Crosslinked poly(arylene ether sulfone) block copolymers containing quinoxaline crosslinkage and pendant butanesulfonic acid groups as proton exchange membranes

Crosslinkable poly (arylene ether sulfone) block copolymers (bSPAES (x/y)) containing pendant butanesulfonic acid and ethanedione groups were prepared from a new side-chain difluoro aromatic monomer 1-(2,6-difluorophenyl)-2-(3,5-dimethoxyphenyl)-1,2-ethanedione via block copolycondensation, demethylation, and further nucleophilic substitution of 1,4-butane sultone. Meanwhile, quinoxaline-based crosslinked block copolymers (C-bSPAES (x/y)) were obtained via cyclocondensation. The corresponding block copolymer membranes have high mechanical properties and anisotropic membrane swelling for either crosslinked or uncrosslinked ones. bSPAES (5/10) with ion exchange capacity (IEC) of 2.05 mequiv. g⁻¹ has low water uptake (WU) of 59.1% at 80 °C but relatively high conductivity of 225 mS cm⁻¹, which is ascribed to its good microphase separation. Meanwhile, the crosslinked C-bSPAES (5/10) with IEC of 1.76 mequiv. g⁻¹ exhibits a decreased WU by half, an improved oxidative stability by 200% and a reduced membrane swelling by 40% than the uncrosslinked bSPAES (5/10). The results suggest that quinoxaline-based crosslinking can obviously improve properties of bSPAES (x/y). In addition, even though maximum power density of C-bSPAES (5/10) is lower than that of Nafion 212, C-bSPAES (5/10) still has an acceptable good single-cell performance, indicating a possible fuel cell application.     

Synthesis and characterization of sulfonated poly(ether sulfone) copolymer membranes for fuel cell applications

Sulfonated poly(ether sulfone) copolymers (PESs) are synthesized using hydroquinone 2-potassium sulfonate (HPS) with other monomers (bisphenol A and 4-fluorophenyl sulfone). A series of PESs with different mol% of hydrophilic group is prepared by changing the mole ratio of HPS in the polymerization reaction. The chemical structure and thermal stability of the polymers are characterized by using ¹H NMR, FT-IR and TGA techniques. The PES 60 membrane, which has 60 mol% of HPS unit in the polymer backbone, has a proton conductivity of 0.091 S cm⁻¹ and good insolubility in boiling water. The TGA showed that PES 60 is stable up to 272 °C with a char yield of about 29% at 900 °C under a nitrogen atmosphere. To investigate single-cell performance, a catalyst-coated PES 60 membrane is used together with hydrogen and oxygen as the fuel and the oxidant, respectively. Cell performance is enhanced by increasing the temperature. A current density of 1400 mA cm⁻² at 0.60 V is obtained at 70 °C.     

Sulfonated poly(ether ether ketone)-based composite membrane for polymer electrolyte membrane fuel cells

The solid proton conductor zirconium phosphate sulfophenylenphosphonate of composition Zr(HPO₄)_0.65(SPP)_1.35 where SPP denotes metasulfophenylenphosphonate was prepared in the amorphous gel form in dimethyl formamide (DMF) and characterized by ³¹P NMR. The composite membranes of SPEEK up to 50 wt.% of zirconium phosphate sulfophenylenphosphonate content were prepared by introducing the solid proton conductor from the gel. The composite membranes were characterized using FT-IR, powder X-ray diffraction, SEM, DSC/TGA. The proton conductivity of the membranes was measured under 100% relative humidity up to 70 °C. The composite membranes had better thermal stability when compared with that of SPEEK. A three-fold increase in proton conductivity at 70 °C was observed for the composite membrane with 50 wt.% of solid proton conductor. Furthermore, the conductivity results imply that a critical percentage of proton conductor is needed to establish conduction pathways in the polymer matrix.     

PVDF-g-PSSA and Al2O3 composite proton exchange membranes

Poly(vinylidene fluoride) grafted polystyrene sulfonated acid (PVDF-g-PSSA) membranes doped with different amount of Al₂O₃ (PVDF/Al₂O₃-g-PSSA) were prepared based on the solution-grafting technique. The microstructure of the membranes was characterized by IR-spectra and scanning electron microscope (SEM). The thermal stability was measured by thermal gravity analysis (TGA). The degree of grafting, water-uptake, proton conductivity and methanol permeability were measured. The results show that the PVDF-g-PSSA membrane doped with 10% Al₂O₃ has a lower methanol permeability of 6.6 × 10⁻⁸ cm² s⁻¹, which is almost one-fortieth of that of Nafion-117, and this membrane has moderate proton conductivity of 4.5 × 10⁻² S cm⁻¹. Tests on cells show that a DMFC with the PVDF/10%Al₂O₃-g-PSSA has a better performance than Nafion-117. Although Al₂O₃ has some influence on the stability of the membrane, it can still be used in direct methanol fuel cells in the moderate temperature.     

Influence of composition and acid treatment on proton conduction of composite polybenzimidazole membranes

Inorganic/organic composite membranes formed by polybenzimidazole, silicotungstic acid and silica with different ratio between them have been prepared and characterized before and after treatment in phosphoric acid in order to evaluate the influence of composition and acid treatment on some main characteristics of the membranes. In particular the proton conductivity, the mechanical stability and the structural characteristics of the membranes were evaluated. Silica behaved as a support on which the heteropolyacid remained blocked in finely dispersed state and as an adsorbent for water, thus determining a beneficial effect on proton conduction. The membrane with 50 wt.% of SiWA–SiO₂/PBI, mechanically stable, gave proton conductivity of 1.2×10⁻³ S cm⁻¹ at 160°C and 100% relative humidity. After treatment with phosphoric acid the proton conductivity of membranes increased to 2.23×10⁻³ S cm⁻¹ under the same test conditions. All the materials prepared had amorphous structure.     

Characterization of polymer electrolytes based on poly(dimethyl siloxane-co-ethylene oxide)

The usefulness of poly(dimethyl siloxane-co-ethylene oxide) (P(DMS-co-EO)) copolymer as an ion conducting matrix was investigated. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry. The glass transition temperature (T_g) and degree of crystallization as a function of salt concentration were examined by differential scanning calorimetry. Ionic conductivities as high as 2.6×10⁻⁴ S cm⁻¹ were determined at 25 °C for copolymers films with 5 wt.% LiClO₄. These same films had an electrochemical stability window of 5 V. The pseudo-activation energy as a function of salt concentration was obtained using the Vogel–Tamman–Fulcher (VTF) equation.     

Improved proton conduction of sulfonated poly (ether ether ketone) membrane by sulfonated covalent organic framework nanosheets

A type of sulfonated covalent organic framework nanosheets (TpPa-SO₃H) was synthesized via interfacial polymerization and incorporated into sulfonated poly (ether ether ketone) (SPEEK) matrix to prepare proton exchange membranes (PEMs). The densely and orderly arranged sulfonic acid groups in the rigid skeleton of the TpPa-SO₃H nanosheets, together with their high-aspect-ratio and well-defined porous structure provide proton-conducting highways in the membrane. The doping of TpPa-SO₃H nanosheets led to an increased ion exchange capacity up to 2.34 mmol g^?1 but a 2-folds reduced swelling ratio, remarkably mitigating the trade-off between high IEC and excessive swelling ratio. Based on the high IEC and orderly arranged proton-conducting sites, the SPEEK/TpPa–SO₃H–5 membrane exhibited the maximum proton conductivity of 0.346 S cm^?1 at 80 °C, 1.91-folds higher than the pristine SPEEK membrane. The mechanical strength of the composite membrane was also improved by 2.05-folds–74.5 MPa. The single H₂/O₂ fuel cell using the SPEEK/TpPa–SO₃H–5 membrane presented favorable performance with an open voltage of 1.01 V and a power density of 86.54 mW cm^?2.     

A new class of alkaline polymer gel electrolyte for carbon aerogel supercapacitors

A carbon aerogel supercapacitor has been fabricated with an alkaline polymer gel electrolyte. The electrolyte, which also acts as a separator, has a thickness of 3 mm and a conductivity of around 10⁻² S cm⁻¹ at room temperature. The capacitor is characterized by means of cyclic voltammetry, impedance spectroscopy, and galvanostatic cycling. A specific capacitance of 9 F g⁻¹ is shown by cyclic voltammetry.     

Inorganic proton-conducting gel glass/porous alumina nanocomposite

A novel fast proton-conducting silicophosphate-HClO₄ (SiP-HClO₄) gel glass and SiP-HClO₄–alumina composite are successfully fabricated. The fabricated inorganic composites show good thermal stability and stable conductivity up to 140 °C, which indicates a high proton conductivity of over 2.6 × 10⁻² S cm⁻¹. The high conductivity of the composites is attributed to the fast proton-conducting property of the three-dimensional SiP-HClO₄ gel glass network which contains both trapped acid ions (ClO₄⁻) as a proton donor and strongly hydrogen-bonded hydroxyl groups combined to P–O–Si bonds as proton conduction paths.     

Proton conducting behavior of a novel polymeric gel membrane based on poly(ethylene oxide)-grafted-poly(methacrylate)

A novel proton conducting polymeric gel membrane that consists of poly(ethylene oxide)-grafted-poly(methacrylate) (PEO-PMA) with poly(ethylene glycol) dimethyl ether (PEGDE) as a plasticizer doped with aqueous phosphoric acid (H₃PO₄) has been prepared and its physicochemical properties were studied in detail. The ionic conductivity was dependent much on the concentration of H₃PO₄, the immersion time, and content of the plasticizer. This type of proton conducting polymeric gels shares not only good mechanical properties but also thermal stability. Maximum conductivities up to 2.6×10⁻² S cm⁻¹ at room temperature (25 °C) and 2.8×10⁻² S cm⁻¹ at 70 °C were obtained for the composition of the polymer matrix to the plasticizer as 35/65 (in mass) after the H₃PO₄ doping from the aqueous solution with 2.93 mol l⁻¹. FT-IR spectra showed that these high proton conductivities are attributed to the presence of excesses free H₃PO₄ in the polymeric gel in addition to the hydrogen-bonded H₃PO₄ to the polymer matrix.     

Optimization of ethanol production from sweet sorghum (Sorghum bicolor) juice using response surface methodology

Sweet sorghum juice was fermented into ethanol using Saccharomyces cerevisiae (ATCC 24858). Factorial experimental design, regression analysis and response surface method were used to analyze the effects of the process parameters including juice solid concentration from 6.5 to 26% (by mass), yeast load from 0.5 g L⁻¹ to 2 g L⁻¹ and fermentation temperature from 30 °C to 40 °C on the ethanol yield, final ethanol concentration and fermentation kinetics. The fermentation temperature, which had no significant effect on the ethanol yield and final ethanol concentration, could be set at 35 °C to achieve the maximum fermentation rate. The yeast load, which had no significant effect on the final ethanol concentration and fermentation rate, could be set at 1 g L⁻¹ to achieve the maximum ethanol yield. The juice solid concentration had significant inverse effects on the ethanol yield and final ethanol concentration but a slight effect on the fermentation rate. The raw juice at a solid concentration of 13% (by mass) could be directly used during fermentation. At the fermentation temperature of 35 °C, yeast solid concentration of 1 g L⁻¹ and juice solid concentration of 13%, the predicted ethanol yield was 101.1% and the predicted final ethanol concentration was 49.48 g L⁻¹ after 72 h fermentation. Under this fermentation condition, the modified Gompertz's equation could be used to predict the fermentation kinetics. The predicted maximum ethanol generation rate was 2.37 g L⁻¹ h⁻¹.     

Effects of addition of TiO2 nanoparticles on mechanical properties and ionic conductivity of solvent-free polymer electrolytes based on porous P(VdF-HFP)/P(EO-EC) membranes

To enhance the performance (i.e., mechanical properties and ionic conductivity) of pore-filling polymer electrolytes, titanium dioxide (TiO₂) nanoparticles are added to both a porous membrane and its included viscous electrolyte, poly(ethylene oxide-co-ethylene carbonate) copolymer (P(EO-EC)). A porous membrane with 10 wt.% TiO₂ shows better performance (e.g., homogeneous distribution, high uptake, and good mechanical properties) than the others studied and is therefore chosen as the matrix to prepare polymer electrolytes. A maximum conductivity of 5.1 × 10⁻⁵ S cm⁻¹ at 25 °C is obtained for a polymer electrolyte containing 1.5 wt.% TiO₂ in a viscous electrolyte, compared with 3.2 × 10⁻⁵ S cm⁻¹ for a polymer electrolyte without TiO₂. The glass transition temperature, T_g is lowered by the addition of TiO₂ (up to 1.5 wt.% in a viscous electrolyte) due to interaction between P(EO-EC) and TiO₂, which weakens the interaction between oxide groups of the P(EO-EC) and lithium cations. The overall results indicate that the sample prepared with 10 wt.% TiO₂ for a porous membrane and 1.5 wt.% TiO₂ for a viscous electrolyte is a promising polymer electrolyte for rechargeable lithium batteries.     

Ionic conductance of PDMAEMA/PEO polymeric electrolyte containing lithium salt mixed with plasticizer

Novel plasticized polymer electrolytes were synthesized with poly(N,N-dimethylamino-ethyl-methacrylate) (PDMAEMA), polyethylene oxide (PEO), LiTFSI as a salt, tetraethylene glycol dimethyl ether (tetraglyme), EC/PC and DEP as plasticizers. The ionic conductivity of various compositions of polymer electrolytes was investigated as a function of temperature, various concentrations of LiTFSI, plasticizers and various ratio of PDMAEMA/PEO. The ionic conductivity of PDMAEMA/PEO/LiTFSI (1.5 mol kg⁻¹) with DEP as a plasticizer (1.5 × 10⁻⁴ S cm⁻¹) exhibited lower than PDMAEMA/PEO/LiTFSI (1.2 mol kg⁻¹)/tetraglyme (5.24 × 10⁻⁴ S cm⁻¹) and PDMAEMA/PEO/LiTFSI (1.5 mol kg⁻¹)/EC + PC (2.1 × 10⁻⁴ S cm⁻¹). As increasing the PDMAEMA concentration up to 13.3%, the ionic conductivity was decreased rapidly. As increasing the PDMAEMA concentration the ionic conductivity was decreased due to high viscosity and some interactions reducing ion pairing. These plasticized polymer electrolytes were characterized by impedance spectroscopy and DSC.     

Improving the proton conductivity of sulfonated poly (ether ether ketone) membranes by incorporating a crystalline nanoassembly of trimesic acid and melamine

A novel proton exchange membrane was synthesized by embedding a crystalline which was nano-assembled through trimesic acid and melamine (TMA·M) into the matrix of the sulfonated poly (ether ether ketone) (SPEEK) to enhance the proton conductivity of the SPEEK membrane. Fourier transform infrared indicated that hydrogen bonds existed between SPEEK and TMA·M. XRD and SEM indicated that TMA·M was uniformly distributed within the matrix of SPEEK, and no phase separation occurred. Thermogravimetric analysis showed that this membrane could be applied as high temperature proton exchange membrane until 250 °C. The dimensional stability and mechanical properties of the composite membranes showed that the performance of the composite membranes is superior to that of the pristine SPEEK. Since TMA·M had a highly ordered nanostructure, and contained lots of hydrogen bonds and water molecules, the proton conductivity of the SPEEK/TMA·M-20% reached 0.00513 S cm⁻¹ at 25 °C and relative humidity 100%, which was 3 times more than the pristine SPEEK membrane, and achieved 0.00994 S cm⁻¹ at 120 °C.     

Lithium ion and electronic conductivity in 3-(oligoethylene oxide)thiophene comb-like polymers

The Li-ion and electronic conductivities of a series of p-doped poly(thiophene)s with oligo-ethylene oxide side chains have been determined at room temperature as functions of side-chain length and concentration of LiOTf dissolved in the polymers in order to assess their utility as binders in Li-ion batteries. The lithium triflate concentration was varied from 0.23 to 2.26 mmol LiOTf/g –C₂H₄O– (100 O:Li to 10 O:Li), and the concentration of dissociated Li⁺ was determined from the IR spectra of the polymer solutions. The greatest ionic conductivity, 2 × 10⁻⁴ S cm⁻¹, was attained with intermediate concentrations of added salt that corresponded with the greatest degree of LiOTf dissociation. Li-ion mobilities of 5 × 10⁻⁷ cm² (Vs)⁻¹ were measured for poly(thiophene)s (PT) with short oligo(ethylene oxide) side-chains (E_n), PE₂T and PE₃T, whereas the polymers with longer side chains, PE₇T and PE₁₅T, had Li-ion mobilities about an order of magnitude greater, 5 × 10⁻⁶ cm² (Vs)⁻¹. The electronic conductivity of the polymers heavily doped with NOBF₄ was near 0.1 S cm⁻¹ for PE₂T and PE₃T, but was orders of magnitude smaller for the polymers with longer side-chains. Addition of LiOTf caused the electronic conductivity of PE₂T and PE₃T to drop to that of the longer chain polymers whose conductivities were insensitive to the LiOTf concentration.     

Fabrication and properties of hybrid membranes based on salts of heteropolyacid,zirconium phosphate and polyvinyl alcohol

The fabrication and properties of a hybrid membrane based on cesium salt of heteropoly acid, zirconium phosphate and polyvinyl alcohol are described. The fabricated membranes were characterized for their intra molecular interaction, thermal stability, surface morphology, water content and surface-charge properties using Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water uptake and ion-exchange capacity measurements. These membranes showed reduced methanol crossover (for possible application in DMFC) relative to that of Nafion^® 115. At 50% of relative humidity, the protonic conductivity of the hybrid membranes was in the range of 10⁻³ to 10⁻² S cm⁻¹. The feasibility of these hybrid membranes as proton conducting electrolyte in direct methanol fuel cell (DMFC) was investigated and preliminary results are compared with that of Nafion^® 115. A maximum power density of 6 mW cm⁻² with PVA–ZrP–Cs₂STA hybrid membrane was obtained with the cell operated in passive mode at 373 K and atmospheric pressure. Open circuit voltage of the cell operated with hybrid membranes are high compared to that of Nafion^® 115 indicating reduced methanol crossover.     

Effect of ball milling on structural and electrochemical properties of (PEO)nLiX (LiX = LiCF3SO3 and LiBF4) polymer electrolytes

Polymer electrolytes consisting of poly(ethylene oxide) (PEO) and lithium salts, such as LiCF₃SO₃ and LiBF₄ are prepared by the ball-milling method. This is performed at various times (2, 4, 8, 12 h) with ball:sample ratio of 400:1. The electrochemical and thermal characteristics of the electrolytes are evaluated. The structure and morphology of PEO–LiX polymer electrolyte is changed to amorphous and smaller spherulite texture by ball milling. The ionic conductivity of the PEO–LiX polymer electrolytes increases by about one order of magnitude than that of electrolytes prepared without ball milling. Also, the ball milled electrolytes have remarkably higher ionic conductivity at low temperature. Maximum ionic conductivity is found for the PEO–LiX prepared by ball milling for 12 h, viz. 2.52×10⁻⁴ S cm⁻¹ for LiCF₃SO₃ and 4.99×10⁻⁴ S cm⁻¹ for LiBF₄ at 90 °C. The first discharge capacity of Li/S cells increases with increasing ball milling time. (PEO)₁₀LiCF₃SO₃ polymer electrolyte prepared by ball milling show the typical two plateau discharge curves in a Li/S battery. The upper voltage plateau for the polymer electrolyte containing LiBF₄ differs markedly from the typical shape.     

All-solid-state lithium secondary batteries using a layer-structured LiNi0.5Mn0.5O2 cathode material

All-solid-state cells of In/LiNi_0.5Mn_0.5O₂ using a superionic oxysulfide glass with high conductivity at room temperature of 10⁻³ S cm⁻¹ as a solid electrolyte were fabricated and the cell performance was investigated. Although a large irreversible capacity was observed at the 1st cycle, the solid-state cells worked as lithium secondary batteries and exhibited excellent cycling performance after the 2nd cycle; the cells kept charge–discharge capacities around 70 mAh g⁻¹ and its efficiency was almost 100%. This is the first case to confirm that all-solid-state cells using manganese-based layer-structured cathode materials work as lithium secondary batteries.     

Novel organic–inorganic poly (3,4-ethylenedioxythiophene) based nanohybrid materials for rechargeable lithium batteries and supercapacitors

Synthesis and characterization of poly (3,4-ethylenedioxythiophene) (PEDOT) interleaved between the layers of crystalline oxides of V and Mo is discussed with special emphasis on their application potential as electrodes for rechargeable Li batteries and supercapacitors. The expansion of the interlayer spacing of crystalline oxides (for example, V₂O₅ causes expansion from 0.43 to 1.41 nm) is consistent with a random layer stacking structure. These hybrid nanocomposites when coupled with a large-area Li foil electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcarbonate (1:1, v/v), give enhanced discharge capacity compared to pristine oxides. For example a discharge capacity of ∼350 mAh g⁻¹, in the potential range 4.2–2.1 V (versus Li⁺/Li) is obtained for PEDOT–V₂O₅ hybrid which is significantly large compared to that for simple Li-intercalated V₂O_5. The improvement of electrochemical performance compared with that of pristine oxides is attributed to higher electric conductivity, enhanced bi-dimensionality and increased structural disorder. Although these conducting polymer-oxide hybrids delivered more than 300 mAh g⁻¹ in the potential range 1.3–4.3 V, their cycle life needs further improvements to realize their commercial potential. Similarly, the double layer capacitance of MoO₃ increases from ∼40 mF g⁻¹ to ∼300 F g⁻¹ after PEDOT incorporation in the interlayer gap of MoO₃ under similar experimental conditions and the nanocomposite displays intriguing effects with respect to electrochemical Li⁺ insertion. The PEDOT–MoO₃ nanocomposite appears to be a promising electrode material for non-aqueous type supercapacitors.     

Sulfonated poly(ether sulfone) for universal polymer electrolyte fuel cell operations

The performances of the proton exchange membrane fuel cell (PEMFC), direct formic acid fuel cell (DFAFC) and direct methanol fuel cell (DMFC) with sulfonated poly(ether sulfone) membrane are reported. Pt/C was coated on the membrane directly to fabricate a MEA for PEMFC operation. A single cell test was carried out using H₂/air as the fuel and oxidant. A current density of 730 mA cm⁻² at 0.60 V was obtained at 70 °C. Pt–Ru (anode) and Pt (cathode) were coated on the membrane for DMFC operations. It produced 83 mW cm⁻² maximum power density. The sulfonated poly(ether sulfone) membrane was also used for DFAFC operation under several different conditions. It showed good cell performances for several different kinds of polymer electrolyte fuel cell applications.