol) (PVA)/1,2-bis(triethoxysilyl)ethane (BTEE) were prepared through a sol-gel method for pervaporation dehydration of ethanol. The permeability and selectivity of the membranes were improved simultaneously. The physicochemical properties of the hybrid membranes were investigated. With increasing BTEE content, the amorphous region in the hybrid membranes increased and became more compact. Phase separation took place in the hybrid membranes containing abundant BTEE, and silica particles distributed in the PVA matrix homogeneously. Compared to PVA membranes, the hybrid membranes exhibit high thermal stability and improved separation performances. Silica-hybrids reduced significantly the swelling of PVA membranes in an aqueous solution. The Flory-Huggins interaction parameter of water with membranes chi13 increased with increasing BTEE content, whereas that of ethanol with membranes chi23 decreased. Diffusion behavior of water and ethanol through the membranes were analyzed using the Maxwell-Stefan equation. When BTEE content was below 6 wt%, diffusion coefficient of water D13 increased remarkably and that of ethanol D23 decreased slightly.

Structure and permeation of organic–inorganic hybrid membranes composed of poly(vinyl alcohol) and polysilisesquioxane

Organic–inorganic hybrid membranes with high separation performance were prepared by the incorporation of polysilisesquioxane (PSS) into a poly(vinyl alcohol) (PVA) matrix in order to solve the trade-off relationship between the selectivity and permeability of PVA membranes. The incorporation of the PSS resulted in a change in the physical and chemical structure of the hybrid membranes. The crystalline region in the hybrid membranes decreased with increasing PSS content. The hydrophilicity of the hybrid membranes increased when the PSS content is below 3 wt%, and then decreased. Silica particles formed on the surface and in the interior of the hybrid membranes due to the PSS conglomeration, and the surface roughness of the hybrid membranes increased linearly with increasing PSS content. The trade-off between permeability and selectivity was successfully solved using the hybrid membranes in pervaporation dehydration of tetrahydrofuran. The permselectivity and flux of the hybrid membranes increased simultaneously when the PSS content was below 2 wt%, whereas the permselectivity decreased when the PSS content was above 2 wt%. The hybrid membrane containing 2 wt% PSS had the highest separation factor of 1810.

A Fully Flexible Potential Model for Carbon Dioxide

National Natural Science Foundation of China [50573063]; Program for New Century Excellent Talents in University of the State Ministry of Education [NCET-05-0566]; Specialized Research Fund for the Doctoral Program of Higher Education of China [2005038401]

UV-crosslinked chitosan/polyvinylpyrrolidone blended membranes for pervaporation

Chitosan is an important biomacromolecule and polyvinylpyrrolidone (PVP) is a biocompatible synthetic polymer. The crosslinked chitosan/PVP blended membranes were prepared via UV irradiation. The as-prepared membranes have a highly crosslinked chitosan/PVP network structure originated from self-crosslinking of PVP and branching of chitosan onto PVP chains during UV irradiation. UV-Crosslinking significantly enhanced the mechanical strength and thermal stability of the blended membranes. Their highest tensile strength is twice as much as that of the pristine chitosan membrane. Maintaining the same swelling degree of the pristine chitosan membrane, the blended membranes have high sorption selectivity towards methanol and water. The as-prepared membranes exhibit an excellent performance in pervaporation separation of methanol/ethylene glycol and water/ethanol and show great potential as new biomedical materials and in the removal of alcohol and water from organics.