• Current Applied Physics
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• v.18 no.12
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• pp.1507-1512
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• 2018

The development of an organic-based aqueous redox flow battery (RFB) using quinone as an electroactive material has attracted great attention recently. This is because this battery is inexpensive, produces high energy density, and is environment friendly in stationary electrical energy storage applications. Herein, we investigate the redox potentials and solubilities of indole-5,6-quinone and indole-4,7-quinone derivatives in terms of the substituent effects of functional groups using theoretical calculations. Our results indicate that full-site substituted derivatives of indolequinone are more useful as active materials compared to single-site substituted derivatives. In particular, our calculations reveal that the substitution of $-PO_3H_2$ and $-SO_3H$ functional groups with multiple polar bonds is very effective in increasing the activity of the aqueous RFB. As a strategy to overcome the limitation that the aqueous solubility is intrinsically low because they are organic molecules, we suggest the substitution of functional groups with multiple polar bonds to the backbones of active organic materials. Among 180 indolequinone derivatives, 17 candidates that meet the redox potential standards ($${\leq_-}0.2V$$ or $${\geq_-}0.9V$$) and eight candidates with solubility exceeding 2 mol/L are identified. Three indolequinone derivatives that satisfy both conditions are finally presented as promising electroactive candidates for an aqueous RFB.

• Journal of the Korean institute of surface engineering
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• v.54 no.4
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• pp.164-170
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• 2021

Vanadium redox flow batteries (VRFB) have emerged as large-scale energy storage systems (ESS) due to their advantages such as low cross-contamination, long life, and flexible design. However, Hydrogen evolution reaction (HER) in the negative half-cell causes a harmful influence on the performance of the VRFB by consuming current. Moreover, HER hinders V²⁺/V³⁺ redox reaction between electrode and electrolyte by forming a bubble. To address the HER problem, carbon nanotube/graphite felt electrode (CNT/GF) with oxygen functional groups was synthesized through the hydrothermal method in the H₂SO₄ + HNO₃ (3:1) mixed acid solution. These oxygen functional groups on the CNT/GF succeed in suppressing the HER and improving charge transfer for V²⁺/V³⁺ redox reaction. As a result, the oxygen functional group applied electrode exhibited a low overpotential of 0.395 V for V²⁺/V³⁺ redox reaction. Hence, this work could offer a new strategy to design and synthesize effective electrodes for HER suppression and improving the energy density of VRFB.

• Korean Chemical Engineering Research
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• v.53 no.5
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• pp.638-645
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• 2015

Vanadium redox flow batteries (VRFBs) have been investigated for their potential utility as large energy storage systems due to their advantageous performances in terms of long cycle life, high energy efficiency, low cost, and flexible design. Carbon materials are typically used as electrodes in redox reactions and as a liquid electrolyte support. The activities, surface areas, and surface morphologies of porous carbon materials must be optimized to increase the redox flow battery performance. Here, to reduce the resistance in VRFBs, surface-modified carbon felt electrodes were fabricated, and their structural, morphological, and chemical properties were characterized. The surface-modified carbon felt electrode improved the cycling energy efficiencies in the VRFBs, from 65% to 73%, due to the improved wettability with electrolyte. From the results of impedances analysis with proposed fitting model, the electrolyte-coupled polarization in VRFB dramatically decreased upon modification of carbon felt electrode surface. It is also demonstrated that the compressibility of carbon felt electrodes was important to the VRFB polarization, which are concerned with mass transfer polarization. The impedance analysis will be helpful for obtaining better and longer-lived VRFB performances.

• 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.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.2
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• pp.200-205
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• 2017

The three electrodes (carbon felt) were tested in all-vanadium redox flow battery (VRFB) to confirm the its usefulness. The electrode property was measured by the CV (cyclic voltammetry) method. The current ratio of maximum peak(IPA/IPC) in GF040BH5 and GF051BH3 had almost the same value compared to that in XF30A. The performances of VRFB using the each electrode were measured during 5 cycles of charge-discharge at the current density of $60mA/cm^2$. An average energy efficiency of the VRFB was 77.8%, 77.3%, and 79.2% for XF30A, GF040BH5 and GF051BH3, respectively. It was confirmed from the data that GF040BH5 and GF051BH3 is well suited for use in a VRFB as a electrode, like XF30A.

• Membrane Journal
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• v.21 no.2
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• pp.107-117
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• 2011

The all vanadium redox-flow battery (V-RFB) is investigating as one of large-scale power storage systems. Particularly, V-RFB is being investigated as one of the power storage systems for the load leveling and output power equalization of the power systems using renewable energy such as solar and wind. In this paper, it was explained for the principle and construction, recent research review, economy, element technology in V-RFB.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.2
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• pp.106-115
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• 2014

This paper proposes ESS DC-DC Converter using Redox Flow Battery (RFB) for stand-alone microgrid. Price, safety, expandability and dynamics are crucial in ESS. Reports show that Zinc-bromine (ZnBr) RFB is the best choice in ESS. Simple electrical ZnBr RFB model is obtained from charging test. DC-DC converter Inductor current-DClink Voltage model is proposed for the DC microgrid. For the controller design in z-domain, the K-factor method is by considering nature of the digital controller. The control performance has been verified with simulation and hardware experiments. Lastly 10kW DC microgrid using RFB test result is shown.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.4
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• pp.365-371
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• 2016

Cell performance of the Zn-Br redox flow battery (ZBRFB) using two different type's membrane (Nafion117 and SF-600) was evaluated at $20mA/cm^2$ of current density in 1M (mol/L) $ZnBr_2$ + 2M KCl + 0.3M EMPBr(1-ethyl-1-methyl pyrrolidinium bromide) electrolyte. The average energy efficiencies of ZBRFB were 74.9% and 74.7% for Nafion117 and SF-600, respectively. The electrolyte added the 1-ethyl-3-methylimidazolium dicyanamide (EMICA) as an additive was tested for the electrolyte in ZBRFB using SF-600 at $30mA/cm^2$ of current density. An average energy efficiency of the ZBRFB was 74.5% and 77.4% for the electrolyte non-added EMICA and added 1wt% of EMICA, respectively. ZBRFB using the electrolyte added EMICA was showed the higher performance than that using the electrolyte non-added EMICA.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.5
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• pp.531-535
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• 2017

The performance of all-vanadium redox flow battery (VRFB) was tested with an increase of the current density. APS membrane (anion exchange membrane) and GF050CH (cabon felt) were used as a separator and electrode, respectively. An average energy efficiency of the VRFB was 79.5%, 68.1%, and 62.8% for the current density of $60mA/cm^2$, $120mA/cm^2$, and $160mA/cm^2$, respectively. It was confirmed that VRFB can be used as a energy storage system at the higher current density even if the energy efficiency was deceased about 21%.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.17-21
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• 2019

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 an urgent problem. One of the reasons for the low performance is the crossover of the active materials. In this study, the sulfonated Poly (ether ether ketone) (sPEEK) membrane, which is a hydrocarbon membrane, was used instead of the fluorine membrane to reduce the crossover of the active materials. The chromium ion permeability of the sPEEK membrane was $1.8{\times}10^{-6}cm^2/min$, which was about 1/33 of that of the Nafion membrane. Thus, it was shown that the use of the sPEEK membrane instead of the fluorine membrane could solve the high active material crossover problem. The activation energy of iron diffusion through the sPEEK membrane was 24.9 kJ/mol, which was about 66% of Nafion membrane. And that the e-PTFE support in the polymer membrane reduces the active material crossover through Iron-Chrome Redox Flow Battery (ICRFB).