An Organic Electroactive Material for Flow Batteries

An inexpensive, abundant electroactive organic molecule, 3,4-Dihydroxy-9,10-anthraquinone-2-sulfonic acid (ARS) is proposed to serve as the redox active material in the negative side of flow batteries. The electrochemical characteristics and mass transport properties are discussed in this work. The diffusion coefficient of ARS is calculated as 2.14 × 10^-6 cm² s^-1, and the kinetic rate constant of ARS is further measured as 3.6 × 10^-3 cm s^-1, which is faster than other metal redox active species used in flow batteries, such as Fe³⁺/Fe²⁺, Cr³⁺/Cr²⁺, VO₂⁺/VO²⁺, and Ce⁴⁺/Ce³⁺. Unlike metal redox materials, ARS will not suffer from the resource constraints. Combining 1,2-benzoquinone-3,5-disulfonic acid (BQDS) as the positive electroactive species and H₂SO₄ solution as the supporting electrolyte, the different charging-discharging behavior and the polarization curves exhibited a good performance with our laboratory design flow cell. It can be concluded that the ARS presents a unique opportunity for developing a promising and cost-effective alternative for metal-free flow batteries.