Vanadium Redox Flow Battery Single Cell Research Articles

Ultra-thin polytetrafluoroethene/Nafion/silica composite membrane with high performance for vanadium redox flow battery

Ultra-thin and high performance polytetrafluoroethene (PTFE)/Nafion/silica composite membrane has been successfully prepared by solution casting and sol–gel method for all vanadium redox flow battery (VRB). Thickness of ∼25 μm polytetrafluoroethene/Nafion (P/N) membrane is first prepared by impregnating porous PTFE membrane with Nafion solution, and then the P/N membrane is immersed in tetraethoxysilane (TEOS) solution to prepare PTFE/Nafion/silica (P/N/S) composite membranes. The chemical structures of membranes are investigated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), which prove that the Nafion resin and silica are well impregnated in PTFE membrane. The water uptake, proton conductivity, vanadium permeability and VRB single cell tests of the composite membrane are also investigated in detail. At 80 mA cm−2, coulombic efficiency, voltage efficiency and energy efficiency of the VRB with P/N/S-7 (7 wt.% SiO2 in P/N/S) membrane are 93.9%, 87.2% and 81.9%, respectively. Furthermore, the self-discharge rate of the VRB with P/N/S membrane is much slower than that of the VRB with P/N membrane, which indicates that the membrane has good vanadium block ability. Fifty cycles charge–discharge test proves that the P/N/S membrane is very stable and possesses high chemical stability under the strong acid solutions.

A Novel in-Situ Synchrotron XANES Technique to Study All Vanadium Redox Flow Battery

Vanadium redox flow battery (VRB) is one of the most suitable energy storage systems for large-scale intermittently renewable energy storage systems1-2. In the VRB, positive and negative electrolytes play important roles to store the energy3-4. Consequently, in order to develop new electrolyte solutions for the VRBs with higher energy and power density, as well as longer cycling life and better safety characteristics, the in-depth understanding of the relationship between the oxidation state /local structure changes of the electrolytes and electrochemical performance is critically important. Synchrotron radiation based X-ray adsorption fine structure (XAFS) could be very informative when applied to probe the environment around atoms of all states of matter5. Also the X-ray near-edge structure (XANES) could be especially powerful to determine the average oxidation state and local symmetry of the elements in all phases. With these considerations in mind, we carried out in situ XANES measurements during cycling of an all vanadium redox flow battery (VRB). In this study, the home-made VRB single cell was charged at a constant current density up to a 1.65 V, then the cell was discharged at the constant current density until the voltage reach 0.85 V3. In situXANES characterization was performed at the K-edge of the vanadium to monitor the change of the valence state of V in both positive and negative electrolyte solutions. To better illustrate the XANES spectra evolution, 2D contour plots of XANES spectra for both positive and negative electrolytes have been presented in Fig 1(a) and (b). In addition, the VRB voltage profile in the first charge/discharge process is displayed on the side of the XANES spectra. Obviously, the electrochemical process for both sides is well correlated with the evolution of the XANES data. For example, the inflection point at 1.65 V in the voltage profile coincides well the critical point at contour plot of XANES spectra. The spectra of vanadium XANES during the first charge process is shown in Fig 1.(c) and (d). During the first charge process, the electrolytes were charged at a constant current density until the V4+ was converted to V2+ (negative electrode electrolyte) and V5+(positive electrode electrolyte). Hence, in the positive half-cell, the K-edge of the vanadium continuously shifts toward the higher binding energy. This shift indicates an increase in the average valence state of vanadium in the electrolyte (Fig.1c), while the K-edge of vanadium will shifts back to the lower binding energy, which indicate an decrease in the average valence state of vanadium in the electrolyte (not shown in this abstract). Meanwhile, in the negative half-cell, the K-edge of the vanadium continuously shifts toward to the lower binding energy during the charge process (Fig. 1d), while it will shift back during the discharge process (not shown in this abstract). In summary, a new synchrotron based in situ XANES technique has been applied to study the average oxidation state of the electrolytes in the all vanadium redox flow battery (VRB) under realistic cycling conditions. [1] Zhenguo Yang, et al. Chemical reviews., 2011,111, 3577-3613.[2] M. Skyllas-Kazacos, et al. J. Electrochem.Soc., 2011, 158, R55-R79.[3] C. K. Jia, et al. J. Power Sources., 2010,195, 4380-4383.[4] Y Qin, et al. J. Chem. Eng. Data., 2010, 55, 1276-1279.[5] Mansour, et al. Electrochimica Acta., 2002, 47, 3151-3161.

산화그라핀 (Graphene Oxide, GO)이 코팅된 양이온 교환막을 용한 바나듐 레독스 흐름 전지 (Vanadium Redox Flow attery, VRB) 시스템에 관한 연구

바나듐 레독스 흐름 전지 (Vanadium redox flow battery, VRB) 시스템 운전 중 양이온 교환막을 통한 바나듐이온의 투과로 인하여 성능이 저하되는 문제점을 보완하기 위해 판상형태의 탄소물질인 산화그라핀 (Graphene Oxide, GO)을 기존에 사용하였던 양이온 교환막인 Nafion 양이온 교환막 표면에 열압착 방식으로 코팅하여 양이온 교환막 개선 및 VRB 성능 향상을 도모하였다. 개선된 양이온 교환막의 물리화학적 특성분석을 위하여 SEM (Scanning Electron Microscopy)분석, 이온 교환 용량, 수분 흡수 및 수소이온 전도도를 측정하였다. 산화그라핀층을 코팅한 결과, SEM 분석을 통해 양이온 교환막 표면에 약 <TEX>$0.93{\mu}m$</TEX>의 산화그라핀층이 형성된 것을 확인할 수 있었다. 산화그라핀을 코팅하여 개선된 양이온 교환막의 수소이온 전도도 측정 결과, 상용 양이온 교환막의 27% 수준으로 감소하였음을 확인하였으며, 동시에 바나듐이온 투과실험을 실시한 결과, 개선된 양이온 교환막의 바나듐이온 투과도가 기존 상용 양이온 교환막의 25% 이하 수준으로 감소하였음을 확인할 수 있었다. VRB 단위전지 성능실험을 실시하여 충-방전 특성을 분석한 결과, 산화그라핀을 코팅하여 개선된 양이온 교환막을 VRB 시스템에 적용하였을 경우, 바나듐이온의 투과도 감소로 인하여 쿨롱효율이 증가하였음을 확인할 수 있었고, 그로 인하여 전체적인 에너지효율이 상용막을 적용하였을 때 보다 증가하였음을 확인할 수 있었다. 따라서, 본 연구를 통해 양이온 교환막 표면에 판상형태의 탄소물질인 산화그라핀을 코팅하는 방법이 바나듐이온 투과도를 저하시키고 VRB의 시스템성능을 향상시킬 수 있는 효과적인 방법임을 제시할 수 있었다. Cation exchange membrane (Nafion) was modified to reduce the vanadium ion permeation through the membrane and to increase the vanadium redox flow battery (VRB) system performance by coating the graphene oxide (GO) which has nano-plate like morphology. Modified membrane properties were studied by measuring the ion exchange capacity (I.E.C), water uptake and proton conductivity. The thickness of the coated layer on the surface of the Nafion membrane was observed as <TEX>$0.93{\mu}m$</TEX> by SEM. Proton conductivity and vanadium ion permeability of the modified membrane were decreased to 27% and 25% compared to that of the commercial Nafion membrane respectively. VRB single cell performance test was performed to compare the system performance of the VRB applied with commercial Nafion membrane and modified membrane. VRB system applied with modified membrane showed higher coulombic efficiency and energy efficiency than the VRB system applied with the commercial Nafion membrane due to the reduction of the vanadium ion permeation. From these result, we could suggest that the membrane modification by coating the GO on the surface of the Nafion membrane could be one of the promising strategies to reduce the vanadium ion permeation and to increase the VRB system performance effectively.

Preparation of the graphene oxide (GO)/Nafion composite membrane for the vanadium redox flow battery (VRB) system

Graphene oxide (GO) nano-plate was applied to the vanadium redox flow battery (VRB) system as the ion-exchange membrane to reduce the vanadium permeation and enhance the VRB system performance. The GO/Nafion membranes were prepared with the GO composition from 0.001 wt% to 1 wt%. The prepared composite membranes were analyzed by SEM to investigate the microstructure of the membranes. Water uptake, proton conductivity, thickness and vanadium ion permeability of the membrane were observed to evaluate the membrane properties. X-ray diffraction (XRD) analysis was conducted to observe the inter-planar microstructure of the membranes. The prepared membranes had a lower value of the inter-planar space dimension than that of the Nafion 117 membrane and because of this fact the prepared composite membrane had a lower value of the water uptake, vanadium permeability and proton conductivity than that of the Nafion 117. The value of the proton conductivity and the vanadium permeability were decreased when increasing the GO composition in the composite membrane. The optimum composition of the GO in the composite membranes for the application of the ion-exchange membrane of the VRB system ranged from 0.01 wt% to 0.1 wt%. The highest EE value of the VRB single cell was obtained by using the 0.01 wt% GO composite membrane and the value was 82.5%. We could suggest that the GO/Nafion composite membrane can be one of the promising candidates for the VRB membrane electrolyte.

Novel sulfonated poly (ether ether keton)/polyetherimide acid-base blend membranes for vanadium redox flow battery applications

Novel acid-base blend membranes composed of sulfonated poly (ether ether ketone) (SPEEK) and polyetherimide (PEI) were prepared for vanadium redox flow battery (VRB). The blend membranes were characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electronic microscopy (SEM). The ion exchange capacity (IEC), proton conductivity, water uptake, vanadium ion permeability and mechanical properties were measured. As a result, the acid-base blend membranes exhibit higher water uptake, IEC and lower vanadium ion permeability compared to Nafion117 membranes and all these properties decrease with the increase of PEI. In VRB single cell test, the VRB with blend membranes shows lower charge capacity loss, higher coulombic efficiency (CE) and energy efficiency (EE) than Nafion117 membrane. Furthermore, the acid-base blend membranes present stable performance up to 50 cycles with no significant decline in CE and EE. All experimental results indicate that the SPEEK/PEI (S/P) acid-base blend membranes show promising prospects for VRB.

Sulfonated poly(ether ether ketone)/mesoporous silica hybrid membrane for high performance vanadium redox flow battery

Hybrid membranes of sulfonated poly(ether ether ketone) (SPEEK) and mesoporous silica SBA-15 are prepared with various mass ratios for vanadium redox flow battery (VRB) application and investigated in detail. The hybrid membranes are dense and homogeneous with no visible hole as the SEM and EDX images shown. With the increasing of SBA-15 mass ratio, the physicochemical property, VO2+ permeability, mechanical property and thermal stability of hybrid membranes exhibit good trends, which can be attributed to the interaction between SPEEK and SBA-15. The hybrid membrane with 20 wt.% SBA-15 (termed as S/SBA-15 20) shows the VRB single cell performance of CE 96.3% and EE 88.1% at 60 mA cm−2 due to its good balance of proton conductivity and VO2+ permeability, while Nafion 117 membrane shows the cell performance of CE 92.2% and EE 81.0%. Besides, the S/SBA-15 20 membrane shows stable cell performance of highly stable efficiency and slower discharge capacity decline during 120 cycles at 60 mA cm−2. Therefore, the SPEEK/SBA-15 hybrid membranes with optimized mass ratio and excellent VRB performance can be achieved, exhibiting good potential usage in VRB systems.

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.

Poly(vinylbenzyl chloride-glycidyl methacrylate)/Polyethylene Composite Anion Exchange Membranes for Vanadium Redox Battery Application

Anion exchange membranes for a vanadium redox flow battery (VRB) were prepared by pore-filling on a PE substrate with the copolymerization of vinylbenzyl chloride (VBC) and glycidyl methacrylate (GMA). The ion exchange capacity, water uptake and weight gain ratio were increased with a similar tendency up to 65% of GMA content, indicating that the monomer improved the pore-filling degree and membrane properties. The vanadium ion permeability and open-circuit voltage were also investigated. The permeability of the VG65 membrane was only 1.23 × 10 cm min compared to 17.9 × 10 cm min for Nafion 117 and 1.8 × 10 cm min for AMV. Consequently, a VRB single cell using the prepared membrane showed higher energy efficiency (over 80%) of up to 100 cycles compared to the commercial membranes, Nafion 117 (ca. 58%) and AMV (ca. 70%).

Electrochemical activation of graphite felt electrode for VO2+/VO2+ redox couple application

In this work, the electrochemical activation of graphite felt electrode for vanadium redox flow battery (VRB) was studied. Graphite felt (GF) electrode was oxidized at a range of electrochemical oxidation degrees in H2SO4 solution. The electrochemical performance of the treaded GF was discussed, and the law of the surface properties of GF which changed along with the electrochemical oxidation degree was proposed. The structure, composition, surface tension and electrochemical properties of the oxidized GF (OGF) were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The GF oxidized at 560–840mAhg−1 exhibited the best activity toward VO2+/VO2+ redox reaction, according with the highest COH and COOH content (ca. 34%) on its surface. The mechanisms of VO2+/VO2+ redox reaction on OGF were also discussed. VRB single cell with pristine GF and OGF as the electrode were test at various charge–discharge current densities, respectively. The columbic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) of the cell using OGF electrode are much higher than the cell using pristine GF, suggested that the electro-oxidation method is a promising technology for the activation of GF electrode.

Carbon felt supported carbon nanotubes catalysts composite electrode for vanadium redox flow battery application

A modified electrode for vanadium redox flow battery (VRFB) has been developed in this paper. The electrode is based on a traditional carbon felt (CF) grafted with the short-carboxylic multi-walled carbon nanotubes (MWCNTs). The microstructure and electrochemical property of the modified electrode as well as the performance of the VRFB single cell with it have been characterized. The results show that the MWCNTs are evenly dispersed and adhere to the surface of carbon fibres in the CF. The electrochemical activities of the modified CF electrode have been improved dramatically and the reversibility of the VO2+/VO2+ and V3+/V2+ redox couples increased greatly. The VRFB single cell with the modified CF exhibits higher coulombic efficiency (93.9%) and energy efficiency (82.0%) than that with the pristine CF. The SEM analysis shows that the MWCNTs still cohere with carbon fibres after charge and discharge test, indicating the stability of the MWCNTs in flowing electrolyte. Therefore, the composite electrode presents considerable potential for the commercial application of CF in VRFB.

Sulfonated polyimide/chitosan composite membrane for vanadium redox flow battery: Membrane preparation, characterization, and single cell performance

AbstractA novel sulfonated polyimide/chitosan (SPI/CS) composite membrane was prepared from self‐made SPI (50% of sulfonation degree) through an immersion and self‐assembly method, which was successfully applied in vanadium redox flow battery (VRB). The proton conductivity of SPI/CS composite membrane is effectively improved compared to the plain SPI membrane. The VO2+ permeability coefficient across SPI/CS composite membrane is 1.12 × 10−7 cm2 min−1, which is only one tenth of that of Nafion® 117 membrane. Meanwhile, the proton selectivity of SPI/CS composite membrane is about eight times higher than that of Nafion® 117 membrane. In addition, the oxidative stability SPI/CS composite membrane is superior to that of pristine SPI membrane. The VRB single cell using SPI/CS composite membrane showed higher energy efficiency (88.6%) than that using Nafion® 117 membrane, indicating that SPI/CS composite membrane is a promising proton conductive membrane for VRB application. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation and characterization of sulfonated poly(ether sulfone)/sulfonated poly(ether ether ketone) blend membrane for vanadium redox flow battery

A blend membrane consisting of sulfonated poly(ether sulfone) (SPES) and sulfonated poly(ether ether ketone) (SPEEK) (we name it as SPES/SPEEK membrane) for vanadium redox flow battery (VRB) has been fabricated and characterized. The swelling behavior and water uptake of SPES/SPEEK membrane are evaluated in terms of the morphology phase characterization by atom force microscopy (AFM). The results indicate that SPES/SPEEK membrane possesses significantly strong mechanical strength, high water uptake and low permeability of VO2+ ions. The performance of VRB single cell with SPES/SPEEK membrane shows significantly lower charge capacity loss, higher coulombic efficiency (CE) and energy efficiency (EE) (98% vs. 91% and 84% vs. 79.5%, respectively) compared to that with Nafion 212 membrane. Furthermore, the SPES/SPEEK membrane presents good cell performance up to 100 cycles (more than 265 h) with no significant decline in CE and EE. With all the good properties and low cost, the SPES/SPEEK membrane shows promising prospects for application in VRB.

Sulfonated polyimide/chitosan composite membrane for vanadium redox flow battery: Influence of the infiltration time with chitosan solution

In order to probe the effect of the infiltration time with chitosan solution, a series of sulfonated polyimide/chitosan (SPI/CS) composite membranes with different infiltration time including 6h, 12h, 24h and 36h were prepared and applied in vanadium redox flow battery (VRB) system. SEM images demonstrate the presence of thin CS layer on the surface of SPI membrane, and the thickness of the CS layer increases with the infiltration time. The proton conductivity and the vanadium ion barrier property of SPI/CS composite membranes increase with the increment of the infiltration time. The SPI/CS-24 and SPI/CS-36 membranes show similar proton selectivity which is over eight times of that of Nafion® 117 membrane. VRB single cell using SPI/CS membrane reveals higher coulombic efficiency (CE) and energy efficiency (EE) than that using Nafion® 117 membrane. In particular, the CE and EE for SPI/CS-24 membrane achieve 97.8% and 88.6% respectively. All experimental results indicate that the SPI/CS composite membranes are promising proton conducting membranes for VRB, among which SPI/CS-24 membrane exhibits the best combination property.

Nafion-sulfonated organosilica composite membrane for all vanadium redox flow battery

A novel Nafion-sulfonated diphenyldimethoxysilane (N-sDDS) composite membrane is prepared and employed in vanadium redox flow battery (VRB). Ion exchange capacity, proton conductivity, water transport behavior, and the cell performances are characterized. Fourier transform-infrared and X-ray diffraction analysis indicate that the sulfonated diphenyldimethoxysilane (sDDS) particles are successfully introduced into the Nafion matrix. In VRB single cell test, the VRB with N-sDDS membrane exhibits nearly the same coulombic efficiency as the unmodified Nafion membrane, but higher voltage efficiency than that of the VRB with unmodified Nafion membrane. The VRB with N-sDDS composite membrane keeps a stable performance after 60 times charge–discharge test. In the self-discharge test, the VRB with the N-sDDS membrane presented a lower self-discharge rate than that of the VRB with Nafion membrane. All results show that the addition of s-DDS is a simple and efficient way to improve the conductivity of Nafion, and the composite membrane shows good potential use for VRB.

Poly(tetrafluoroethylene) reinforced sulfonated poly(ether ether ketone) membranes for vanadium redox flow battery application

Poly(tetrafluoroethylene) reinforced sulfonated poly(ether ether ketone) (SPEEK/PTFE) composite membranes are prepared for vanadium redox flow battery (VRB) application. Results show that SPEEK/PTFE composite membranes have lower water uptake and swelling ratio than that of SPEEK membranes due to the PTFE reinforcement. As a result, the composite membranes show higher elongation ratio and better mechanical stability than SPEEK membranes. VRB single cell tests are also carried out to further evaluate their performance. The batteries assembled with SPEEK/PTFE membranes exhibit higher columbic efficiency (CE) and energy efficiency (EE) than that of SPEEK membranes. Furthermore, the composite membranes show much better stability than pristine SPEEK, confirming that PTFE can effectively reinforce membranes to improve their chemical and mechanical stability under VRB operating condition.

SPPEK/WO3 hybrid membrane fabricated via hydrothermal method for vanadium redox flow battery

A SPPEK/WO3 hybrid membrane was fabricated by a hydrothermal method to improve its performance in vanadium redox flow battery (VRB). The morphology of the hybrid membrane revealed that WO3 phase was well formed in the SPPEK matrix. At 50mA/cm2, the VRB single cell with SPPEK/WO3 membrane presented a lower self-discharge rate (218h above 0.8V) and a higher coulombic and energy efficiency (98.07% and 78.06%), ascribed to its higher ionic selectivity (5.81×104minS/cm3), compared with Nafion system. The hybrid membrane exhibited a stable performance during 100cycles.

A multilayered membrane for vanadium redox flow battery

In order to reduce the vanadium ions permeability of membranes used in vanadium redox flow battery (VRB) while keeping its chemical stability, sulfonated poly(ether ether ketone) (SPEEK)/polypropylene (PP)/perfluorosulfonic acid (PFSA) layered composite membrane (we name it as S/P/P membrane) has been fabricated and characterized. In the S/P/P membrane, polypropylene plays a role of central layer, which is sandwiched by SPEEK and PFSA layer. Results show that S/P/P membrane presents a very low permeability of vanadium ions, accompanied by slightly higher area resistance than that of Nafion 212 membrane (N212). The VRB single cell with S/P/P membrane shows higher coulombic efficiency but lower voltage efficiency in comparison with the one with N212. The performance of VRB with S/P/P membrane can be maintained after more than 50 cycles. Our experimental results suggest that the S/P/P membrane approach is a promising strategy to suppress the migration of vanadium ions in VRB, while retaining an outstanding VRB performance.

Nafion/polyvinylidene fluoride blend membranes with improved ion selectivity for vanadium redox flow battery application

Nafion/PVDF blends are employed to prepare the ion exchange membranes for vanadium redox flow battery (VRB) application for the first time. The addition of the highly crystalline and hydrophobic PVDF effectively confines the swelling behavior of Nafion. In VRB single cell test, the Nafion/PVDF binary membranes exhibit higher columbic efficiency than recast Nafion at various current densities. The blend membrane with 20 wt% of PVDF (N 0.8P 0.2) shows energy efficiency of 85% at 80 mA cm −2, which is superior to that of recast Nafion. N 0.8P 0.2 membrane also possesses twice longer duration in OCV decay test and much lower permeation of VO 2+ compared with recast Nafion. These results indicate that the addition of PVDF is a simple and efficient way to improve the ion selectivity of Nafion, and the polymer blends with optimized mass fraction of PVDF show good potential for VRB application.

Preparation of chloromethylated/quaternized poly(phthalazinone ether ketone) anion exchange membrane materials for vanadium redox flow battery applications

Chloromethylated poly(phthalazinone ether ketone) (CMPPEK) was prepared from poly(phthalazinone ether ketone), with chloromethyl methyl ether (CME) as the chlromethylating reagent and concentrated sulfuric acid as the solvent. The effects of CME quantity, reaction temperature, and reaction time on degree of chloromethylation (DCM) were investigated. CMPPEK with DCM ranging from 0.73 to 2.32 mmol g −1 were obtained. CMPPEK were characterized with 1H NMR and TGA. CMPPEK membranes were prepared from CMPPEK/ N-methyl-2-pyrrolidinone casting solutions. Quaternized poly(phthalazinone ether ketone) (QAPPEK) anion exchange membranes were prepared from CMPPEK membranes with different DCM. The ion exchange capacity (IEC) and water content (Wc) of QAPPEK membranes were studied. QAPPEK membranes exhibited IEC ranging from 0.70 to 2.04 mmol g −1 and Wc ranging from 12.9 to 52.3%. IEC and Wc of QAPPEK increased with an increase in DCM of CMPPEK. The vanadium ion permeability of QAPPEK membranes was much lower than that of Nafion117 membrane. The performance of vanadium redox flow battery (VRB) single cell with QAPPEK membranes was investigated. Compare to VRB cell with Nafion117 membrane, the VRB single cell with QAPPEK membranes exhibited higher columbic efficiency. The results show that QAPPEK membranes could be promising anion exchange membranes for VRB applications.

Preparation and properties of sulfonated poly(fluorenyl ether ketone) membrane for vanadium redox flow battery application

In order to develop novel membranes for vanadium redox flow battery (VRB) with low self-discharge rate and low cost, sulfonated poly(fluorenyl ether ketone) (SPFEK) was synthesized directly via aromatic nucleophilic polycondensation of bisphenol fluorene with 60% sulfonated difluorobenzophenone and 40% difluorobenzophenone. The SPFEK membrane shows the lower permeability of vanadium ions. The open circuit voltage evaluation demonstrates that the SPFEK membrane is superior to Nafion 117 membrane in self-discharge test. Both energy efficiencies (EE) and power densities of the VRB single cell based on the SPFEK membrane are higher than those of the VRB with Nafion 117 membrane at the same current densities. The highest coulombic efficiency (CE) of VRB with SPFEK membrane is 80.3% while the highest CE of the VRB with Nafion 117 membrane is 77.0%. The SPFEK membrane shows the comparative stability to Nafion 117 membrane in VO 2 + electrolyte. The experimental results suggest that SPFEK membrane is a promising ion exchange membrane for VRB.