Demonstration of the Hydrogen-Vanadium Flow Battery with a Novel High-Energy Storage
Authors: Li Yuanchao , Nguyen Trung 
Published: July 2021

Redox flow battery (RFB) systems such as the all-vanadium, all-iron, and zinc-bromine are gaining significant worldwide interest as an energy storage solution to the increased deployment of intermittent renewable/sustainable energy sources like wind and solar.1 The largest RFB in the world, 200MW/800MWh VRFB, has recently been deployed in Dalian, China.2
Though the RFBs demonstrate many advantages such as the separated scalability of power and energy, being free of the detrimental effects of overcharge, low self-discharge rate, and low cost, its low energy density due to the low solubility of electroactive redox species limits the application of flow battery to the large-scale grid-level energy storage. Taking VRFB as an example, the typical vanadium solubility is in the range of 1.5-2.5M, indicating that most of the storage volume is used for solvent storage (~50M for water).3 Some attempts have been explored in improving the energy density of the flow battery. Skyllas-Kazacos et al. used additives as the stabilizing agents to stabilize the highly supersaturated solution, improving the concentration of vanadium electrolyte to 3M.4 The four vanadium species (+2, +3, +4, +5) may need multiple stabilizing agents. Moreover, the improvement achieved by the stabilized supersaturated solution is not permanent and cannot be further increased. Wang et at. developed a novel type of flow battery based on ferrocyanide and ferricyanide electrolyte, which releases extra ferrocyanide and ferricyanide species from the reaction between Prussian Blue (PB) and Prussian White (PW).5 PB itself occupies volume and requires an integrated crystal structure for the reaction to release ferrocyanide. Thus, the volumetric capacity of [Fe(CN)6]4-/3- is only improved from 40.2 Ah/L to 61.6 Ah/L.
Since the low solubility is the main reason that limits the energy density of the flow battery, to overcome this issue, a new high-energy density approach that i) stores the electroactive species in an aqueous solution and the additional amount of these ions in the precipitate form, ii) circulates only the aqueous part through the flow battery, and iii) releases and restores the electroactive species from the dissolution and precipitation process, was developed by our group.6 A hydrogen-vanadium flow battery, which stored V(IV)/V(V) species in the aqueous/solid hybrid form, was used as the testbed to demonstrate this concept. This presentation will discuss the dissolution/precipitation rate of V(IV)/V(V) cations measured in a static cell. Results from a multiple charge/discharge cycle test of a H2-V flow cell with vanadium concentration up to 3.5M will be showed.
Acknowledgments
This work was also supported by the National Science Foundation under grant number CBET-2024378.
References
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2. M. Huang, B. Hu, D. Li, and S. Xu, ECS Transactions, 89, 15 (2019).
3. C. Ding, H. Zhang, X. Li, T. Liu, and F. Xing, The Journal of Physical Chemistry Letters, 4, 1281–1294 (2013).
4. S. Roe, C. Menictas, and M. Skyllas-Kazacos, Journal of The Electrochemical Society, 163, A5023 (2015).
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6. T. V. Nguyen and Y. Li, University of Kansas, Patent Application No. PCT/US20/61455. November 20, 2020.