Cost, Performance, and Sustainability of Redox Flow Batteries Using 4,5-Dihydroxy-1,3-benzenedisulfonic Acid and Vanadium Enhanced by Cross Compensation of the Activation Process

Vanadium redox flow batteries (VRFBs) receive attention as a promising energy storage device due to high efficiency and excellent long-term durability although vanadium ore is expensive. To address this price issue, cheap quinone RFBs (QRFBs) using anthraquinone-2,7-disulfonic acid and 4,5-dihydroxy-1,3-benzenedisulfonic acid (tiron) are introduced. However, QRFBs require additional activation process of tiron. To alleviate the issues of VRFBs and QRFBs, new RFBs using vanadium and tiron as the anolyte and catholyte are suggested. This redox couple can exchange their activation process mutually. Thus, additional electrolytes are not needed, saving the considerable amount of active materials. Regarding performance, cell voltage of the new RFBs (1.2 V) is higher than that of QRFBs (0.76 V), while their capacity retention (decay rate of 0.044% cycle^-1) is better than that of VRFBs (decay rate of 0.12% cycle^-1). Bismuth-based catalysts further increase the energy density of new RFBs because they promote the reactivity of V²⁺/V³⁺ redox reaction. Even in economic prospect, cost-normalized discharge energy density of new RFBs (0.98 Wh L^-1 $^-1) is better than that of VRFBs (0.75 Wh L^-1 $^-1) and QRFBs (0.15 Wh L^-1 $^-1), confirming that RFBs using vanadium and tiron have benefits regarding cost, stability, and performance.