Redox Flow Battery용 일체화된 흑연/DSA 전극의 전기화학적 특성

김형선,Kim, Hyung-Sun 한국전기화학회 2010 한국전기화학회지 Vol.13 No.2

Redox Flow Battery용 고내구성 및 고효율 전극의 제조를 위해 DSA(Dimensionally Stable Anode)를 집전체 및 전극으로 사용하고 흑연 입자를 이용한 전극을 제조하여 DSA와 압연하는 방법으로 일체화 된 흑연/DSA 전극의 전기화학적 특성을 조사하였다. 1 M $VOSO_4$ + 5M $H_2SO_4$ 혼합용액과 2 M $VOSO_4$ + 2.5M $H_2SO_4$ 혼합된 용액의 전해액 시스템에서 Cyclic Voltammetry(CV) 방법을 이용하여 -0.7 V에서 1.6 V vs. SCE의 전위범위에서 전극의 특성을 실험한 결과, 높은 농도의 2M $VOSO_4$ 전해액에서도 바나듐 이온들의 redox couple 반응을 잘 나타내고 있으며 가역성도 우수한 것으로 나타났다. 따라서 본 연구에서 제조된 일체화된 흑연/DSA 전극을 redox flow battery에 적용할 경우에 고내구성, 내부식성 및 전지의 에너지밀도, 출력밀도와 에너지효율을 향상시킬 것으로 판단된다. An assembled-graphite/DSA(Dimensionally Stable Anode) was prepared using graphite powder to increase durability and energy efficiency of redox flow battery and investigated its electrochemical properties in vanadium-based electrolyte. The cyclic voltammetry (CV) was carried out in the voltage range of -0.7V and 1.6V vs. SCE at 5 mV/sec scan rate to analyze vanadium redox reaction. From the CV results, the assembled-graphite/DSA electrode showed a fast couple reaction and good reversibility in 2M $VOSO_4$ + 2.5 M $H_2SO_4$ electrolyte. Therefore, it has been expected that this electrode increases power density as well as energy density of redox flow battery.

A high-temperature tolerance solution for positive electrolyte of vanadium redox flow batteries

Kim, D.,Jeon, J. Elsevier Sequoia 2017 Journal of electroanalytical chemistry Vol.801 No.-

Vanadium redox flow battery (VRFB) is attractive for energy storage applications, but there still remains a problem of preventing V-precipitation reaction (i.e., V<SUB>2</SUB>O<SUB>5</SUB>) to provide the thermal stability of electrolyte employed in VRFB. The V<SUB>2</SUB>O<SUB>5</SUB> precipitation is accelerated in the positive electrolyte under high temperature, resulting in decreasing the charge capacity and energy efficiency of VRFB. So far, previous supporting materials, which are used to solve such precipitation problem, provide a disadvantage of decreasing voltage efficiency of VRFBs by increasing electrolyte resistance. This paper describes an advanced vanadium-positive electrolyte with high-temperature tolerance for high-efficiency VRFBs, which uses a sodium formate as a supporting material. The sodium formate plays a role as an agent capable of preventing precipitation reaction in the positive electrolyte and it also provides an effect of decreasing a viscosity of the positive electrolyte. The effectiveness of the proposed electrolyte solution is demonstrated through the following experiments: UV-vis spectrometry, viscosity measurement, cyclic voltammetry (CV), VRFB operation and scanning electron microscopy (SEM) analysis. Then, for the performance comparison of high temperature stability, all experiments are carried out at 60<SUP>o</SUP>C. Experimental results show that using the sodium formate leads to near 4.5 times increase of diffusion coefficient as compared to conventional electrolyte, and also provides 20.2% higher charge capacity (50th cycle) and 2.27% higher average energy efficiency (50cycles) at the current density of 80mAcm<SUP>-2</SUP>. In addition, it appears that the precipitation of vanadium species is not observed in the electrolyte during VRFB operation. Therefore, this paper provides that new direction about effect of the additive in the positive electrolyte and the sodium formate can be considered as a promising additive for high-performance electrolyte of VRFBs.

Urea를 이용한 바나듐 레독스 흐름 전지용 카본 펠트 전극 개발

김소연,김한성 한국화학공학회 2019 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.57 No.3

In this study, nitrogen doped carbon felt was prepared by pyrolysis of urea at high temperature and applied as an electrode for vanadium redox flow cell. Urea is easier to handle than ammonia and forms NH2 radicals at higher temperatures, creating a nitrogen functional group on the carbon surface and acting as an active site in the vanadium redox reaction. Therefore, the discharge capacity of activated carbon felt electrodes using urea was 14.9 Ah/L at a current density of 150 mA/cm2, which is 23% and 187% higher than OGF and GF, respectively. These results show the possibility that activated carbon felt electrode using urea can be used as electrode material for redox flow battery. 본 연구에서는 urea를 이용해 질소 도핑된 카본 펠트 전극을 제조하고 이를 바나듐 레독스 흐름 전지용 전극으로 적용하였다. Urea는 암모니아 보다 취급이 용이할 뿐 아니라 고온 열분해를 통해 NH2 라디칼이 발생하여 탄소 표면에질소 작용기를 만들고 이는 바나듐 이온의 산화/환원 반응을 향상시키는 활성점(active site)로 작용한다. Urea로 활성화된 카본 펠트 전극은 150 mA cm2의 전류 밀도에서 14.9 Ah/L의 방전 용량을 보였으며 이는 산소작용기로 활성화된 카본 펠트(OGF) 및 비활성화 카본 펠트(GF)보다 각각 23% 및 187% 더 높았다. 이러한 결과는 urea로 활성화된카본 펠트 전극이 레독스 흐름 전지용 전극 소재로 사용될 수 있는 가능성을 보여준다.

Multimodal porous and nitrogen-functionalized electrode based on graphite felt modified with carbonized porous polymer skin layer for all-vanadium redox flow battery

Yang, Dae-Soo,Han, Jae Hee,Jeon, Jun Woo,Lee, Jang Yong,Kim, Dong-Gyun,Seo, Dong Hack,Kim, Byoung Gak,Kim, Tae-Ho,Hong, Young Taik Elsevier 2019 Materials today energy Vol.11 No.-

<P><B>Abstract</B></P> <P>Novel nitrogen-functionalized multimodal porous graphite felt (GF) electrodes for all-vanadium redox flow batteries (VRFB) have been developed using a simple binder-free fabrication method. We synergistically combined a polymer of intrinsic microporosity (PIM), as a carbon and nitrogen precursor, with vapor-induced phase separation. The GF with a carbonized PIM skin layer showed a high surface area and multimodal pore architecture featuring interconnected micro-, meso-, and macropores. The enhanced electrochemical reactivity and wettability, and excellent electronic conductivity of the prepared electrodes successfully improved the overall kinetics of the redox reactions of the vanadium ion species by providing highly active catalytic sites and efficient ion and electron transport pathways. This resulted in the outstanding performance of VRFB single cells using this material as electrodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new strategy for creating porous electrocatalytic skin layer on the carbon felt. </LI> <LI> Multimodal N-doped carbon electrode with interconnected micro-, meso-, and macropores. </LI> <LI> Large surface area, excellent wettability, and outstanding electrocatalytic activity. </LI> <LI> High energy efficiency and rate capability in vanadium redox flow battery. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Nanostructured Electrocatalysts for All-Vanadium Redox Flow Batteries.

Park, Minjoon,Ryu, Jaechan,Cho, Jaephil Wiley-VCH 2015 Chemistry - An Asian Journal Vol.10 No.10

<P>Vanadium redox reactions have been considered as a key factor affecting the energy efficiency of the all-vanadium redox flow batteries (VRFBs). This redox reaction determines the reaction kinetics of whole cells. However, poor kinetic reversibility and catalytic activity towards the V(2+) /V(3+) and VO(2+) /VO2 (+) redox couples on the commonly used carbon substrate limit broader applications of VRFBs. Consequently, modified carbon substrates have been extensively investigated to improve vanadium redox reactions. In this Focus Review, recent progress on metal- and carbon-based nanomaterials as an electrocatalyst for VRFBs is discussed in detail, without the intention to provide a comprehensive review on the whole components of the system. Instead, the focus is mainly placed on the redox chemistry of vanadium ions at a surface of various metals, different dimensional carbons, nitrogen-doped carbon nanostructures, and metal-carbon composites.</P>

탄소펠트의 산화처리 방법이 바나듐 레독스 흐름 전지의 전극 성능에 미치는 영향

하달용,김상경,정두환,임성엽,백동현,이병록,이관영,Ha, Dal-Yong,Kim, Sang-Kyung,Jung, Doo-Hwan,Lim, Seong-Yop,Peck, Dong-Hyun,Lee, Byung-Rok,Lee, Kwan-Young 한국전기화학회 2009 한국전기화학회지 Vol.12 No.3

레독스 흐름 전지의 전극으로 사용하기 위해 탄소펠트를 열처리와 산처리 방법으로 산화 개질하였다. 열중량 분석결과 열처리 또는 산처리에 의하여 탄소펠트의 섬유 표면에 고분자 물질이 제거되고 산소 관능기가 도입된 것을 확인할 수 있었으며 습식 방법인 산처리 방법보다 건식방법인 열처리 방법이 기계적 안정성을 유지하는데 효과적인 처리 방법으로 나타났다. XPS, 원소분석을 통하여 500$^{\circ}C$에서 4시간 열처리한 탄소펠트의 표면에 산소 관능기가 부가된 것을 확인하였으며 질소흡착실험에서 거의 없던 표면적이 96 $m^2/g$로 증가한 것을 알 수 있었다. CV실험 및 분극 실험을 수행한 결과 500$^{\circ}C$ 열처리 전극의 활성화 저항이 가장 낮게 나타났다. 산처리한 탄소펠트와 400$^{\circ}C$, 500$^{\circ}C$에서 열처리한 탄소펠트를 이용하여 바나듐 레독스 흐름 전지를 구성하고 충/방전 실험을 실시한 결과 충/방전 전압효율이 산처리 전극의 경우 86.6%, 400$^{\circ}C$ 열처리 전극의 경우 89.6%, 500$^{\circ}C$ 열처리 전극의 경우 90.6%로 500$^{\circ}C$ 열처리 전극이 가장 우수하였다. 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.

Vanadium Redox Flow Battery Using Electrocatalyst Decorated with Nitrogen-Doped Carbon Nanotubes Derived from Metal-Organic Frameworks

Noh, Chanho,Lee, Chang Soo,Chi, Won Seok,Chung, Yongjin,Kim, Jong Hak,Kwon, Yongchai The Electrochemical Society 2018 Journal of the Electrochemical Society Vol.165 No.7

<P>Highly porous zeolitic-imidazole frameworks (ZIFs) are synthesized to produce N-doped mesoporous carbon electrocatalysts via calcination. The N-doped carbon (m-NC) and carbon nanotubes (m-NCNT) are obtained from ZIF-8 and ZIF-67, while the core-shell structure of ZIF-8@ZIF-67 produced with ZIF-8 seeds (m-NC@NCNT) is prepared by hydrothermal method. Chemical and optical evaluations of the catalysts are characterized using BET, FT-IR, XPS, XRD, Raman spectroscopy and SEM/STEM and they are used as the catalysts for redox reactions of vanadium ions and redox flow battery (VRFB) performance. In the utilization, m-NC@NCNT and m-NCNT are effective for improving VO2+/VO2+ redox reaction, although m-NC does not influence that. Even in VRFB tests using the catalysts, charge/discharge potential and energy efficiency (EE) of m-NC@NCNT and m-NCNT are highest, not to mention excellent EE resilience after undergoing tougher cycling condition. These results are due to the large graphitic-N portion of the two catalysts. Namely, electrons produced by the graphitic-N are delocalized, forming pi-conjugated system and vanadium-nitrogen transition state. This state then promotes electron transfer during VO2+/VO2+ redox reaction and VRFB performance. (C) 2018 The Electrochemical Society.</P>

Redox flow battery용 carbon felt 전극의 전기화학적 산화

정영관,황갑진,김재철,유철휘 한국수소및신에너지학회 2011 한국수소 및 신에너지학회논문집 Vol.22 No.5

All vanadium redox-flow battery (VRFB) has been studied actively as one of the most promising electrochemical energy storage systems for a wide rage of applications such as electric vehicles, photovoltaic arrays, and excess power generated by electric power plants at night time. In this study, carbon felt electrodes were treated by electrochemical oxidation with KOH, and the cyclic voltammetry were studied in order to investigate redox reactivity of vanadium ion species with carbon felt electrodes. Besides the effect of electrochemical oxidation on the surface chemistry of carbon felt electrodes were investigated using the X-ray photoelectron spectroscopy (XPS). After electrochemical oxidation, XPS analysis of PAN based GF20-3carbon felt electrode revealed on increase in the overall surface oxygen content of the carbon felts after electrochemical oxidation. Redox reaction characteristics using cyclic voltammetry (CV) were ascertained that the electrochemical treated electrode were more reversible than the untreated electrode.

오존, 암모니아 순차적 처리를 통한 바나듐 레독스 흐름 전지용 활성화 카본 펠트 전극 개발

최한솔,김한성 한국수소및신에너지학회 2021 한국수소 및 신에너지학회논문집 Vol.32 No.4

A carbon felt electrode was prepared using ozone and ammonia sequential treatment and applied as an electrode for a vanadium redox flow battery (VRFB). The physical and electrochemical analyses demonstrate that the oxygen groups facilitate nitrogen doping in the carbon felt. Carbon felt (J5O3+NH3), which was subjected to ammonia heat treatment after ozone treatment, showed higher oxygen and nitrogen contents than carbon felt (J5NH3+O3), which was subjected to ammonia heat treatment first and then ozone treatment. From the charging/discharging of VRFB, the J5O3+NH3 carbon felt electrode showed 14.4 Ah/L discharge capacity at a current density of 150 mA /cm2, which was 15% and 33% higher than that of J5NH3+O3 and non-activated carbon felt (J5), respectively. These results show that ozone and ammonia sequential treatment is an effective carbon felt activation method to increase the performance of the vanadium redox flow battery.

The Role of Vanadium Complexes with Glyme Ligands in Suppressing Vanadium Crossover for Vanadium Redox Flow Batteries

Jungho Lee,Jingyu Park,Kwang-Ho Ha,Hyeonseok Moon,Eun Ji Joo,Kyu Tae Lee The Korean Electrochemical Society 2023 Journal of electrochemical science and technology Vol.14 No.2

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).