Improved properties of positive electrolyte for a vanadium redox flow battery by adding taurine

Taurine was employed as an additive to improve the thermal stability and electrochemical performance of positive electrolyte for a vanadium redox flow battery. The addition of taurine could significantly improve the thermal stability of positive electrolyte, and 2 M V(V) electrolyte with 4 mol% taurine could keep it stable at 40 °C for 120 h, which was 54 h longer than the pristine one. Electrochemical measurements showed that the electrolyte with taurine exhibited superior electrochemical activity and reaction kinetics with a larger diffusion coefficient, exchange current density and reaction rate constant compared with the pristine one. Moreover, the cell using taurine as additive achieved higher average energy efficiency (81.75%) than the pristine cell (79.15%). The Raman and XPS spectroscopy illustrated that taurine could combine with VO²⁺ to form a small molecule complex and the –NH₂ in taurine could be adsorbed on the surface of the electrode to provide more active sites for the electrode reaction, which led to the improvement of mass transfer and the charge transfer process for the V(IV)/V(V) redox reaction.     

A highly concentrated vanadium protic ionic liquid electrolyte for the vanadium redox flow battery

A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery.Despite being less condu...     

Non-aqueous vanadium acetylacetonate electrolyte for redox flow batteries

The electrochemistry of a single-component redox flow battery employing vanadium(III) acetylacetonate in acetonitrile and tetraethylammonium tetrafluoroborate has been investigated. The electrode kinetics of the anodic and cathodic reactions were studied using cyclic voltammetry. The V(II)/V(III) and V(III)/V(IV) couples were quasi-reversible and together yielded a cell potential of 2.2 V. The diffusion coefficient for vanadium acetylacetonate was estimated to be in the range of 1.8–2.9 × 10^?6 cm² s^?1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell, and coulombic efficiencies near 50% were achieved.     

Studies on polypyrrole modified nafion membrane for vanadium redox flow battery

In order to prevent the vanadium crossover and preferential water transfer in all-vanadium redox flow battery (VRFB), three methods – electrolyte soaking, oxidation polymerisation and Electrodeposition, were used to modify Nafion 117 membranes using pyrrole. The surface of the modified membranes was uniform and even, and the membranes were characterised in terms of morphology, membrane area resistance, vanadium permeability and water transfer property. The properties of all the modified membranes were improved greatly. The membranes modified by Electrodeposition showed a best combination of the membrane resistance, vanadium permeability and water transfer property, the experimental results showed that the V(IV) ion permeability of polypyrrole modified Nafion membranes by Electrodeposition at the conditions of 0.025 mA cm⁻² and 0 ^°C for 60 min reduced more than 5 times from 2.87 × 10⁻⁶ cm² min⁻¹ to 5.0 × 10⁻⁷cm² min⁻¹, and the water transfer property decreased more than 3 times from 0.72 ml/72 h cm² to 0.22 ml/72 h cm². All above properties made the modified Nafion membranes more applicative in the VRFB system. This paper also reported other methods for Nafion membrane modification and the influences of the deposition conditions on the properties of the membrane selectivity and water transfer.     

Structure and stability of hexa-aqua V(III) cations in vanadium redox flow battery electrolytes

The vanadium(III) cation structure in mixed acid based electrolyte solution from vanadium redox flow batteries is studied by (17)O and (35/37)Cl nuclear magnetic resonance (NMR) spectroscopy, electronic spectroscopy and density functional theory (DFT) based computational modelling. Both computational and experimental results reveal that the V(III) species can complex with counter anions (sulfate/chlorine) depending on the composition of its solvation sphere. By analyzing the powder precipitate it was found that the formation of sulfate complexed V(III) species is the crucial process in the precipitation reaction. The precipitation occurs through nucleation of neutral species formed through deprotonation and ion-pair formation process. However, the powder precipitate shows a multiphase nature which warrants multiple reaction pathways for precipitation reaction.     

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.     

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.     

Hydrothermal ammoniated treatment of PAN-graphite felt for vanadium redox flow battery

A novel method of hydrothermal ammoniated treatment on the polyacrylonitrile (PAN)-based graphite felt for vanadium redox flow battery was developed. The graphite felt was treated in a Teflon-lined stainless steel autoclave for different time at 180 °C. The content of nitrogen in the PAN graphite felt changed from 3.803% to 5.367% by adjusting treatment time to 15 h in ammonia solution, while FT-IR results indicated that nitrogenous groups were introduced. The electrochemical properties of these graphite felts were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, as well as cell charge and discharge tests. The energy efficiency of the treated graphite felt reached 85% at a current density of 20 mA/cm². The corresponding coulombic efficiency and voltage efficiency were 95.3% and 75.1%, respectively. The improvement of the electrochemical properties for the treated graphite felt might be attributed to the increase of polar nitrogenous groups of carbon fiber surface, which facilitated charge transfer between electrode and vanadium ions.     

Graphene/Nafion ink-impregnated graphite felt for both positive and negative sides of enhanced vanadium redox flow battery

Journal of Solid State Electrochemistry - Electrocatalysts have a key role in the reactions of vanadium redox flow batteries (VRFB). A practical immersion-drying method is used to decorate graphene...     

A review of electrolyte additives and impurities in vanadium redox flow batteries

As one of the most important components of the vanadium redox flow battery(VRFB), the electrolyte can impose a significant impact on cell properties, performance and capital cost. In particular, the electrolyte composition will influence energy density, operating temperature range and the practical applications of the VRFB. Various approaches to increase the energy density and operating temperature range have been proposed. The presence of electrolyte impurities, or the addition of a small amount of other chemical species into the vanadium solution can alter the stability of the electrolyte and influence cell performance, operating temperature range, energy density, electrochemical kinetics and cost effectiveness. This review provides a detailed overview of research on electrolyte additives including stabilizing agents, immobilizing agents, kinetic enhancers, as well as electrolyte impurities and chemical reductants that can be used for different purposes in the VRFBs.     

Highly porous WO3/CNTs-graphite film as a novel and low-cost positive electrode for vanadium redox flow battery

Journal of Solid State Electrochemistry - In this study, novel and low-cost tungsten oxide/carbon nanotubes-graphite-polyvinyl chloride (WO3/CNTs-graphite-PVC) film with porous 3D network structure...     

Water transport study across commercial ion exchange membranes in the vanadium redox flow battery

The water transfer behaviour of Selemion CMV, AMV and DMV membranes (Asahi Glass, Japan) has been studied in the vanadium redox cell, as was the water transfer across Nafion 117 membrane (E.I. Du Pont, USA). The earlier water transport studies of a variety of commercial ion exchange membranes and non-ionic separators in the vanadium redox cell have shown that the net water transport through anion exchange membranes and non-ionic separators in the vanadium redox cell is from the positive half cell (+ve) to the negative half cell (−ve), while for cation exchange membranes the net water transport is in the opposite direction. In the present study, it was found that a significant amount of water is transferred across cation exchange membranes from the −ve vanadium half cell electrolyte to the +ve vanadium half cell electrolyte by the hydration shells of V²⁺ and V³⁺ ions which carry a large amount of water and can easily permeate through cation exchange membranes due to their relatively high charge numbers. The net amount of water of hydration which is transferred across anion exchange membranes from the −ve half cell electrolyte, however, is almost equal to the net amount of water of hydration which is transferred from the +ve half cell electrolyte. Thus, the net amount of water which is transferred across anion exchange membranes is in the same direction as the osmotic water transfer.     

Superior electrocatalytic negative electrode with tailored nitrogen functional group for vanadium redox flow battery

Development of electrodes with high electrocatalytic activity and stability is essential for solving problems that still restrict the extensive application of vanadium redox flow batteries(VRFBs).Here,we designed a novel negative electrode with superior electrocatalytic activity by tailoring nitrogen functional groups,such as newly formed nitro and pyridinic-N transformed to pyridonic-N,from the prenitrogen-doped electrode.It was experimentally confirmed that an electrode with pyridonic-N and ni...     

Electrochemical properties of electrolyte for lead fluoroborate redox flow battery prepared with recovered lead

The electrochemical properties of electrolyte for soluble lead flow battery(SLFB) are a key factor for the improvement of its performance. Pb(BF₄)₂ in which Pb²⁺ ions are highly soluble is cheaper and more stable than conventional Pb(CH₃SO₃)₂. This paper presents the electrochemical properties of HBF₄ and Pb(BF₄)₂ prepared with recovered lead for the electrolytes of SLFB. The density difference of reagent grade and recovered lead electrolytes is less than 0.05 g/cm³ and their viscosities increase up to 132 %, 120 %, respectively when concentration of Pb(BF₄)₂ changes from zero to 2.0 mol·dm⁻³. The conductivity of 1.5 mol·dm⁻³ electrolyte prepared with recovered lead has a peak when concentration of HBF₄ is less than 1.0 mol·dm⁻³. The results of cyclic voltammetry, linear sweep voltammetry and constant current charge/discharge test showed that impurities of recovered lead exert insignificant influences on the Pb²⁺/Pb and Pb²⁺/PbO₂ reactions. These results are promising to apply recovered lead to SLFB.     

Nano oxides incorporated sulfonated poly(ether ether ketone) membranes with improved selectivity and stability for vanadium redox flow battery

Three kinds of sulfonated poly(ether ether ketone) (SPEEK)/nano oxide (Al₂O₃, SiO₂, and TiO₂) composite membranes are fabricated for vanadium redox flow battery (VRFB) application. The composite membranes with 5 wt% of Al₂O₃, SiO₂, and TiO₂ (S/A-5 %, S/S-5 %, and S/T-5 %) exhibit excellent cell performance in VRFB. Incorporation of nano oxides (Al₂O₃, SiO₂, and TiO₂) in SPEEK membrane improves in aspect of thermal, mechanical, and chemical stabilities due to the hydrogen bonds’ interaction between SPEEK matrix and nano oxides. The energy efficiencies (EEs) of composite membranes are higher than that of Nafion 117 membrane, owing to the good balance between proton conductivity and vanadium ion permeability. The discharge–capacity retentions of composite membranes also overwhelm that of Nafion 117 membrane after 200 cycles, indicating their good stability in VRFB system. These low-cost SPEEK/nano oxide composite membranes exhibit great potential for the application in VRFB.     

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.     

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.     

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.     

Novel sulfonated polyimide/ZrO2 composite membrane as a separator of vanadium redox flow battery

Sulfonated polyimide (SPI) and ZrO₂ are blended to prepare a series of novel SPI/ZrO₂ composite membranes for vanadium redox flow battery (VRFB) application. Results of atomic force microscopy and X‐ray diffraction reveal that ZrO₂ is successfully composited with SPI. All SPI/ZrO₂ membranes possess high proton conductivity (2.96–3.72 × 10^?2 S cm^?1) and low VO²⁺ permeability (2.18–4.04 × 10^?7 cm² min^?1). SPI/ZrO₂‐15% membrane is determined as the optimum one on account of its higher proton selectivity and improved chemical stability. The VRFB with SPI/ZrO₂‐15% membrane presents higher coulombic efficiency and energy efficiency than that with Nafion 117 membrane at the current density, which ranged from 20 to 80 mA cm^?2. Cycling tests indicate that the SPI/ZrO₂‐15% membrane has good operation stability in the VRFB system. Copyright © 2014 John Wiley & Sons, Ltd.