Evaluation of the chemical stability of some membranes in vanadium solution

The chemical stability of Daramic®, modified Daramic® and several commercial ion exchange membranes was studied in the vanadium redox battery (VRB). The Selemion® CMV membrane showed the lowest chemical stability in the VRB, while Nafion® 112 and New Selemion® (type 2) showed excellent stability. The composite membrane prepared by crosslinking of Daramic® with divinylbenzene (DVB) showed good chemical stability similar to the Selemion® AMV membrane. Sulfonation of the composite membrane and AMV membrane did not improve their stability in the vanadium solution. It was found that the weight loss of the membranes is almost proportional to the conversion of V(v) ions to V(iv) ions in the test solution showing that the chemical degradation is associated with the oxidation of the polymeric membrane material by the V(V) ions in the positive half cell electrolyte. The Nafion® 112 membrane was found to be susceptible to fouling which can be reversed by simply soaking in H2SO4 solution.     

Chemical and mechanical degradation of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

A sulfonated poly(sulfone) (S-Radel^®) membrane with high proton conductivity and low vanadium ion permeability showed high initial performance in a vanadium redox flow battery (VRFB) but suffered mechanical and chemical degradation during charge/discharge cycling. The S-Radel membrane showed different degradation behavior in flow cell cycling and ex-situ vanadium ion immersion tests. When the membrane was immersed in aqueous V⁵⁺ solution, the sample cracked into small pieces, but did not degrade to any measurable extent in V⁴⁺ solution. During charge/discharge cycling in the VRFB cell, the membrane underwent internal delamination, preferentially on the side of the membrane that faced the positive electrode. A vanadium-rich region was observed near the membrane surface that experienced delamination and Raman spectroscopic analysis of the degraded surface indicated a slightly depressed 1026 cm^?1 band corresponding to a loss in the sulfonate SO₂ stretch intensity. Even though the S-Radel membrane underwent severe mechanical damage during the flow cell cycling, significant chemical degradation was not obvious from the spectroscopic analyses. For the VRFB containing an S-Radel membrane, an increase in membrane resistance caused an abnormal voltage depression during the discharge cycle. The reversible increase in membrane resistance and severe mechanical degradation of the membrane during cycling may be attributed to repeated formation and dissolution of particles inside the membrane. The mechanical stresses imposed by the particles coupled with a small amount of chemical degradation of the polymer by V⁵⁺ ions, are likely degradation mechanisms of the S-Radel membrane in VRFBs under high state-of-charge conditions.     

Permeation of vanadium cations through anionic and cationic membranes

The permeability of four commercially available ion-exchange membranes, the cationic Nafion 125 (duPont) and Selemion CMV (Asahi Glass) membranes and the anionic Selemion AMV and DMV membranes, to vanadyl, VO²⁺, and vanadic, VO ₂ ⁺ , ions was studied. The results show that two important variables determine the usefulness of a membrane as a membrane separator in a redox cell. These are selectivity and membrane-electrolyte resistance. Only the DMV membrane was considered to meet the requirements of low permeability to vanadium cations and at the same time permitting H⁺ ions to go through the membrane, thereby providing a very low membrane-electrolyte resistance in the redox fuel cell.     

Conductive carbon-polypropylene composite electrodes for vanadium redox battery

Carbon-polymer composite electrodes have been developed and investigated for application in the vanadium redox flow battery. Electrical, electrochemical, physical and mechanical properties as well as chemical resistance and solution permeability of a wide range of carbon-polymer composite materials were evaluated. Volume resistivities as low as 0.21 cm were achieved with composites based on polypropylene, this being combined with excellent stability. Finally, the performance of a vanadium redox flow cell employing the best composite electrode was evaluated and voltage efficiencies as high as 91 % were achieved at a charge/discharge current density of 20 mA cm^–2.     

Bifunctional redox flow battery: 2. V(III)/V(II)-l-cystine(O2) system

A new bifunctional redox flow battery (BRFB) system, V(III)/V(II)—l-cystine(O₂), was systematically investigated by using different separators. It is shown that during charge, water transfer is significantly restricted with increasing the concentration of HBr when the Nafion 115 cation exchange membrane is employed. The same result can be obtained when the gas diffusion layer (GDL) hot-pressed separator is used. The organic electro-synthesis is directly correlated with the crossover of vanadium. When employing the anion exchange membrane, the electro-synthesis efficiency is over 96% due to a minimal crossover of vanadium. When the GDL hot-pressed separator is applied, the crossover of vanadium and water transfer are noticeably prevented and the electro-synthesis efficiency of over 99% is obtained. Those impurities such as vanadium ions and bromine can be eliminated through the purification of organic electro-synthesized products. The purified product is identified to be l-cysteic acid by IR spectrum. The BRFB shows a favorable discharge performance at a current density of 20 mA cm⁻². Best discharge performance is achieved by using the GDL hot-pressed separator. The coulombic efficiency of 87% and energy efficiency of about 58% can be obtained. The cause of major energy losses is mainly associated with the cross-contamination of anodic and cathodic active electrolytes.     

全钒液流电池用质子传导膜研究进展

全钒液流电池(VRB)作为一种大规模蓄电储能装备,在可再生能源发电和节能技术领域将发挥重要作用。质子传导膜是VRB中的关键材料之一,其作用主要有两方面:传导质子连通电堆内电路;阻止正负极电解液间不同价态钒离子的相互渗透,避免能量损失。质子传导膜性能对电池效率和成本有重要影响。在分析VRB基本原理基础上,阐明质子传导膜需同时满足优良的导电性、阻钒性、稳定性和合理成本等要求。以高分子膜的化学组成与物理结构的演化过程为线索,分别论述三类膜材料,包括Nafion系列膜、非全氟型质子传导膜、纳米尺度孔径的多孔膜。在归纳现有膜材料化学结构、物理性质与电学性能的基础上,阐述高性能质子传导膜的重点研究方向与发展前景。     

基于吸附-扩散机理研究钒离子透膜传质过程(I)——离子膜吸附-扩散模型

钒离子透膜传质是导致钒电池能量损失的关键因素之一,在分析钒离子透膜传质过程的基础上,根据离子交换膜固定电荷理论提出钒离子透膜传质的吸附-扩散模型.由膜内离子Donnan平衡,引入选择性系数研究膜内钒离子吸附过程;考虑膜面浓差电势影响,由Nernst-Planck方程描述膜内钒离子和氢离子交互传质过程,将钒离子透膜扩散过...     

全钒液流电池用磺化聚芴醚酮质子交换膜的制备及性能

质子交换膜(PEM)作为全钒液流电池(VRFB)的核心组件之一,应当解决成本高昂、合成过程复杂等问题,并具备高质子传导率、低钒离子渗透率、高机械强度和优异化学稳定性等关键性能。本文基于四甲基双酚芴单体通过缩聚反应合成了一系列聚芴醚酮化合物PFEKs,再利用溴代反应将苯甲基功能化为溴甲基,接着通过4-羟基苯磺酸钠的SN₂亲核取代制得了一系列不同离子交换容量的磺化聚芴醚酮聚合物(SPFEKs)。通过溶液浇铸法成膜并酸化,得到一系列新型低成本PEMs。该合成路线的原料来源广泛,价格低廉,不涉及危险的磺化反应,易于工业放大。所得膜都具有良好的机械性能和氧化稳定性,其中SPFEK-40膜具有较高的质子传导率及离子选择性、较低的钒离子渗透率及面电阻,综合性能优异。以SPFEK-40膜组装的VRFB在电流密度为80 mA/cm₂^{时的能量效率}(EE)为88.2%,高于以Nafion 212膜组装的VRFB的84.8%。此外,以SPFEK-40膜组装的VRFB在30次循环后放电容量仅衰减至84.3%,远高于以Nafion 212膜组装的VRFB的66.1%。     

Sorption and diffusion of ionic dyes in anionic cellophane membranes

Experimental steady-state permeability studies have been made with non-ionic, anionic and cationic dyes using carboxy cellulose membranes as anionic substrates. The experimental results show that with increasing bulk ionic strength the diffusion velocities of anionic and cationic compounds increase and decrease, respectively. The diffusion behavior of non-ionic compounds is independent of the ionic strength. Empirical relationships have been deduced which fit the permeation data of the anionic compounds. A new concept is introduced which postulates that the diffusion behavior of colons within an anionic membrane is dependent on the basicity of the fixed ionic groups. In substrates with matrix-bound anionic groups of high basicity, such as carboxy cellulose, the permeability behavior is described in terms of a new diffusion mechanism referred to as the “fluctuating” charge mechanism. This concept can provide a semi-quantitative understanding of the different electrostatic obstruction effects which matrix-bound carboxylate and sulfonate groups have on the permeability of colons. The measured permeability of the counter ions is in qualitative agreement with the proposed diffusion model.     

Novel amphoteric ion exchange membranes by blending sulfonated poly(ether ether ketone) with ammonium polyphosphate for vanadium redox flow battery applications

A novel amphoteric ion exchange membrane for vanadium redox flow battery (VRFB) was explored by blending sulfonated poly(ether ether ketone) (SPEEK) and ammonium polyphosphate (APP). The high-stability flame retardant of cross-linked APP with a large number of NH₄⁺ groups was first introduced into SPEEK membrane. It was observed that the addition of APP with special structure could achieve a good balance between proton conductivity and vanadium ions permeability. The abundant NH₄⁺ in APP could block the penetration of vanadium ions by Donnan/Manning exclusion effect and ionic crossing networks due to the ionic bonds between cation and anion groups, and specially a small amount of APP within 5% could remarkably improve the proton conductivity of pristine SPEEK membrane might be ascribed to the unique fast proton transport channels formed by hydrogen bond networks and particular micro-phase separation as a result of interaction between SPEEK and APP. When 5% APP was blended, the SPEEK/APP-5% (S/APP-5%) amphoteric membrane showed a higher selectivity of 20.87 × 10⁴ S min/cm³ (with a good proton conductivity of 0.075 S/cm and a lower VO²⁺ permeability of 3.45 × 10⁻⁷ cm²/ min) and presented better thermal and chemical stability compared to Nafion115 and SPEEK membranes. The VRFB single cell assembled with S/APP-5% amphoteric membrane exhibited more excellent performance than that of Nafion115 and pristine SPEEK membranes, which revealed a higher coulombic efficiency of 96.3%–98.3%, comparable voltage efficiency of 88.4%–78.7% and higher energy efficiency of 85.1%–77.4% from 40 to 80 mA/cm², respectively, and showed relatively good stability of the efficiency up to 50 cycles at 60 mA/cm². The results demonstrated that the designed S/APP amphiprotic membrane of outstanding selectivity, high battery efficiency, and good durability is a prospected VRFB separator.     

Effect of functional group of ferrocene redox substance on the transport properties of newly designed ion exchange membrane prepared from polymer gel

A different newly designed cationic exchange polymer membrane and anionic exchange polymer membrane were introduced, and also the transport properties of these polymeric membranes were investigated in this study. The transport properties of these polymer membranes in contact with ferrocene redox derivatives were estimated by using electrochemical techniques such as cyclicvoltammetry, chronopotentiometry, and chronoamperometry techniques, respectively. The used ferrocene redox substances, which have different functional groups, were (Ferrocenylmethyl) trimethylamonium iodide, FcMA, Ferrocenedimethanol, FcDM, and Ferrocene carboxylic acid, FcCA. It indicated that the performance of a membrane depended on the content of polymer gel, anionic exchange polymer site (20 wt % and 50 wt %) or cationic polymer exchange site (20 wt % and 50 wt %), and the efficiency of the functional groups of cationic and anionic exchange polymer site as well. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Sulfonated poly(ether ether ketone)/s–TiO2 composite membrane for a vanadium redox flow battery

The SPEEK/s-TiO₂ composite membrane was prepared by blending sulfonated poly(ether ether ketone) (SPEEK) and sulfonated titanium dioxide (s-TiO₂) nanoparticles. The important physiochemical parameters such as proton conductivity, water uptake, swelling degree and ion exchange capacity of the composite membrane were measured. The thermal stability and chemical stability were also tested. It was observed that the SPEEK/s-TiO₂ composite membrane exhibited the best selectivity (7.13 × 10⁴ S·min·cm⁻³) accompanying high proton conductivity (0.061 S·cm⁻¹) and low tetravalent vanadium ion (VO²⁺) permeability (8.55 × 10⁻⁷ cm²·min⁻¹) compared with Nafion117, SPEEK and SPEEK/TiO₂ membranes. The battery performance with these membranes was characterized by charge–discharge cycling tests and it was found that the SPEEK/s-TiO₂ composite membrane showed the highest energy efficiency (EE) up to 82.3%, indicating the SPEEK/s-TiO₂ composite membrane is a candidate for vanadium redox flow battery (VRFB) application. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48830.     

Membrane stability studies for vanadium redox cell applications

Accelerated degradation tests of selected membranes were carried out to determine their stability in the fully charged positive electrolyte solution of the vanadium redox battery. Each membrane was soaked in both 1.0 and 0.1 M V(V) solutions for extended periods of time and UV–visible spectroscopy was used to determine the rate of oxidation of the membrane by V(V) to produce V(IV) ions in solution. The membranes were then evaluated for any changes in their resistance, IEC, diffusivity and water transfer properties. FESEM was used to analyse the membranes for physical damage. Different trends were observed in the 1.0 and 0.1 M V(V) electrolytes. Of the membranes studied, Nafion 112E/H⁺ showed the worst stability in the 0.1 M V(V) solution but one of the best stabilities in 1.0 M V(V). The dilute V(V) electrolyte appears to enter the pores of the membrane more readily as the membranes swell significantly in this solution. The 0.1 M V(V) solution therefore causes accelerated deterioration of the membrane performance as a result of physical destruction, chemical modification or a combination of both. The effect is more pronounced in the membranes that have a higher degree of swelling in the vanadium electrolyte.     

Effect of organic additives on positive electrolyte for vanadium redox battery

Fructose, mannitol, glucose, d-sorbitol are explored as additives in electrolyte for vanadium redox battery (VRB), respectively. The effects of additives on electrolyte are studied by cyclic voltammetry (CV), charge–discharge technique, electrochemical impedance spectroscopy (EIS) and Raman spectroscopy. The results indicate that the vanadium redox cell using the electrolyte with the additive of d-sorbitol exhibits the best electrochemical performance (the energy efficiency 81.8%). The EIS results indicate that the electrochemical activity of the electrolyte is improved by adding d-sorbitol, which can be interpreted as the increase of available (–OH) groups providing active sites for electron transfer. The Raman spectra show that VO²⁺ ions take part in forming a complex with the d-sorbitol, which not only improve solubility of V(V) electrolyte, but also provide more activity sites for the V(IV)/V(V) redox reaction.     

全钒液流电池用非氟咪唑型阴离子交换膜的制备

在全钒电池(VFB)用离子交换膜中,阴离子交换膜以其钒离子渗透率低这一主要优势受到了广泛的关注。以N-溴代丁二酰亚胺(NBS)为溴化试剂,2,2'-偶氮二异丁腈(AIBN)为引发剂,对聚苯醚(PPO)的苄甲基溴化;以N-正丁基咪唑为功能化试剂,制备了一种非氟咪唑型聚苯醚阴离子交换膜。研究了不同N-正丁基咪唑功能化程度的阴离子交换膜的离子传导率、离子交换容量(IEC)、含水率、钒离子传递系数等性能,并与N-甲基咪唑功能化的阴离子交换膜做了对比。结果显示,N-正丁基咪唑功能化聚苯醚阴离子交换膜的钒离子传递系数为4.8×10^-9 cm·min^-1,60℃时离子传导率为10.8 mS·cm^-1,且化学稳定性及力学性能优异,具有在钒电池中应用的潜力。     

聚苯乙烯磺酸钠对掺混聚偏氟乙烯阴离子交换膜的改性表征

聚苯乙烯磺酸钠（PSS）因含有强电离作用的负电荷基团（磺酸基团）可以和聚偏氟乙烯（PVDF）一起改性阴离子交换膜,使膜在提高稳定性的前提下,保证其他性能。本实验采用浸润改性法,用PSS浸润改性添加了PVDF的阴离子交换膜。探讨了PSS含量对膜性能的影响,如膜电阻、离子交换容量、含水率和选择透过性。利用红外光谱仪及扫描电子显微镜表征手段对膜表面性质和结构进行了分析。结果表明,当PSS含量增加时,膜面电阻先降低后升高,离子交换容量和含水率升高,离子选择透过性先升高后降低。虽然PVDF的添加使阴离子交换膜除稳定性外的其他性能下降,但PSS的浸润改性弥补了这一缺陷,这使得PSS与PVDF复合改性的阴离子交换膜具有一定的实用价值。     

A super thin polytetrafluoroethylene/sulfonated poly(ether ether ketone) membrane with 91% energy efficiency and high stability for vanadium redox flow battery

In order to further decrease the cost and enhance the durability of sulfonated poly(ether ether ketone) membrane for vanadium redox flow battery, a super thin (40 μm) polytetrafluoroethylene (PTFE)/SPEEK (PS) membrane is prepared. The physico‐chemical properties and single cell performance of PS membranes prepared with different casting solvents including NMP (N‐methyl‐2‐pyrrolidone), DMF (N,N′‐dimethylformamide), and DMAc (N,N′‐dimethylacetamide) have been investigated. Results show that the energy efficiency of VRB with PS/DMF can reach up to 91.2% at the current density of 40 mA cm^?2, which is 11.1% and 6.4% higher than that of the commercial Nafion 212 and pristine SPEEK membrane, respectively. In addition, charge–discharge test over 150 times proves that the PS/DMF membrane possesses high stability and thus it is suitable for VRB application. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43593.     

Application of Psf–PPSS–TPA composite membrane in the all-vanadium redox flow battery

The Psf–PPSS–TPA composite cation exchange membrane consist of Psf(polysulfone)–PPSS (polyphenylenesulfidesulfone) block copolymer with TPA (tungstophosphoric acid) is prepared to apply for a separator in the all-vanadium redox flow battery. The membrane properties such as membrane resistance and ion exchange capacity, and thermal stability are investigated. The prepared Psf–PPSS–TPA composite cation exchange membrane showed higher thermal stability than Nafion117. The lowest membrane resistance of the prepared Psf–PPSS–TPA composite cation exchange membrane measured in 1 M (mol/dm³) H₂SO₄ aqueous solution was 0.94 Ω cm² at 0.5 g of TPA solution. The performance properties of the all-vanadium redox flow battery (V-RFB) using the prepared cation exchange membrane are measured. The electromotive force, open circuit voltage at state of charge (SOC) of 100%, was 1.4 V. This value meets a theoretical electromotive force value of the V-RFB. The measuring cell resistance in charge and discharge at SOC 100% were 0.26 Ω and 0.31 Ω, respectively. The results of the present study suggest that the prepared Psf–PPSS–TPA composite cation exchange membrane is well suited for use in V-RFB as a separator.     

Surface Doping of Rutile by Vanadium

A rutile monocrystal was surface-doped with vanadium by sintering with vanadium(V) or vanadium(IV) oxides and investigated by cyclic voltammetry. It is found that vanadium diffuses into the surface layer of rutile forming a mixed oxide. Vanadium atoms in the crystal lattice of rutile are tetravalent, but the vanadium atoms in the first monolayer may be both oxidized to the pentavalent as well as reduced to the trivalent oxidation state. These redox transformations are accompanied by the exchange of oxygen and/or protons between the surface layer of the crystal and the environment as well as the exchange of charge carriers (electrons) with the conduction band edge of rutile.     

Preparation and study of cellulose acetate membranes modified with linear polymers covalently bonded to Starburst polyamidoamine dendrimers

Novel ion‐selective membranes were prepared by means of the noncovalent modification of a cellulose acetate (CA) polymer with either poly(ethylene‐alt‐maleic anhydride) or poly(allylamine hydrochloride) chains covalently linked to Starburst amine‐terminated polyamidoamine (PAMAM) dendrimers generations 4 and 3.5, respectively. Linear polymer incorporation within the porous CA membrane was performed with mechanical forces, which resulted in modified substrates susceptible to covalent adsorption of the relevant dendritic materials via the formation of amide bonds with a carbodiimide activation agent. The membranes thus prepared were characterized by chemical, physical, and spectroscopic measurements, and the results indicate that the dendrimer peripheral functional groups were the species that participated in the ion‐exchange events. The prepared materials were also evaluated for their ion‐exchange permeability with sampled current voltammetry experiments involving cationic and anionic species {[Ru(NH₃)₆]³⁺ and [Fe(CN₆)]^3?, respectively} as redox probe molecules under different pH conditions. As expected, although permeability was favored by opposite charges between the dendrimer and the electroactive probe, a clear blocking effect took place when the charge in the dendritic polymer and the electroactive complex was the same. Electrochemical impedance spectroscopy measurements, on the other hand, showed that the PAMAM‐modified membranes were characterized by good selectivity and low resistance values for multivalent ions compared to a couple of commercial ion‐exchange membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008