• 전기화학회지
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• 제16권3호
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• pp.99-110
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• 2013

레독스 플로우 전지(RFB)는 대형에너지 장치로서 신재생 에너지와 같은 전력발생이 일정하지 못한 상황이나 전력수요가 급증감하여 효율적인 에너지의 운용이 요구될 때 효과적으로 사용할 수 있는 전지모델이다. 일부 상용화된 종류도 있지만 다양한 레독스 쌍과 소재가 연구됨에 따라 개선의 여지가 많은 전지이다. 본 총설에서는 전지의 레독스 쌍(redox pair)의 종류들에 대한 설명을 통하여 레독스 플로우 전지의 전반적인 이해를 돕고자 한다. 레독스 쌍의 혼합오염, crossover, 이온 선택성, 용해도 등의 개선을 통해서 새로운 레독스 플로우 전지의 탄생을 기대할 수 있다. 용량의 개선을 위해서 다양한 수계 및 비수계 레독스 쌍의 연구가 되고 있는데 crossover에 의해 다소의 용량손실이 있다고 하더라도 혼합오염이 없는 전지라면 레독스 플로우 전지의 내구성의 장점을 살릴 수 있을 것이라 기대한다. 혼합오염이 없는 레독스 플로우 전지 중에는 멤브레인이 필요 없는 전지도 새로운 연구방향으로 모색되고 있다.

• Bulletin of the Korean Chemical Society
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• 제32권2호
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• pp.571-575
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• 2011

Graphite-based electrodes were prepared using synthetic graphite (MCMB 1028) or natural graphite (NG) powder using a dimensionally stable anode (DSA) as a substrate. Their electrochemical properties were investigated in vanadiumbased electrolytes to determine how to increase the durability and improve the energy efficiency of redox flow batteries. Cyclic voltammetry (CV) was performed in the voltage range of -0.7 V to 1.6 V vs. SCE at various scan rates to analyze the vanadium redox reaction. The graphite-based electrodes showed a fast redox reaction and good reversibility in a highly concentrated acidic electrolyte. The increased electrochemical activity of the NG-based electrode for the $V^{4+}/V^{5+}$ redox reaction can be attributed to the increased surface concentration of functional groups from the addition of conductive material that served as a catalyst. Therefore, it is expected that this electrode can be used to increase the power density and energy density of redox flow batteries.

• Carbon letters
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• 제28권
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• pp.105-110
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• 2018

Owing to their scalability, flexible operation, and long cycle life, vanadium redox flow batteries (VRFBs) have gained immense attention over the past few years. However, the VRFBs suffer from significant polarization, which decreases their cell efficiency. The activation polarization occurring during vanadium redox reactions greatly affects the overall performance of VRFBs. Therefore, it is imperative to develop electrodes with numerous catalytic sites and a long cycle life. In this study, we synthesized heteroatom-rich carbon-based freestanding papers (H-CFPs) by a facile dispersion and filtration process. The H-CFPs exhibited high specific surface area (${\sim}820m^2g^{-1}$) along with a number of redox-active heteroatoms (such as oxygen and nitrogen) and showed high catalytic activity for vanadium redox reactions. The H-CFP electrodes showed excellent electrochemical performance. They showed low anodic and cathodic peak potential separation (${\Delta}E_p$) values of ~120 mV (positive electrolyte) and ~124 mV (negative electrolyte) in cyclic voltammetry conducted at a scan rate of $5mV\;s^{-1}$. Hence, the H-CFP-based VRFBs showed significantly reduced polarization.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3589-3592
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• 2012

Carbon composite bipolar plates with various carbon black contents were prepared by a compression molding method. The electrical conductivity and electrochemical stability of the bipolar plates have been evaluated. It is found that the electrical conductivity increases with increasing carbon black contents up to 15 wt %. When the carbon black contents are greater than 15 wt %, the electrical conductivity decreases because of a poor compatibility between epoxy resin and carbon black, and a weakening of compaction in the carbon composite bipolar plate. Based on the results, it could be concluded that there are optimum carbon black contents when preparing the carbon composite bipolar plate. Corrosion tests show that the carbon composite bipolar plate with 15 wt % carbon black exhibits better electrochemical stability than a graphite bipolar plate under a highly acidic condition. When the optimized carbon composite bipolar plate is applied to vanadium redox flow cells, the performance of flow cells with the carbon composite bipolar plate is comparable to that of flow cells with the graphite bipolar plate.

• Current Applied Physics
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• 제18권12호
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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.

• Korean Chemical Engineering Research
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• 제53권5호
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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.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1535-1547
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• 2016

This paper proposes various design procedures for computing Power System Ancillary Service Requirement Assessment Indices (PSASRAI) for a Two-Area Thermal Reheat Interconnected Power System (TATRIPS) in a restructured environment. In an interconnected power system, a sudden load perturbation in any area causes the deviation of frequencies of all the areas and also in the tie-line powers. This has to be corrected to ensure the generation and distribution of electric power companies to ensure good quality. A simple Proportional and Integral (PI) controllers have wide usages in controlling the Load Frequency Control (LFC) problems. So the design of the PI controller gains for the restructured power system are obtained using Bacterial Foraging Optimization (BFO) algorithm. From the simulation results, the PSASRAI are calculated based on the settling time and peak over shoot concept of control input deviations of each area for different possible transactions. These Indices are useful for system operator to prepare the power system restoration plans. Moreover, the LFC loop coordinated with Redox Flow Batteries (RFB) has greatly improved the dynamic response and it reduces the control input requirements and to ensure improved PSASRAI, thereby improving the system reliability.

• 한국전기전자재료학회논문지
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• 제31권1호
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• pp.61-67
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• 2018

High-power lithium batteries are suitable for equipment with high power output needs, such as for ESS's initial start-up. However, their management cost is increased by the installation of air-conditioning to minimize the risk of explosion due to internal temperature rise and also by a restriction on the number of charge/discharge cycles. High-capacity flow batteries, on the other hand, have many advantages. They can be used for over 20 years due to their low management costs, resulting from no risk of explosion and a high number of charge/discharge cycles. In this paper, we propose an ESS based on hybrid batteries that uses a lithium iron phosphate battery (LiFePO) at the initial startup and a vanadium redox flow battery (VRFB) from the end of the transient period, with a bi-directional PCS to operate two batteries with different DC voltage levels and using an efficient energy management control algorithm.

• 대한기계학회논문집B
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• 제40권12호
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• pp.777-784
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• 2016

바나듐 전해질 산화-환원 흐름전지(vanadium redox flow batteries, VRFBs)는 간헐적 에너지 저장 시스템의 에너지 저장장치로 사용된다. VRFBs는 재료 및 동작조건에 따라 성능의 차이를 보이며, 각 성능특성에 따른 VRFBs개발이 요구된다. 본 연구에 사용된 단위셀은 반응면적 $25cm^2$이며, 전해액은 0.6의 충전상태를 나타낸다. 방전전류밀도를 0에서 $520mA/cm^2$ 까지 변화시키면서 동시에 전해질 유량도 5mL/min에서 60mL/min까지 변화시켰다. 동일한 입구 전해액 상태에 따른 방전 성능 평가를 위해 4개의 탱크를 사용한 비순환 시스템을 구축하였다. 본 논문은 유량 및 전류밀도의 변화에 대한 단자전압을 측정하였으며, $25cm^2$ 반응면적을 가지는 바나듐계 산화-환원 유동전지 시스템의 최대전류밀도에 대한 실험식을 도출하였다.

• Journal of Electrochemical Science and Technology
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• 제14권2호
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• pp.152-161
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• 2023

Vanadium redox flow batteries (VRFBs) have been considered one of promising power sources for large scale energy storage systems (ESS) because of their excellent cycle performance and good safety. However, VRFBs still have a few challenging issues, such as poor Coulombic efficiency due to vanadium crossover between catholyte and anolyte, although recent efforts have shown promise in electrochemical performance. Herein, the vanadium complexes with various glyme ligands have been examined as active materials to suppress vanadium crossover between catholyte and anolyte, thus improving the Coulombic efficiency of VRFBs. The conventional Nafion membrane has a channel size of ca. 10 Å, whereas vanadium cation species are small compared to the Nafion membrane channel. For this reason, vanadium cations can permeate through the Nafion membrane, resulting in significant vanadium crossover during cycling, although the Nafion membrane is a kind of ion-selective membrane. In this regard, various glyme additives, such as 1,2-dimethoxyethane (monoglyme), diethylene glycol dimethyl ether (diglyme), and tetraethylene glycol dimethyl ether (tetraglyme) have been examined as complexing agents for vanadium cations to increase the size of vanadium-ligand complexes in electrolytes. Since the size of vanadium-glyme complexes is proportional to the chain length of glymes, the vanadium permeability of the Nafion membrane decreases with increasing the chain length of glymes. As a result, the vanadium complexes with tetraglyme shows the excellent electrochemical performance of VRFBs, such as stable capacity retention (90.4% after 100 cycles) and high Coulombic efficiency (98.2% over 100 cycles).