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Design and Materials[edit]

Schematic of vanadium redox flow battery.
Solutions of Vanadium sulfates in four different oxidation states of vanadium.

A vanadium redox battery consists of an assembly of power cells in which two electrolytes are separated by a proton exchange membrane.

Electrode[edit]

The electrodes in a VRB cell are carbon based. Several types of carbon electrode used in VRB cell has been report such as carbon felt, carbon paper, carbon cloth, graphite felt, and carbon nanotubes.[1][2][3] Carbon-based materials have the advantages of low cost, low resistivity and good stability. Among them, carbon felt and graphite felt are preferred because of their enhanced three-dimensional network structures and higher specific surface areas, as well as good conductivity and chemical and electrochemical stability.[4][5] The pristine carbon-based electrode exhibits hydrophobicity and limited catalytic activity when interacting with vanadium species. To enhance its catalytic performance and wettability, several approaches have been employed, including thermal treatment, acid treatment, electrochemical modification, and the incorporation of catalysts.[6][7] Carbon felt is typically produced by pyrolyzing polyacrylonitrile (PAN) or rayon fibers at approximately 1500°C and 1400°C, respectively. Graphite felt, on the other hand, undergoes pyrolysis at a higher temperature of about 2400°C. To thermally activate the felt electrodes, the material is heated to 400°C in an air or oxygen-containing atmosphere. This process significantly increases the surface area of the felt, enhancing it by a factor of 10.[8] The activity towards vanadium species are attribute to the increase in oxygen functional groups such as carbonyl group (C=O) and carboxyl group (C-O) after thermal treatment in air.[9] There is currently no consensus regarding the specific functional groups and reaction mechanisms that dictate the interaction of vanadium species on the surface of the electrode. It has been proposed that the V(II)/V(III) reaction follows an inner-sphere mechanism, while the V(IV)/V(V) reaction tends to proceed through an outer-sphere mechanism. [10]

Electrolyte[edit]

Both electrolytes are vanadium-based. The electrolyte in the positive half-cells contains VO2+ and VO2+ ions, while the electrolyte in the negative half-cells consists of V3+ and V2+ ions.

In the early stage of VRFB research, electrolyte was prepared with VOSO4 rather than V2O5 due to the 10 times higher solubility of VOSO4 in sulfuric acid solution than V2O5.[11][12]

The electrolytes can be prepared by several processes, including electrolytically dissolving vanadium pentoxide (V2O5) in sulfuric acid (H2SO4).[13] The solution is strongly acidic in use.

xxxxxxxxxxxxxxx vanadium electrolytes often consist of H2SO4 solutions, sometimes with a small concentration of H3PO4 in order to increase stability [14] xxxxxxxxxxxxxx This ion is believed to occur in solution as the aquo ion [V(H2O)6]2+. VII is a strong reducing agent and it has been reported to be oxidized by water with the evolution of hydrogen. This would suggest that VII should be unstable in aqueous acidic solutions; however, VII is stablized in the presence of sulfate ions.[15]

Membrane[edit]

Flow Field[edit]

The most common membrane material is perfluorinated sulfonic acid (PFSA or Nafion). However, vanadium ions can penetrate a PFSA membrane and destabilize the cell. A 2021 study found that penetration is reduced with hybrid sheets made by growing tungsten trioxide nanoparticles on the surface of single-layered graphene oxide sheets. These hybrid sheets are then embedded into a sandwich structured PFSA membrane reinforced with polytetrafluoroethylene (Teflon). The nanoparticles also promote proton transport, offering high Coulombic efficiency and energy efficiency of more than 98.1 percent and 88.9 percent, respectively.[16]

  1. ^ Mustafa, Ibrahim; Lopez, Ivan; Younes, Hammad; Susantyoko, Rahmat Agung; Al-Rub, Rashid Abu; Almheiri, Saif (March 2017). "Fabrication of Freestanding Sheets of Multiwalled Carbon Nanotubes (Buckypapers) for Vanadium Redox Flow Batteries and Effects of Fabrication Variables on Electrochemical Performance". Electrochimica Acta. 230: 222–235. doi:10.1016/j.electacta.2017.01.186. ISSN 0013-4686.
  2. ^ Mustafa, Ibrahim; Bamgbopa, Musbaudeen O.; Alraeesi, Eman; Shao-Horn, Yang; Sun, Hong; Almheiri, Saif (2017-01-01). "Insights on the Electrochemical Activity of Porous Carbonaceous Electrodes in Non-Aqueous Vanadium Redox Flow Batteries". Journal of the Electrochemical Society. 164 (14): A3673–A3683. doi:10.1149/2.0621714jes. hdl:1721.1/134874. ISSN 0013-4651.
  3. ^ Mustafa, Ibrahim; Al Shehhi, Asma; Al Hammadi, Ayoob; Susantyoko, Rahmat; Palmisano, Giovanni; Almheiri, Saif (May 2018). "Effects of carbonaceous impurities on the electrochemical activity of multiwalled carbon nanotube electrodes for vanadium redox flow batteries". Carbon. 131: 47–59. doi:10.1016/j.carbon.2018.01.069. ISSN 0008-6223.
  4. ^ Chakrabarti, M.H.; Brandon, N.P.; Hajimolana, S.A.; Tariq, F.; Yufit, V.; Hashim, M.A.; Hussain, M.A.; Low, C.T.J.; Aravind, P.V. (May 2014). "Application of carbon materials in redox flow batteries". Journal of Power Sources. 253: 150–166. doi:10.1016/j.jpowsour.2013.12.038.
  5. ^ Singh, Manoj K.; Kapoor, Manshu; Verma, Anil (May 2021). "Recent progress on carbon and metal based electrocatalysts for vanadium redox flow battery". WIREs Energy and Environment. 10 (3). doi:10.1002/wene.393.
  6. ^ He, Zhangxing; Lv, Yanrong; Zhang, Tianao; Zhu, Ye; Dai, Lei; Yao, Shuo; Zhu, Wenjie; Wang, Ling (January 2022). "Electrode materials for vanadium redox flow batteries: Intrinsic treatment and introducing catalyst". Chemical Engineering Journal. 427: 131680. doi:10.1016/j.cej.2021.131680.
  7. ^ Bourke, Andrea; Oboroceanu, Daniela; Quill, Nathan; Lenihan, Catherine; Safi, Maria Alhajji; Miller, Mallory A.; Savinell, Robert F.; Wainright, Jesse S.; SasikumarSP, Varsha; Rybalchenko, Maria; Amini, Pupak; Dalton, Niall; Lynch, Robert P.; Buckley, D. Noel (1 March 2023). "Review—Electrode Kinetics and Electrolyte Stability in Vanadium Flow Batteries". Journal of The Electrochemical Society. 170 (3): 030504. doi:10.1149/1945-7111/acbc99.
  8. ^ Huong Le, Thi Xuan; Bechelany, Mikhael; Cretin, Marc (October 2017). "Carbon felt based-electrodes for energy and environmental applications: A review". Carbon. 122: 564–591. doi:10.1016/j.carbon.2017.06.078.
  9. ^ Parasuraman, Aishwarya; Lim, Tuti Mariana; Menictas, Chris; Skyllas-Kazacos, Maria (July 2013). "Review of material research and development for vanadium redox flow battery applications". Electrochimica Acta. 101: 27–40. doi:10.1016/j.electacta.2012.09.067.
  10. ^ Bourke, Andrea; Oboroceanu, Daniela; Quill, Nathan; Lenihan, Catherine; Safi, Maria Alhajji; Miller, Mallory A.; Savinell, Robert F.; Wainright, Jesse S.; SasikumarSP, Varsha; Rybalchenko, Maria; Amini, Pupak; Dalton, Niall; Lynch, Robert P.; Buckley, D. Noel (1 March 2023). "Review—Electrode Kinetics and Electrolyte Stability in Vanadium Flow Batteries". Journal of The Electrochemical Society. 170 (3): 030504. doi:10.1149/1945-7111/acbc99.
  11. ^ Skyllas‐Kazacos, M.; Grossmith, F. (1 December 1987). "Efficient Vanadium Redox Flow Cell". Journal of The Electrochemical Society. 134 (12): 2950–2953. doi:10.1149/1.2100321.
  12. ^ Choi, Chanyong; Kim, Soohyun; Kim, Riyul; Choi, Yunsuk; Kim, Soowhan; Jung, Ho-young; Yang, Jung Hoon; Kim, Hee-Tak (March 2017). "A review of vanadium electrolytes for vanadium redox flow batteries". Renewable and Sustainable Energy Reviews. 69: 263–274. doi:10.1016/j.rser.2016.11.188.
  13. ^ Guo, Yun; Huang, Jie; Feng, Jun-Kai (February 2023). "Research progress in preparation of electrolyte for all-vanadium redox flow battery". Journal of Industrial and Engineering Chemistry. 118: 33–43. doi:10.1016/j.jiec.2022.11.037.
  14. ^ Skyllas-Kazacos, M.; Chakrabarti, M. H.; Hajimolana, S. A.; Mjalli, F. S.; Saleem, M. (2011). "Progress in Flow Battery Research and Development". Journal of The Electrochemical Society. 158 (8): R55. doi:10.1149/1.3599565.
  15. ^ Skyllas‐Kazacos, Maria; Cao, Liuyue; Kazacos, Michael; Kausar, Nadeem; Mousa, Asem (7 July 2016). "Vanadium Electrolyte Studies for the Vanadium Redox Battery—A Review". ChemSusChem. 9 (13): 1521–1543. doi:10.1002/cssc.201600102.
  16. ^ Lavars, Nick (2021-11-12). "Hybrid membrane edges flow batteries toward grid-scale energy storage". New Atlas. Retrieved 2021-11-14.
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