Organic Functionalization of Polyoxovanadate-Alkoxide Clusters: Improving the Solubility of Multimetallic Charge Carriers for Nonaqueous Redox Flow Batteries.

The success of nonaqueous redox flow battery technology requires synthetic advances in charge carrier design to increase compatibility with organic solvents. Herein, previous discoveries related to the development of multimetallic charge carriers are built upon with the high-yielding syntheses of ether- functionalized polyoxovanadate-alkoxide clusters, [V6 O7 (OR)9 (OCH2 )3 CR'] (R=CH3 , C2 H5 ; R'=CH3 , CH2 OCH3 , CH2 OC2 H4 OCH3 ). Like their homoleptic congeners [V6 O7 (OR)12 ] (R=CH3 , C2 H5 ), these clusters exhibit four redox events, spanning nearly a two-volt window, and demonstrate rapid electron-transfer kinetics. The ethoxide derivatives can reversibly cycle two electrons at each electrode in symmetric charging schematics, demonstrating long-term solution stability. Furthermore, ether functionalization yields a twelvefold increase in solubility, a factor which directly dictates the energy density of a redox flow battery.