• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.890-894
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• 2018

In this study, methylene blue which is one of dye materials was introduced as active material for aqueous redox flow battery. The redox potential of methylene blue was shifted to negative direction as pH increased. The full-cell performance was evaluated by using methylene blue as the negative active material and vanadium as the positive active material with acid supporting electrolytes. The cell voltage of methylene $blue/V^{4+}$ is very low (0.45 V). In addition, the maximum solubility of methylene blue in water is only 0.12 M. Therefore, the cell test was performed with very low concentration (0.0015 M methylene blue, $0.15M\;V^{4+}$) at first time. Cut-off voltage range was 0 to 0.8 V and $1mA{\cdot}cm^{-2}$ current density was adopted during cycling. As a result, current efficiency (CE) was 99.67%, voltage efficiency (VE), 88.83% and energy efficiency (EE) was 85.87% and discharge capacity was ($0.0500Ah{\cdot}L^{-1}$) at 4 cycle. In addition, the cell test was performed with increased concentration (0.1 M methylene blue, $0.15M\;V^{4+}$) with $10mA{\cdot}cm^{-2}$ current density, leading to higher discharge capacity ($3.8122Ah{\cdot}L^{-1}$) with similar efficiency (CE=99%, VE=85%, EE=85% at 4 cycle).

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.115-116
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• 2013

Recently environmental problems such as greenhouse gas emissions has become a global problem. As a result, the current that can be easily used to Petroleum and coal reserves of fossil energy and environmental issues, coupled with the limitations of this finding for renewable energy to replace the movement is spreading around the world. Among them Energy Storage System with secondary battery technology has been increased interest in, Redox flow batteries, unlike the conventional theory, the life of the rechargeable battery almost no restrictions existing lithium-ion batteries 10 times more than the life of the road. In this paper, power plant or power system, installed in a building that can cope with the rapid increase in demand for power redox flow battery for 100kW PCS will be introduced.

• Membrane Journal
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• v.30 no.1
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• pp.21-29
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• 2020

In this study, we have established the optimum design condition of pore-filled anion-exchange membrane for all-vanadium redox flow battery (VRFB). From the experimental results, it was proven that the membrane design factors that have the greatest influence on the charge-discharge performance of VRFB are the ion exchange capacity, the porosity of substrate film, and the crosslinking degree. That is, the ohmic loss and the crossover of active materials in VRFB were shown to be determined by the above factors. In addition, two methods, i.e. reducing the ion exchange capacity at low crosslinking degree and increasing the crosslinking degree at high ion exchange capacity, were investigated in the preparation of pore-filled anion-exchange membranes. As a result, it was found that optimizing the crosslinking degree at sufficiently high ion exchange capacity is more desirable to achieving high VRFB charge-discharge performances.

• Composites Research
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• v.34 no.3
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• pp.148-154
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• 2021

Carbon/epoxy composite bipolar plate (BP) is a BP that is likely to replace existing graphite bipolar plate of vanadium redox flow cell (VRFB) due to its high mechanical properties and productivity. Multi-functional carbon/epoxy composite BP requires graphite coating or additional surface treatment to reduce interfacial contact resistance (ICR). However, the expanded graphite coating has the disadvantage of having low durability under VRFB operating conditions, and the surface treatments incur additional costs. In this work, an excessive resin absorption method is developed, which uniformly removes the resin rich area on the surface of the BP to expose carbon fibers by applying polyester fabric. This method not only reduces ICR by exposing carbon fibers to BP surfaces, but also forms a unique ditch pattern that can effectively hold carbon felt electrodes in place. The acidic environmental durability, mechanical properties, and gas permeability of the developed carbon/epoxy composite BP are experimentally verified.

• Composites Research
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• v.36 no.6
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• pp.422-428
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• 2023

The electrical contact resistance between the bipolar plate (BP) and the carbon felt electrode (CFE), which are in contact by the stack clamping pressure, has a great impact on the stack efficiency because of the relatively low clamping pressure of the vanadium redox flow battery (VRFB) stack. In this study, a polyethylene (PE) composite-CFE hybrid bipolar plate structure is developed through a local heat welding process to reduce such contact resistance and improve cell performance. The PE matrix of the carbon fiber composite BP is locally melted to create a direct contact structure between the carbon fibers of CFE and the carbon fibers of BP, thereby reducing the electrical contact resistance. Area specific resistance (ASR) and gas permeability are measured to evaluate the performance of the PE composite-CFE hybrid bipolar plate. In addition, an acid aging test is performed to measure stack reliability. Finally, a VFRB unit cell charge/discharge test is performed to compare and analyze the performance of the developed PE composite-CFE hybrid BP and the conventional BP.

• Journal of the Korean Electrochemical Society
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• v.12 no.3
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• pp.263-270
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• 2009

Carbon felt surface was modified by heat or acid treatment in order to use for the electrode of a redox-flow battery. Polymers on the surface of carbon felt was removed and oxygen-containing functional group was attached after the thermal treatment of carbon felt. Thermal treatment was better for the stability of the carbon structure than the acid treatment. Oxygen-containing functional group on the thermally treated carbon felt at 500$^{\circ}C$ was confirmed by XPS and elementary analysis. BET surface area was increased from nearly zero to 96 $m^2/g$. Thermally treated carbon felt at 500$^{\circ}C$ showed lower activation polarization than the thermally treated carbon felt at 400$^{\circ}C$ and the acid-treated carbon felt in the cyclicvoltammetry and polarization experiments. The thermally treated carbon felts at 400$^{\circ}C$ and 500$^{\circ}C$ and the acid-treated carbon felt was applied for the electrode to prepare vanadium redox flow battery. Voltage efficiencies of charge/discharge were 86.6%, 89.6%, and 96.9% for the thermally treated carbon felts at 400$^{\circ}C$ and 500$^{\circ}C$ and the acid-treated carbon felt, respectively.

• Analytical Science and Technology
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• v.28 no.5
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• pp.341-346
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• 2015

In order to understand the counter anionic effects in a non-aqueous vanadium redox flow battery (VRFB), we synthesized four types of electrolyte salts (1-ethyltriethamine tertafluoroborate, [E-TEDA]⁺[BF₄]⁻, 1-ethyltriethamine hexafluorophosphate, [E-TEDA]⁺[PF₆]⁻, 1-butyltriethylamine tertafluoroborate, [B-TEDA]⁺[BF₄]⁻, and 1-buthyltriethamine hexafluorophosphate [B-TEDA]⁺[PF₆]⁻) by counter anion exchange reaction after the SN₂ reaction. We confirmed the successful synthesis of the electrolyte salts [E-TEDA]⁺[Br]⁻ and [B-TEDA]⁺[Br]⁻ via ¹H-NMR spectroscopy and GC-mass analysis before the counter anion exchange reaction. The electric potential of the vanadium acetylacetonate, V(acac)₃, as an energy storage chemical was shown to be 2.2 V in the acetonitrile solvent with each of the [E-TEDA]⁺[BF₄]⁻, [E-TEDA]⁺[PF₆]⁻, [B-TEDA]⁺[BF₄]⁻, and [B-TEDA]⁺[PF₆]⁻ electrolyte salts. In a non-aqueous VRFB with a commercial Neosepta AFN membrane, the maximum voltages reached 1.0 V and 1.5 V under a fixed current value of 0.1 mA in acetonitrile with the [E-TEDA]⁺[BF₄]⁻ and [E-TEDA]⁺[PF₆]⁻ electrolyte salts, respectively. The maximum voltage was 0.8 V and 1.1 V under a fixed current value of 0.1 mA in acetonitrile with the [B-TEDA]⁺[BF₄]⁻ and [B-TEDA]⁺[PF₆]⁻ electrolyte salts, respectively. From these results, we concluded that in the non-aqueous VRFB more of the [PF₆]⁻ counter anion than the [BF₄]⁻ counter anion was transported onto the commercial Neosepta AFN anion exchange membrane.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.674-690
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• 2021

This study proposes a hybrid marine power system combining dual-fuel generators, a fuel cell, and Vanadium Redox Flow Batteries (VRFB). Rigorous verification and validation of the dynamic modelling and integration of the system are conducted. A case study for the application of the hybrid propulsion system to a passenger ship is conducted to examine its time-variant behaviour. A comprehensive model of the reversible and irreversible capacity degradation of the VRFB stack unit is proposed and validated. The capacity retention of the VRFB stack is simulated by being integrated within the hybrid propulsion system. Reversible degradation of the VRFB stack is precisely predicted and rehabilitated based on the predefined operational schedule, while the irreversible portion is retained until the affected components are replaced. Consequently, the advantages of the VRFB system as an on-board ESS are demonstrated through the application of a hybrid propulsion system for liner shipping with fixed routes.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.175.2-175.2
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• 2011

바나듐 3, 4, 5가 이온은 공기 중에서 안정하지만, 바나듐 2가 이온은 쉽게 산화된다. 그러므로 바나듐 2가 이온이 담겨져 있는 음극 탱크가 공기와 접촉하지 않게 하는 것이 중요하다. 충전 중 음극 탱크에 공기가 침투되면, 바나듐 2가 이온은 3가 이온으로 산화되기 때문에 음극과 양극의 전해질에 불균형을 초래한다. 이러한 불균형은 바나듐 레독스 흐름전지 용량저하의 원인이 된다. 본 연구에서는 공기 중 2가 이온 산화에 의한 전해질의 불균형 현상을 쉽게 보여주기 위해, 공기노출과 차단조건에서 충방전 중에 발생한 음극과 양극의 바나듐 이온 상태변화량을 UV-Visible spectrophotometer를 이용해 정량적으로 분석하였다. 분석 결과, 공기노출 조건에서 음극의 충전 시, 충방전 cycle이 진행 될수록 바나듐 2가 이온의 양이 현격히 줄어들었지만, 공기차단 조건에서는 2가 이온의 양이 공기노출 조건보다 훨씬 더 적게 줄어들었다. 즉, 공기차단 조건에서는 바나듐 2가 이온이 3가로 산화되지 않아서 음극의 충전 후 바나듐 3가에서 2가로 전환되는 양이 공기노출 조건보다 더 많은 것을 확인할 수 있었다. 이러한 영향으로 인해, 충방전 10th cycle을 진행해 본 결과, 공기차단 조건에서는 충방전 용량감소가 거의 없었지만 공기노출 조건에서는 현격한 충방전 용량 감소를 보였다.

• Korean Chemical Engineering Research
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• v.56 no.1
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• pp.24-28
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• 2018

The redox flow battery (RFB) is a large-capacity energy storage equipment, and the vanadium redox flow cell is a typical RFB, but VRFB is expensive. Iron-chrome RFBs are economical because they use low-cost active materials, but their low performance is a urgent problem. In this study, the crossover of iron and chromium ion through Nafion membrane and the stability of Nafion membrane in HCl solution were investigated. The permeability of iron and chrome ion through Nafion were $5.5{\times}10^{-5}$ and $6.0{\times}10^{-5}cm^2/min$, respectively, which was 18.9~20.7 times higher than that of vanadium ion ($2.9{\times}10^{-6}cm^2/min$). The crossover of iron and chromium ions were shown to be a cause of performance decrease in Iron-chrome RFB. As the temperature increases, the crossover increases rapidly (activation energy 38.8 kJ/ mol), indicating that operation at low temperature is a methode to reduce the performance loss due to crossover. Nafion membranes were relatively stable in 3 M HCl solution.