隨著科技的發展，能源短缺愈發嚴重，因而大型儲能系統將在未來扮演重要的能源供應之角色，全釩液流電池(VRFB)將是一發展重點之一。由於全釩液流電池之石墨氈電極，有著電化學活性不佳、導電性不足之缺點，進而我們想利用低成本之觸媒將其修飾，改善其缺點，並且使其效能提升。
本研究利用導電性佳的還原氧化石墨烯作為無序化之錫酸鈷奈米盒子之載體，並且將其完全裹覆奈米盒之外，透過將兩者之結合提升其催化釩離子之能力。本實驗利用沉澱法將奈米盒複合還原氧化石墨烯，並且利用XRD和TEM確認其結構組成，並能觀察之方形形貌和中空結構，我們利用XPS能譜分析，可以觀察到複合後之氧空位隨之增加，並且將不同樣品進行EPR之分析，可以明顯觀察到複合物之捕捉電子訊號最強。
因此我們進行單電池測試，我們將觸媒修飾於正極石墨氈上，在160 mA/cm2電流密度下，擁有74.22%的伏特效率與熱處理石墨氈相比高出2.69%，在此電流密度下也可明顯觀察出電容量的提升，此外，我們進行五十圈的穩定性測試也並無明顯衰退，方可得知利用錫酸鈷與還原氧化石墨烯之複合物修飾石墨氈可以使效能提升，也可在長時間的循環充、放電下有優異的表現。

With the advancement of technology, energy scarcity has become more severe, leading to the growing importance of large-scale energy storage systems in the future. Vanadium redox flow batteries (VRFBs) will be one of the key developments in this area. However, the graphite felt electrode used in VRFBs suffers from poor electrochemical activity and insufficient conductivity. To address these drawbacks and enhance performance, we aim to modify the graphite felt electrode using a low-cost catalyst.
In this study, we employed highly conductive reduced graphene oxide (rGO) as a carrier for disordered cobalt tin oxide (CoSnO3) nanoboxes. The rGO completely enveloped the nanoboxes to enhance their catalytic capability towards vanadium ions. The nanoboxes-rGO composites were synthesized using a precipitation method, and their structural composition was confirmed using XRD and TEM, revealing a square morphology and hollow structure. XPS analysis showed an increase in oxygen vacancies after composite formation, and EPR analysis of different samples demonstrated the strongest electron capture signal in the composite material.
Subsequently, we conducted single-cell tests by modifying the catalyst onto the positive graphite felt electrode. At a current density of 160 mA/cm², the composite exhibited a voltage efficiency of 74.22%, which was 2.69% higher compared to the thermally treated graphite felt. Significant improvements in capacitance were also observed at this current density. Furthermore, stability testing over 50 cycles showed no significant degradation, indicating that the CoSnO3-rGO modified graphite felt exhibited enhanced performance and excellent performance under long-term cycling of charge and discharge.

1. Varela Soares, I., R. Mauger, and T. Santos, Considerations for benefit stacking policies in the EU electricity storage market. Energy Policy, 2023. 172: p. 113333.
2. Energy statistics - an overview. 2021.
3. <Electricity Energy Storage Technology Options. A White Paper Primer on Applications, Costs, and Benefits.pdf>.
4. Daim, T.U., et al., Evaluation of energy storage technologies for integration with renewable electricity: Quantifying expert opinions. Environmental Innovation and Societal Transitions, 2012. 3: p. 29-49.
5. Lopez-Atalaya, M., et al., Optimization studies on a Fe/Cr redox flow battery. Journal of power sources, 1992. 39(2): p. 147-154.
6. Suresh, S., et al., Zinc–bromine hybrid flow battery: effect of zinc utilization and performance characteristics. RSC Advances, 2014. 4(71): p. 37947-37953.
7. Kabtamu, D.M., et al., The effect of adding Bi 3+ on the performance of a newly developed iron–copper redox flow battery. RSC advances, 2018. 8(16): p. 8537-8543.
8. Sum, E., M. Rychcik, and M. Skyllas-Kazacos, Investigation of the V (V)/V (IV) system for use in the positive half-cell of a redox battery. J. Power Sources;(Switzerland), 1985. 16(2).
9. Sum, E. and M. Skyllas-Kazacos, A study of the V (II)/V (III) redox couple for redox flow cell applications. Journal of Power sources, 1985. 15(2-3): p. 179-190.
10. Guarnieri, M., et al., Vanadium redox flow batteries: Potentials and challenges of an emerging storage technology. IEEE Industrial Electronics Magazine, 2016. 10(4): p. 20-31.
11. Hassan, A. and T. Tzedakis, Enhancement of the electrochemical activity of a commercial graphite felt for vanadium redox flow battery (VRFB), by chemical treatment with acidic solution of K2Cr2O7. Journal of Energy Storage, 2019. 26: p. 100967.
12. Lee, D., et al., A model study on effects of vanadium ion diffusion through ion exchange membranes in a non-aqueous redox flow battery. Journal of Renewable and Sustainable Energy, 2019. 11(3): p. 034701.
13. Yin, C., et al., Numerical and experimental studies of stack shunt current for vanadium redox flow battery. Applied Energy, 2015. 151: p. 237-248.
14. Gattrell, M., et al., The electrochemical reduction of VO2+ in acidic solution at high overpotentials. Electrochimica acta, 2005. 51(3): p. 395-407.
15. Parasuraman, A., et al., Review of material research and development for vanadium redox flow battery applications. Electrochimica Acta, 2013. 101: p. 27-40.
16. Qiu, X., et al., A field validated model of a vanadium redox flow battery for microgrids. IEEE Transactions on Smart grid, 2014. 5(4): p. 1592-1601.
17. Kim, K.J., et al., A technology review of electrodes and reaction mechanisms in vanadium redox flow batteries. Journal of materials chemistry a, 2015. 3(33): p. 16913-16933.
18. Yuan, X.Z., et al., A review of all‐vanadium redox flow battery durability: degradation mechanisms and mitigation strategies. International Journal of Energy Research, 2019. 43(13): p. 6599-6638.
19. Xi, J., et al., Nafion/SiO2 hybrid membrane for vanadium redox flow battery. Journal of Power Sources, 2007. 166(2): p. 531-536.
20. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment. Electrochimica acta, 1992. 37(7): p. 1253-1260.
21. Sun, B. and M. Skyllas-Kazacos, Chemical modification of graphite electrode materials for vanadium redox flow battery application—part II. Acid treatments. Electrochimica Acta, 1992. 37(13): p. 2459-2465.
22. Bayeh, A.W., et al., MoO2–graphene nanocomposite as an electrocatalyst for high-performance vanadium redox flow battery. Journal of Energy Storage, 2021. 40: p. 102795.
23. Bayeh, A.W., et al., Oxygen-vacancy-rich cubic CeO2 nanowires as catalysts for vanadium redox flow batteries. ACS Sustainable Chemistry & Engineering, 2020. 8(45): p. 16757-16765.
24. Kabtamu, D.M., et al., BiVO4-Decorated Graphite Felt as Highly Efficient Negative Electrode for All-Vanadium Redox Flow Batteries. ACS Applied Energy Materials, 2023. 6(6): p. 3301-3311.
25. Bayeh, A.W., et al., Synergistic effects of a TiNb 2 O 7–reduced graphene oxide nanocomposite electrocatalyst for high-performance all-vanadium redox flow batteries. Journal of Materials Chemistry A, 2018. 6(28): p. 13908-13917.
26. Dou, S., et al., Novel amorphous CoSnO3@ rGO nanocomposites highly enhancing sodium storage. Electrochimica Acta, 2019. 316: p. 236-247.
27. Huang, J., et al., 3D graphene encapsulated hollow CoSnO3 nanoboxes as a high initial coulombic efficiency and lithium storage capacity anode. Small, 2018. 14(10): p. 1703513.
28. Dixon, D., et al., Effect of oxygen plasma treatment on the electrochemical performance of the rayon and polyacrylonitrile based carbon felt for the vanadium redox flow battery application. Journal of Power Sources, 2016. 332: p. 240-248.
29. Kabtamu, D.M., et al., Water-activated graphite felt as a high-performance electrode for vanadium redox flow batteries. Journal of Power Sources, 2017. 341: p. 270-279.
30. Jiang, Y., et al., Perovskite enables high performance vanadium redox flow battery. Chemical Engineering Journal, 2022. 443: p. 136341.
31. Hashimoto, T., et al., Analysis of crystal structure and phase transition of LaCrO3 by various diffraction measurements. Solid State Ionics, 2000. 132(3-4): p. 181-188.
32. Bordet, P., et al., Structural aspects of the crystallographic-magnetic transition in LaVO3 around 140 K. Journal of Solid State Chemistry, 1993. 106(2): p. 253-270.
33. Heikes, R., R. Miller, and R. Mazelsky, Magnetic and electrical anomalies in LaCoO3. Physica, 1964. 30(8): p. 1600-1608.
34. Acharya, S., et al., Multiferroic behavior of lanthanum orthoferrite (LaFeO3). Materials Letters, 2010. 64(3): p. 415-418.
35. Noh, C., et al., Effect of the redox reactivity of vanadium ions enhanced by phosphorylethanolamine based catalyst on the performance of vanadium redox flow battery. Journal of Power Sources, 2018. 406: p. 26-34.
36. Wei, L., et al., A high-performance carbon nanoparticle-decorated graphite felt electrode for vanadium redox flow batteries. Applied energy, 2016. 176: p. 74-79.
37. González, Z., et al., Outstanding electrochemical performance of a graphene-modified graphite felt for vanadium redox flow battery application. Journal of Power Sources, 2017. 338: p. 155-162.
38. Guo, S., et al., CoSnO3/C nanocubes with oxygen vacancy as high-capacity cathode materials for rechargeable aluminum batteries. Green Energy & Environment, 2021.
39. Zou, G., et al., N-rich carbon coated CoSnO3derived fromin situconstruction of a Co–MOF with enhanced sodium storage performance. Journal of Materials Chemistry A, 2018. 6(11): p. 4839-4847.
40. Zheng, L., et al., Susceptible CoSnO3 nanoboxes with p-type response for triethylamine detection at low temperature. CrystEngComm, 2020. 22(16): p. 2795-2805.
41. Huang, J., et al., 3D Graphene Encapsulated Hollow CoSnO(3) Nanoboxes as a High Initial Coulombic Efficiency and Lithium Storage Capacity Anode. Small, 2018. 14(10).
42. Wang, Z., et al., Amorphous CoSnO 3@ C nanoboxes with superior lithium storage capability. Energy & Environmental Science, 2013. 6(1): p. 87-91.
43. Zhang, L., Y. Hu, and J. Zheng, Fabrication of 3D hierarchical CoSnO 3@ CoO pine needle-like array photoelectrode for enhanced photoelectrochemical properties. Journal of Materials Chemistry A, 2017. 5(35): p. 18664-18673.
44. Zhao, X., et al., Flexible free-standing ternary CoSnO3/graphene/carbon nanotubes composite papers as anodes for enhanced performance of lithium-ion batteries. Energy, 2017. 118: p. 172-180.
45. Huang, S., et al., Fabrication of multi-layer CoSnO3@ carbon-caged NiCo2O4 nanobox for enhanced lithium storage performance. Chemical Engineering Journal, 2021. 410: p. 128458.
46. Chen, J., et al., Preparation of CoSnO3/CNTs/S and its Electrochemical Performance as Cathode Material for Lithium‐Sulfur Batteries. ChemElectroChem, 2020. 7(20): p. 4209-4217.
47. Fang, G., et al., Facile synthesis of nitrogen-doped carbon coated CoSnO3 via hydrothermal carbonization of carboxylated chitosan as anode materials for lithium-ion batteries. Applied surface science, 2013. 283: p. 963-967.
48. Yue, G., et al., Amorphous CoSnO3@ rGO nanocomposite as an efficient cathode catalyst for long-life Li-O2 batteries. Chinese Journal of Catalysis, 2018. 39(12): p. 1951-1959.
49. Qi, C., C. Zhang, and Z. Yang, Constructing heterointerface of crystalline Au nanoparticles and amorphous porous CoSnO3 nanocubes for sensitive electrochemical detection of glucose. Microchemical Journal, 2022. 183: p. 108039.
50. Cui, W., et al., Nanostructural CoSnC anode prepared by CoSnO3 with improved cyclability for high-performance Li-ion batteries. Electrochimica acta, 2011. 56(13): p. 4812-4818.