Preparation and characterization of Nafion/SPEEK layered composite membrane and its application in vanadium redox flow battery

In order to reduce the cost of membrane used in vanadium redox flow battery (VRB) system while keeping its chemical stability, Nafion/sulfonated poly(ether ether ketone) (SPEEK) layered composite membrane (N/S membrane) consisting of a thin layer of recast Nafion membrane and a layer of SPEEK membrane were prepared by chemical crosslink the sulfonic acid groups of different ionomer membranes. Scanning electron microscopy (SEM) and IR spectra analysis of the membrane showed that Nafion layer was successfully deposited on the SPEEK membrane surface and an integral layered membrane structure was formed. The area resistance and permeability of vanadium ions of membrane were also measured. It was found that N/S membrane have a very low permeability of vanadium ions accompanied by a little higher area resistance compared with Nafion membrane. As a result, the VRB single cell with N/S membrane exhibited higher coulombic efficiency and lower voltage efficiency compared with VRB single cell with Nafion membrane. Although N/S membrane delivered relatively lower energy efficiency compared with Nafion membrane, its good chemical stability and low cost make it a suitable substitute for Nafion membrane used in VRB system.     

Preparation and characterization of sulfonated polyimide/TiO2 composite membrane for vanadium redox flow battery

A sulfonated polyimide (SPI)/TiO₂ composite membrane was fabricated by a blend way to improve its performance in vanadium redox flow battery (VRB). Both EDS and XRD results verify the successful preparation of the SPI/TiO₂ composite membrane. The surface SEM image shows its homogeneous structure. TG analysis identifies its thermal stability. The SPI/TiO₂ composite membrane possesses much lower permeability of VO²⁺ ions (2.02?×?10^?7 cm² min^?1) and favorable proton conductivity (3.12?×?10^?2 S cm^?1). The VRB single cell with SPI/TiO₂ composite membrane shows higher coulombic efficiency (93.80–98.00 %) and energy efficiency (83.20–67.61 %) at the current density ranged from 20 to 80 mA cm^?2 compared with that with Nafion 117 membrane. And the operational stability of the as-prepared composite membrane is good after 50 times of cycling tests. Therefore, the low-cost SPI/TiO₂ composite membrane with excellent battery performance exhibits a great potential for application in VRB.     

全钒液流电池碳电极材料的研究进展

近年来,全钒液流电池作为一种大规模储能装置,其电极材料得到了广泛的研究,并且获得了一定的进展.本文简述了全钒液流电池对电极材料的要求,综述了其电极材料的研究进展,重点介绍了碳电极及其改性方面的工作,并对其电极材料的发展趋势进行了展望.     

Preparation and characterization of quaternized poly (2,2,2‐trifluoroethyl methacrylate‐co‐N‐vinylimidazole) membrane for vanadium redox flow battery

Aiming to develop a suitable ion exchange membrane for vanadium redox flow battery (VRB), a new kind of imidazolium salt type anion exchange membrane based on the copolymer of N‐vinylimidazole and 2,2,2‐trifluoroethyl methacrylate has been prepared. The membrane is characterized by means of water uptake, ion‐exchange capacity, ionic conductivity, and thermal stability. Furthermore, a VRB with this membrane is assembled, and the performance of such VRB is evaluated. The permeability experiments show that this membrane has reasonable low permeability of vanadium ions. The coulombic efficiency (CE) and energy efficiency (EE) of VRB with the synthesized membrane are 99.5% and 75.0%, whereas the CE and EE of the VRB with Nafion® 117 membrane are 82.6% and 72.6%, respectively. The synthesized membrane shows good chemical stability in VRB via more than 4000 cycles test. Therefore, this membrane shows good applicable potential in VRB. Copyright © 2012 John Wiley & Sons, Ltd.     

表面修饰模式对Nafion离子选择性影响及在VRFB中的应用

本文采用壳聚糖-磷钨酸层对Nafion膜表面分别进行单面和双面修饰改性,研究了修饰模式对Nafion膜钒离子渗透率、电导率及离子选择性的影响. 结果表明,单面、双面修饰改性均会使Nafion膜的钒离子渗透率显著降低,最高降幅分别达到89.9% (单面修饰) 和92.7% (双面修饰);单面、双面修饰改性均会使Nafion膜的电导率下降,但存在明显差异,在相同修饰厚度条件下,双面修饰改性对Nafion膜电导率的影响比单面修饰改性更小。因此,双面修饰复合膜展示出了比单面修饰复合膜更高的离子选择性,并且在修饰层厚度为17 μm时达到最大值（1.12×10⁵ S•min•cm^-3）. 基于优化的双面修饰Nafion膜的全钒液流电池,在充放电流密度30 mA•cm^-2 时,库伦效率和能量效率分别达到93.5%和 80.7%, 并且在测试时间内展示出良好的循环稳定性.     

Facile synthesis of amphoteric ion exchange membrane by radiation grafting of sodium styrene sulfonate and N,N‐dimethylaminoethyl methacrylate for vanadium redox flow battery

Sodium styrene sulfonate (SSS) and N,N‐dimethylaminoethyl methacrylate (DMAEMA) are grafted into poly(vinylidene difluoride) (PVDF) film using γ‐radiation techniques. SSS could be co‐grafted successfully with DMAEMA, although it is difficult to be grafted solely into PVDF films. Through subsequent protonation process, an amphoteric ion exchange membrane (AIEM) is synthesized facilely and environmentally benignly. The degree of grafting (DOG) increases with absorbed dose and levels off at 40 kGy. Micro‐FTIR and X‐ray photoelectron spectroscopy analyses confirm the existence of the designed units and quaternization of DMAEMA units in the grafted films. The quaternization and grafting occurring at the same time makes it a unique way to synthesize quaternized AIEM in one step. Finally, an AIEM with a DOG of 43% is assembled in the vanadium redox flow battery (VRFB) system, and the VRFB maintains an open circuit voltage higher than 1.4 V after placed for 85 h, which is much longer than that with Nafion117 membrane. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5194–5202     

Custom-made sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) nanocomposite membranes for vanadium redox flow battery applications

Sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) (SPVDF-co-HFP) based nanocomposite proton exchange membranes (PEM) are fabricated by simple solution casting method using polydopamine coated exfoliated molybdenum disulfide (PDA-MoS₂) nanosheets as an alternative for Nafion® in vanadium redox flow batteries (VRFBs). PDA-MoS₂ is synthesized by the etching of exfoliated MoS₂ nanosheets with dopamine molecule by self-polymerization method. Various characteristic results clearly demonstrated that the incorporated PDA-MoS₂ nanosheets homogeneously distributed into the SPVDF-co-HFP matrix and the presence of NH/NH₂ group electrostatically interacts with SPVDF-co-HFP to form a strong acid-base pair and thus enhances the proton transport via Grotthuss type mechanism. Besides, the improvement in surface hydrophilicity provides the vehicle type conduction also. As a result, SPVDF-co-HFP/PM nanocomposite membranes showed higher proton conductivity in comparison with the pristine membrane. Especially SPVDF-co-HFP/PM-1 membrane demonstrated the excellent proton conductivity of 5.24 × 10⁻³ Scm⁻¹ at 25 °C, lower vanadium-ion permeability of 1.05 × 10⁻⁸ cm²min⁻¹ and highest membrane selectivity of 49.9 × 10⁴ Scm⁻³min. On the other hand, vanadium-ion stability of the membrane increased by adding the PD-MoS₂ content is attributed to their strong electrostatic attraction towards the polymer matrix. Overall results suggested that the SPVDF-co-HFP/PM-1 nanocomposite membrane is found to be a better alternative for commercially costly Nafion in VRFB applications.     

Study on stabilities and electrochemical behavior of V(V) electrolyte with acid additives for vanadium redox flow battery

Several acid compounds have been employed as additives of the V(V) electrolyte for vanadium redox flow battery (VRB) to improve its stability and electrochemical activity. Stability of the V(V) electrolyte with and without additives was investigated with ex-situ heating/cooling treatment at a wide temperature range of −5 °C to 60 °C. It was observed that methanesulfonic acid, boric acid, hydrochloric acid, trifluoroacetic acid, polyacrylic acid, oxalic acid, methacrylic acid and phosphotungstic acid could improve the stability of the V(V) electrolyte at a certain range of temperature. Their electrochemical behaviors in the V(V) electrolyte were further studied by cyclic voltammetry (CV), steady state polarization and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical activity, including the reversibility of electrode reaction, the diffusivity of V(V) species, the polarization resistance and the flexibility of charge transfer for the V(V) electrolyte with these additives were all improved compared with the pristine solution.     

Preparation of cation exchange membrane as a separator for the all-vanadium redox flow battery

Chlorosulfonated homogeneous polyethylene (PE) dense film (PE-X) and asymmetric membrane (MH-X) were tested as separators for the all-vanadium redox flow battery. The membranes are prepared by the vapour phase chlorosulfonation of the PE film. The measured lowest resistivites equilibrated in 2 M KCl aqueous solution were 0.27 Ω cm² and 0.96 Ω cm², respectively, for PE-X (with thickness 20 μm) and for MH-X (with PE-layer 20 μm). The area resistivities of the membranes as separators in the all-vanadium redox flow battery were obtained. At a charge-discharge current density 633 A/m², these values were 3.09 Ω cm² and 3.46 Ω cm², respectively, for charge and discharge PE-X, and were 3.26 Ω cm² and 8.30 Ω cm², respectively, for charge and discharge MH-X.     

Sulfonated poly(phthalazinone ether sulfone) membrane as a separator of vanadium redox flow battery

To develop a novel and low-cost membrane as a separator of vanadium redox flow battery, sulfonated poly(phthalazinone ether sulfone) (SPPES) was prepared by sulfonating PPES with fuming sulfuric acid. By testing the sulfonation degree, intrinsic viscosity, and solubility of SPPES, the results showed that sulfonated polymers had higher intrinsic viscosities and excellent solubility in most polar solvents. IR analysis revealed that the –SO₃H group was successfully attached to SPPES backbone. DSC and TG results showed that SPPES exhibited higher T _g than that of PPES, and T _d at the first weight loss of SPPES was about 300?°C. The SPPES membrane (SP-02) showed a dramatic reduction in crossover of vanadium ions across the membrane compared with that of the Nafion membrane. Cell tests identified that VRB with the SPPES membrane exhibited a lower self-discharge rate, higher coulombic efficiency (92.82%), and higher energy efficiency (67.58%) compared with the Nafion system. Furthermore, cycling tests indicated that the single cell with SPPES membrane exhibited a stable performance during 100?cycles.     

Use of block copolymer as compatibilizer in polyimide/zeolite composite membranes

In this work, we introduced a diblock copolymer (dBC), i.e., polystyrene‐b‐poly(hydroxyl ethyl acrylate) (PS‐b‐PHEA) as a compatibilizer to enhance interfacial adhesion between PI and zeolite in PI/Zeolite/dBC (1/0.1/0.05 wt%) membrane for gas separation. FT‐IR spectroscopy showed the formation of hydrogen bonding interactions of the carbonyl and the hydroxyl in dBC with both PI and zeolite. The differential scanning calorimeter (DSC) study showed that the glass transition temperature (T_g) of PI increased upon the introduction of dBC, indicating specific interactions in the mixed matrix membranes. The gas permeabilities of H₂, N₂, O₂, and CO₂ through PI/zeolite 5A/dBC membranes were reduced but the permselectivity were increased compared to neat PI membrane. Copyright © 2009 John Wiley & Sons, Ltd.     

Suppression mechanism of the self-discharge reaction in nickel-metal hydride batteries using a sulfonated polyolefin separator

The suppression mechanism of the self-discharge reaction in nickel-metal hydride batteries using a sulfonated polyolefin separator was investigated with sealed-type AA size cells. The experimental results indicate that a sulfonated polyolefin separator effectively suppresses the self-discharge reaction in nickel-metal hydride batteries by trapping nitrogen-containing redox shuttle substances. It is also found that a sulfonated polyolefin separator traps the shuttle substances as gaseous ammonia. In the experiment examining the influence of the amount of the shuttle substances on the self-discharge, the starting point of the self-discharge agreed well with the point at which the nitrogen adsorption capacity of a sulfonated polyolefin separator reached its maximum.     

不同磺化度下的磺化聚醚醚酮对全钒储能液流电池性质影响的研究

本文报道了采用浓硫酸作为磺化剂,成功合成了不同磺化度下的聚醚醚酮(PEEK)膜,并深入研究了磺化条件包括磺化时间和磺化剂的用量对所获薄膜性能的影响,获得了在不同磺化度（DS）下SPPEK膜的离子交换容,含水率,机械性能,质子电导率等参数,特别测定了在全钒液流电池工作条件下钒离子(Ⅳ)渗透率,首次为该类液流储能电池使用价廉质优的质子交换膜提供了基础实验数据。室温条件下的实验结果如下：1）磺化12小时后,膜的磺化度46%,含水量为28%,钒离子(Ⅳ)选择性最佳（钒离子渗透率为1.2×10-7 cm2/min-1,是Nafion117 (2.9×10-6 cm2/min-1)的1/24）,其质子电导率只有0.02 S/cm;2）磺化96小时其磺化度达79%的膜,质子电导率达0.16 S/cm,是Nafion117 (0.10S/cm) 的1.6倍, 但其机械性能最差;3）与Nafion117膜相比,磺化在36到48小时的SPPEK膜其机械力学性能好,薄膜的钒离子渗透率、离子交换容IEC、质子导电率和含水率高,且对钒离子的选择性佳,尤其价格仅为Nafion膜的1/13,是理想的Nafion膜的代替物,可望直接应用于全钒氧化还原液流（VRB）电池中。本文还讨论了磺化时间和不同磺化剂量对膜的性质的影响。     

High modulus polyimide/polyimide molecular composite films that utilize acetylene unit as a crosslink site

Polyimide/polyimide molecular composite (MC) films comprised of a rigid polyimide derived from biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) and a flexible polyimide derived from BPDA and bis (3,3'-diaminodiphenyl) acetylene (intA) and/or oxydianiline (ODA) were prepared by blending the polyamic acid solutions in 7 : 3 weight ratio, and then imidizing the blend films. Acetylene content in the flexible polyimide backbone was controlled by the ratio of intA and ODA. Cold-drawing of the blend polyamic acid films, followed by imidization, gives high modulus polyimide/polyimide MC films. The modulus of the MC films increased almost linearly with the draw ratio, reaching 25.5 GPa for the 40% drawn film. Acetylene groups in the flexible polyimide can be thermally cured to crosslink. The onset of exotherm appeared at 340°C on DSC, reaching maximum at 398°C. After the thermal crosslinking, the MC films maintained the high modulus, though elongation became small. Taking advantage of the crosslinkable acetylene units, two MC films were laminated and processed at 400°C for 20 min under 100 kg/cm² to give a good-quality laminate film. The interface of the two films was strongly bonded through the crosslinking of acetylene groups. Laminate films maintained the high modulus afforded by the cold-drawing. © 1994 John Wiley & Sons, Inc.     

The effect of crosslinked networks with poly(ethylene glycol) on sulfonated polyimide for polymer electrolyte membrane fuel cell

To investigate the effect of crosslinking by a hydrophilic group on a sulfonated polyimide electrolyte membrane, sulfonated polyimide end‐capped with maleic anhydride was synthesized using 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl, 2,2′‐disulfonic acid, 2‐bis [4‐(4‐aminophenoxy)phenyl] hexafluropropane and maleic anhydride. The sulfonated polyimides end‐capped with maleic anhydride were self‐crosslinked or crosslinked with poly(ethylene glycol) diacrylate. A series of the crosslinked sulfonated polyimides having various ratios of sulfonated polyimide and poly(ethylene glycol) diacrylate were prepared and compared with uncrosslinked and self‐crosslinked sulfonated polyimides. The synthesized sulfonated polyimide films were characterized for FTIR spectrum, thermal stability, ion exchange capacity, water uptake, hydrolytic stability, morphological structure, and proton conductivity. The formation of sulfonated polyimide was confirmed in FTIR spectrum. Thermal stability was good for all the sulfonated polyimides that exhibited a three‐step degradation pattern. Ion exchange capacity was the same for both the uncrosslinked and the self‐crosslinked sulfonated polyimides (1.30 mEq/g). When the crosslinked sulfonated polyimides with poly(ethylene glycol) were compared, the ion exchange capacity was decreased as 1.27 > 1.25 > 1.23 mEq/g and water uptake was increased as 23.8 < 24.0 < 24.3% with the increase in poly(ethylene glycol) diacrylate content. All the crosslinked sulfonated polyimides with poly(ethylene glycol) diacrylate were stable for over 200 h at 80 °C in deionized water. Morphological structure and mean intermolecular distance were obtained by WAXD. Proton conductivities were measured at 30, 50, 70, and 90 °C. The proton conductivity of the crosslinked sulfonated polyimides with poly(ethylene glycol) diacrylate increased with the increase in poly(ethylene glycol) diacrylate content despite the fact that the ion exchange capacity was decreased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1455–1464, 2005     

全钒氧化还原液流电池Nafion/SiO_2复合膜的研究

采用溶胶-凝胶法制备Nafion117/SiO2复合膜.工艺研究表明:复合膜制备过程中,加入的MeOH与TEOS比例基本不影响复合膜的阻钒性能.但如以水解时间10 min,水解完成后自然晾干24 h制备的复合膜,则其VO2+的渗透率最低,为4.27×10-9cm2/s,比Nafion117膜的渗透率降低了52倍.SEM测试表明,经自然晾干的复合膜,其中SiO2晶粒长大,并填充了Nafion膜中大部分的孔洞.以其作隔膜组装全钒氧化还原液流电池(单电池),测试表明膜掺杂后电池的电力效率提高2.7%.     

Addition of SiO2 to the operation of a polyimide cathode in a sodium battery

The effect of the addition of SiO₂ nanoparticles on the properties of a polyimide cathode was explored by CV, XPS, and galvanostatic cycling methods. The capacity and average cycling potential of the cell increased in the presence of SiO₂. By quantum chemical modeling, it was shown that SiO₂ nanoparticles served as a framework for polyimide, which retained its fixed structure upon metalation with sodium.     

Crosslinking of anion exchange membrane by accelerated electron radiation as a separator for the all-vanadium redox flow battery

The commercially available anion exchange membrane was crosslinked by accelerated electron radiation, and the performance of the all-vanadium redox flow battery using the crosslinked membrane was measured. The current efficiency of the cell using the crosslinked membrane was higher than that of the cell using the non-crosslinked membrane. The all-vanadium redox flow battery which used the crosslinked membrane (at a dose of 5 Mrad) had better performance with a current efficiency of 93.5%, voltage efficiency of 87.7% and overall energy efficiency of 82%. The overall energy efficiency over of 80% which was achieved for the all-vanadium redox flow battery makes it one of the most promising alternative energy storage systems currently under development. The performance properties of the cell using the crosslinked membrane (at a dose of 5 Mrad) did not change over several cycles showing good chemical stability of the membrane.     

Preliminary evaluation of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid composite membranes for direct methanol fuel cell applications

A series of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid (SPEEK/MEA/AA) composite membranes are prepared and investigated to assess their possibility as proton exchange membranes in direct methanol fuel cells (DMFCs). A preliminary evaluation shows that introducing MEA and AA into SPEEK matrix decreases the thermal stability of membrane. However, the degradation temperatures are still above 260 °C, satisfying the requirement for fuel cell operation. Compared with the pure SPEEK membrane, the composite membranes exhibit not only lower water uptake and swelling ratios but also better mechanical property and oxidative stability. Noticeably, the methanol diffusion coefficient of the composite membranes decrease significantly from 3.15 × 10^?6 to 0.76 × 10^?6 cm²/s with increasing MEA and AA content, accompanied by only a small sacrifice in proton conductivity. Although both the methanol diffusion coefficient and the proton conductivity of composite membranes are lower than those of pure SPEEK and Nafion® 117 membranes, their selectivity (conductivity/methanol diffusion coefficient) are higher. In addition, the composite membranes show excellent stability in aqueous methanol solution. The good thermal and chemical stability, low swelling ratio, excellent mechanical property, low methanol diffusion coefficient, and high selectivity make the use of these composite membranes in DMFCs quite attractive. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2871–2879, 2007     

End-group cross-linked membranes based on highly sulfonated poly(arylene ether sulfone) with vinyl functionalized graphene oxide as a cross-linker and a filler for proton exchange membrane fuel cell application

High-performance end-group cross-linked sulfonated poly(arylene ether sulfone) (SPAES) membranes are developed using thiolate-terminated SPAES with very high degree of sulfonation (DS) such as 90 mol% (SK-SPAES90) and vinyl functionalized graphene oxide (VGO) as a cross-linker and a filler through the thiol-Michael addition reaction. Since free-standing membranes for fuel cell application could not be prepared using the water soluble and highly proton conductive SPAES with high DS of 90 mol%, cross-linked SPAES90 membranes are intentionally prepared. The cross-linked membranes are found to have good physicochemical properties with excellent proton conductivity that can be applied for the proton exchange membrane. In particular, the cross-linked SPAES90 membrane prepared using 1.0 wt% of VGO exhibits better dimensional stability than a SPAES70 membrane from the linear SPAES with DS of 70 mol% and the proton conductivities of this membrane are larger than those of Nafion 211 at 80 °C under different relative humidity conditions (40%-95%).