Maximizing Vanadium Deployment in Redox Flow Batteries Through Chelation

By tailoring the coordination sphere of vanadium to accommodate a 7-coordinate geometry, a highly soluble (>1.3 M) and reducing (−1.2 V vs Ag/AgCl) flow battery electrolyte is generated from [V­(DTPA)]2–/3– (DTPA = diethylenetriaminepentaacetate). Bulk spectroelectrochemistry is performed in situ to assess material properties in both oxidized and reduced states. Flow batteries are assembled in near neutral pH conditions and operated with discharge energy densities of 12.5 Wh L–1 and high efficiency. Further, the first chelated flow battery using the same aminopolycarboxylate ligand for both electrolytes is generated. The presented batteries demonstrate comparable performance to the iron–vanadium and all-vanadium flow batteries while doubling the effective discharge energy of vanadium (Wh per mol V) and minimizing safety and operating risks, offering grid-scale energy storage alternatives.