SPES Membrane Research Articles

PWA/silica doped sulfonated poly(ether sulfone) composite membranes for direct methanol fuel cells

A novel sulfonated poly(ether sulfone) (SPES)/phosphotungstic acid (PWA)/silica composite membranes for direct methanol fuel cells (DMFCs) application were prepared. The structure and performance of the obtained membranes were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), water uptake, proton conductivity, and methanol permeability. Compared to a pure SPES membrane, PWA and SiO2 doped membranes had a higher thermal stability and glass transition temperature (Tg) as revealed by TGA-FTIR and DSC. The morphology of the composite membranes indicated that SiO2 and PWA were uniformly distributed throughout the SPES matrix. Proper PWA and silica loadings in the composite membranes showed high proton conductivity and sufficient methanol permeability. The selectivity (the ratio of proton conductivity to methanol permeability) of the SPES-P-S 15% composite membrane was almost five times than that of Nafion 112 membrane. This excellent selectivity of SPES/PWA/silica composite membranes indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The effects of aspect ratio of inorganic fillers on the structure and property of composite ion-exchange membranes

A new type of nanocomposite ion-exchange membranes containing sulfonated polyethersulfone (sPES) polymer matrix and sulfonated surface-functionalized mesoporous silica (SS) inorganic fillers was prepared. Various characterizations revealed that the addition of inorganic fillers with different shapes had a significant influence on the membrane structure. The mesoporous inorganic fillers not only created extra pore and water channels, assisting the ionic migration and improving conductivity of the composites, but also provided additional fixed charge groups upon surface modification. This allows the Donnan exclusion to work effectively and thus improve the selectivity of membranes. It was proved that the incorporation of appropriate amount of SS additive could significantly improve the conductivity (up to 20 folds) and permselectivity (about 14%) of the sPES membranes. The performance of these newly developed membranes in desalination by electrodialysis was comparable with that of a commercial membrane (FKE).

Sulfonated poly(ether sulfone)/phosphotungstic acid/attapulgite composite membranes for direct methanol fuel cells

AbstractNovel composite sulfonated poly(ether sulfone)(SPES)/phosphotungstic acid (PWA)/attapulgite (AT) membranes were investigated for direct methanol fuel cells (DMFCs). Physical–chemical properties of the composite membranes were characterized by FTIR, DSC, TGA, SEM‐EDX, water uptake, tensile test, proton conductivity, and methanol permeability. Compared with a pure SPES membrane, PWA, and AT doping in the membrane led to a higher thermal stability and glass transition temperature (Tg) as revealed by TGA and DSC. Tensile test indicated that lower AT content (3%) in the composite can significantly increase the tensile strength, while higher AT loading demonstrated a smaller contribution on strength. Proper PWA and AT loadings in the composite membranes can increase the proton conductivity and lower the methanol cross‐over. The proton conductivity of the SPES‐P‐A 10% composite membrane reached 60% of the Nafion 112 membrane conductivity at room temperature while the methanol permeability was only one‐fourth of that of Nafion 112 membrane. This excellent performances of SPES/PWA/AT composite membranes could indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Sulfonated poly(arylene ether sulfone) membrane containing sulfated zirconia for high-temperature operation of PEMFCs

A new composite membrane that consists of sulfonated poly(arylene ether sulfone) (SPES) and a highly functionalized inorganic filler of sulfated zirconia (s-ZrO2) was synthesized and evaluated for enhancement of water retention as well as proton conductivity at high temperatures above 120 °C in the absence of water. Since the SPES has less hydrophobic/hydrophilic difference between the polymer backbone and –SO3H ionic groups, the proton channels are relatively small and not easily distributed, which results in no significant change at highly saturated conditions. Therefore, the effective interconnection between the –SO3H ionic groups and bound water adsorbed on the surface of the s-ZrO2 is the key in achieving a higher proton transfer for PEM fuel cells at high temperatures above 120 °C. Analysis by small angle X-ray scattering (SAXS) of recast membranes showed that SPES random copolymers with various s-ZrO2 contents have a similar ionic cluster size and less pronounced phase separation regardless of the dry/swollen condition of the membrane. However, the phase images obtained by atomic force microscopy (AFM) showed that the connectivity of ionic groups varies, depending on the content of s-ZrO2 in the polymer matrix. Larger and more interconnected hydrophilic regions were found with the SPES membrane when there was no significant particle aggregation in the hydrophilic moieties of the polymer matrix. In this study, the composite membrane with 5 wt% s-ZrO2 had the highest proton conductivity at 120 °C due to better ionic interactions as well as the presence of bound water combined with the –SO3H ionic groups.

Sulfonated Poly(arylene ether sulfone)s with Phosphine Oxide Moieties: A Promising Material for Proton Exchange Membranes

Sulfonated poly(arylene ether sulfone)s with phosphine oxide moieties (sPESPO) were achieved by polycondensation of bis(4-hydroxyphenyl)phenylphosphine oxide with 3,3'-disulfonate-4,4'-difluorodiphenyl sulfone (SFDPS) and 4-fluorophenyl sulfone (FPSF). Sulfonated poly(arylene ether sulfone)s (sPES) were also synthesized by polymerization of 4,4'-sulfonyldiphenol with SFDPS and FPSF for comparison. The comparative study demonstrates that the sPESPO ionomers exhibit strong intermolecular interactions and high oxidative stability because of the phosphine oxide groups. Furthermore, the sPESPO membrane and the sPES membrane with an equal ion exchange capacity show much different nanophase separation morphology. As a result, the former shows better properties than the latter. The sPESPO membranes exhibit excellent overall properties. For instance, the sPESPO membrane, with a disulfonation degree of 45%, exhibits high thermal and oxidative stability. Moreover, it shows a water uptake of 30.8% and a swelling ratio of 15.8% as well as a proton conductivity of 0.087 S/cm at 80 degrees C.

Electron spin resonance investigation of the effects of methanol on microscopic viscosity, ordering, and polarity in different phases of ionomer membranes with sulfonated polyarylene backbones

Membranes constituted from sulfonated poly (arylene ether sulfone) (SPES) and sulfonated poly(ether ether ketone) (SPEEK) are characterized using electron spin resonance (ESR) to monitor the local environment of the TEMPONE spin probe (2,2,6,6-tetramethyl-4-piperidone N-oxide). The probe occupies two phases of very different polarities and mobilities in both the swollen SPES and SPEEK membranes. ESR lineshape analysis allows the individual phases to be characterized in terms of their microviscosity, local polarity, and solvent ordering. The effects of sulfonation and methanol on the individual phase properties were studied by equilibrating different membranes with water–methanol mixtures over the full range of compositions. At sulfonation levels below 50%, SPES and SPEEK membranes have numerous but smaller, elongated hydrophilic domains in which lead to restricted motion and partial ordering of the probes in comparison with Nafion. The less polar phase of the aromatic polymers is attributed to a probe population associated with the polymer backbone. Methanol penetrates this region and disrupts the backbone structure at a concentration that depends upon the level of sulfonation.

Sulfonated poly(ether sulfone)/silica composite membranes for direct methanol fuel cells

AbstractA series of sulfonated poly(ether sulfone) (SPES)/silica composite membranes were prepared by sol–gel method using tetraethylorthosilicate (TEOS) hydrolysis. Physico–chemical properties of the composite membranes were characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), scanning electron microscope–energy dispersive X‐ray (SEM–EDX), and water uptake. Compared to a pure SPES membrane, SiO2 doping in the membranes led to a higher thermal stability and water uptake. SEM–EDX indicated that SiO2 particles were uniformly embedded throughout the SPES matrix. Proper silica loadings (below 5 wt %) in the composite membranes helped to inhibit methanol permeation. The permeability coefficient of the composite membrane with 5 wt % SiO2 was 1.06 × 10−7 cm2/s, which was lower than that of the SPES and just one tenth of that of Nafion® 112. Although proton conductivity of the composite membranes decreased with increasing silica content, the selectivity (the ratio of proton conductivity and methanol permeability) of the composite membrane with 5 wt % silica loading was higher than that of the SPES and Nafion® 112 membrane. This excellent selectivity of SPES/SiO2 composite membranes could indicate a potential feasibility as a promising electrolyte for direct methanol fuel cell. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Highly charged and stable cross-linked 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS)-sulfonated poly(ether sulfone) polymer electrolyte membranes impervious to methanol

Disulfonated 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS) was synthesized as cross-linking agent. In situ cross-linking of sulfonated poly(ether sulfone) (SPES) via sulfonamide linkage was achieved using BAPBDS, for preparing polymer electrolyte membranes (PEMs), without deterioration in membrane functionality due to cross-linking. Effective cross-linking enhanced the membranes’ dimensional, thermal, and chemical stability without impairing the electro-chemical properties such as ion-exchange capacity and proton conductivity. Thus, the properties of the developed PEMs were significantly improved due to more compact structure of the cross-linked SPES membrane (CPES) over membranes without crosslinking. Comparable selectivity parameter (SP) and direct methanol fuel cell (DMFC) performance of the developed membranes, especially CPES-100, with Nafion 117 (N117) indicated their suitability for fuel cell applications.

Sulfonated poly(ether sulfone) (SPES)/boron phosphate (BPO 4) composite membranes for high-temperature proton-exchange membrane fuel cells

A new series of sulfonated poly(ether sulfone) (SPES)/boron phosphate (BPO 4) composite membranes for proton-exchange membrane fuel cells (PEMFCs) applications, with a BPO 4 content up to 40 wt%, were prepared by a sol–gel method using tripropylborate and phosphoric acid as precursors. Compared to a pure SPES membrane, BPO 4 doping in the membranes led to a higher thermal stability and glass-transition temperature ( T g) as revealed by TGA–FTIR, DSC and DMTA. Water uptake and oxidative stability were significantly increased by increasing the content of BPO 4. At both operating temperature conditions, namely 20 °C and 100 °C, the tensile strength of all the composite membranes were lower than that of the SPES membrane. However, even when the content of BPO 4 was as high as 30%, the composite membrane still possessed strength similar to the Nafion 112 membrane. SEM–EDX indicated that the BPO 4 particles were uniformly embedded throughout the SPES matrix, which may facilitate proton transport. Proton conductivities increased from 0.0065 to 0.022 S cm −1 at room temperature as BPO 4 increased from 0 to 40%. The conductivities also increased with the temperature. The SPES/BPO 4 composite membrane is a promising candidate for PEMFCs applications, especially at higher temperatures.

Development and characterization of sulfonated poly(ether sulfone) for proton exchange membrane materials

A series of sulfonated poly(ether sulfone) (SPES) were prepared by sulfonating poly(ether sulfone) with chlorosulfonic as sulfonating agent and concentrated sulfuric acid as solvent. Tough and ductile SPES membranes were obtained from DMAc solution. The degree of sulfonation (DS) and ion exchange capacity (IEC) were calculated via 1H NMR and titration. Microphase separated structure comprised of hydrophilic ionic clusters and hydrophobic polymer backbone were observed from atomic force microscopy (AFM) phase images. The hydrophilic ionic clusters became continuous to form channels when DS reached 0.50, corresponding to suddenly increase of water uptake. Combining AFM with water uptake analysis, we found SPES system reached a percolation threshold around DS of 0.39. SPES membranes with DS below 0.39 showed good dimensional stability in water, mechanical stability and oxidative stability. Proton conductivities ranged from 10 − 4 to 10 − 1 S/cm were measured at room temperature in water. SPES membranes exhibited lower methanol permeability than Nafion 112. A highest value of the proton conductivity-to-methanol permeability ratio was obtained for SPES with DS of 0.39. The results showed that SPES was promising for possible use in proton exchange membrane fuel cells, especially in direct methanol fuel cells.

Oxygen reduction and transport characteristics at a platinum and alternative proton conducting membrane interface

Kinetic and mass-transport properties were investigated for the oxygen reduction reaction for Nafion® 117 and sulfonated poly(arylene ether sulfone) membranes, both pre- and post-sulfonated analogs (SPES-40 & SPES-PS) under 100% relative humidity and as a function of pressure (1–4 atm total pressure, 323 K) and temperature (303–353 K, 3 atm) using a solid-state electrochemical cell. Kinetic parameters were obtained using slow-sweep voltammetry while mass-transport parameters, the diffusion coefficient ( D ) and solubility ( C ), were obtained using chronoamperometry at a Pt (microelectrode)|proton exchange membrane (PEM) interface. The oxygen reduction kinetics were found to be similar for all the membranes at the Pt microelectrode interface. The temperature dependence of O 2 permeation parameters showed identical trends for the membranes studied while the pressure dependence of O 2 permeation parameters displayed some differences. Despite higher ion exchange capacities and hence higher water uptake, the two SPES membranes exhibited relatively lower values of D as compared to Nafion® 117. The results are discussed in the context of their different microstructures.

Oxygen reduction and transport characteristics at a platinum and alternative proton conducting membrane interface

Kinetic and mass-transport properties were investigated for the oxygen reduction reaction for Nafion® 117 and sulfonated poly(arylene ether sulfone) membranes, both pre- and post-sulfonated analogs (SPES-40 & SPES-PS) under 100% relative humidity and as a function of pressure (1–4 atm total pressure, 323 K) and temperature (303–353 K, 3 atm) using a solid-state electrochemical cell. Kinetic parameters were obtained using slow-sweep voltammetry while mass-transport parameters, the diffusion coefficient ( D) and solubility ( C), were obtained using chronoamperometry at a Pt (microelectrode)|proton exchange membrane (PEM) interface. The oxygen reduction kinetics were found to be similar for all the membranes at the Pt microelectrode interface. The temperature dependence of O 2 permeation parameters showed identical trends for the membranes studied while the pressure dependence of O 2 permeation parameters displayed some differences. Despite higher ion exchange capacities and hence higher water uptake, the two SPES membranes exhibited relatively lower values of D as compared to Nafion® 117. The results are discussed in the context of their different microstructures.

Electrochemical characterization of sulfonated poly(arylene ether sulfone) (S-PES) cation-exchange membranes

Sulfonated poly(arylene ether sulfone) (S-PES) cation-exchange membranes with various degrees of the sulfonation were prepared via direct polymerization and characterized in terms of the electrochemical properties, including the surface heterogeneity and the current–voltage ( I– V) relation. The S-PES membranes exhibited moderate swelling properties and ion-exchange capacities (IECs) for electro-membrane applications. Moreover, the membranes with the mole ratio of sulfonated monomers of over 40% showed excellent electrochemical properties. The electrical resistances were below 1.0 Ω cm 2 in a 0.5 mol dm −3 NaCl and the ionic permselectivities were comparable to those of commercial membranes. The fraction of conducting regions, ε, on the membrane surface was evaluated through a chronopotentiometry. The ε values of the S-PES membranes were higher than those of the sulfonated poly(arylene ether sulfone) membranes prepared via conventional post-sulfonation route, leading to a low electrical resistance and a high ionic permselectivity. Considering the mechanical properties, the S-PES membrane with the mole ratio of sulfonated monomers of 40% was found to be very suitable for electro-membrane applications.

SYNTHESIS, CHARACTERIZATION, AND PERFORMANCE OF SULFONATED POLYETHERSULFONE NANOFILTRATION MEMBRANES

ABSTRACT TGA/DTA data. Membranes were prepared from sulfonated polymer and performance characteristics in terms of permeate flux and solute separation are reported. The effects of the casting solution composition on performance of both PES & SPES membranes, effect of feed concentration and separation of different inorganic salts are also included. Separation of multivalent cation (Ca2+) was studied in presence of PAA of different concentration and as a function of pH.