This includes studying the resistivity and diffusivity of a microporous separator called Daramic with V4+ ions (Cheing et al., 1992a) and sulfonating an anion exchange membrane to achieve reduction in water transfer in the VRB (Mohammadi et al., 1996). There were also application studies as exemplified by Shibata et al. (1999). This study reported on the development of a vanadium redox battery interconnected to a power plant grid system.
Studies on the different components of the VRFBs to optimize the operations continued in the 2000s which also saw the development of novel VRFBs with improved energy yields (Figure 2). This includes the development of a novel redox flow cell using a polyhalide solution in the half cell catholyte and V2+/V3+ chloride in the half-cell anolyte that yielded an overall cell potential of 1.3V (Skyllas-Kazacos, 2003), a VRFB that showed an energy efficiency of 80.8% at 600 mA/cm2 and was stable for more than 20,000 cycles at 600 mA/cm2 (Jiang et al., 2020), and a VRFB stack consisting of single cells series that showed a steady energy efficiency of 77% during 20 cycles (Li et al., 2024).
Despite the research studies, the year 2021 up till now also had a huge number of review articles on VRFBs analyzing the different components. This includes a review of the 3D electrodes derived from foam, biomass, and electrospun fibers (Ye et al., 2024), a review on the use of metal and carbon-based catalysts by He et al. (2022), and a review of heat generation and heat transfer issues with VRFBs (Ren et al., 2023).
This era also includes the use of life cycle assessment (LCA) methodology to comparatively assess the environmental impact of energy storage batteries including VRFBs. Using the LCA methodology for VRFBs, Lima et al. (2021) reported VRFBs as having a lower environmental impact than lithium batteries when manufactured with recycled electrodes. Moderate environmental impacts have also been reported. For example, L’Abbate et al. (2019) used the LCA methodology on a small scale VRFB and reported that the production of VRFBs have a moderate environmental impact including on vanadium toxicity to human depending on the method used for vanadium electrolyte production.
The vanadium from the VRFB can be recovered as shown by Chen et al. (2022) using ion-exchange column methods that employed resins followed by precipitation and calcination. The purity of the vanadium (V) oxide (V2O5) using this method was over 99%. The ion-exchange resins method is a common method for vanadium recovery compared to other methods used for recycling the purified vanadium electrolyte that is discussed in a comprehensive review by Zuo et al. (2025).
Finally, several studies from the past few years to until recently also used artificial intelligence techniques to optimize the performance of VRFBs. This includes the use of a machine learning model coupled with genetic algorithm to determine its use as a double-layer electrode in a non-aqueous vanadium-iron VRFB (Ma et al., 2023). It also includes the application of the gaussian process regression model to improve VRFB performance and to provide insight into how to use AI in battery design (Talebian et al., 2025).
In the next segment
VRFBs have a complex structure as we saw in segment 1 and yet they are so simple in producing energy as segment 2 showed. They have come a long way since the 1980s from the use vanadium (II), (III), (IV), and (V) in half-cells of redox batteries to the use of artificial intelligence techniques to optimize the performance of VRFBs as shown in this segment. Despite these remarkable advances, this technology like any other technology has also experienced limitations as will be discussed in the next segment.
About the Author: This is the third article in a five-part series on Vanadium Redox Flow Batteries written by Dr. Saleha (Sally) Kuzniewski, Ph.D. Dr. Kuzniewski is a scientist and a writer. In addition to her work at the US Geological Survey on bioremediation and microbial ecology projects and her research in the field of environmental microbiology for the Virginia Department of Game and Inland Fisheries and the Salt Institute, she has also authored several scientific publications including in wastewater treatment and technologies. Dr. Kuzniewski received her BS degree in Biology from William Smith College, Master of Environmental Science degree from Memorial University of Newfoundland, and her Ph.D. degree from George Mason University.
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