Investigation of Cubic Fe 4 M 4 Frameworks for Application in Nonaqueous Energy Storage.

Multimetallic complexes have recently seen increased attention as next-generation charge carriers for nonaqueous redox flow batteries. Herein, we report the electrochemical performance of a molecular iron-molybdenum oxido complex, {[(Me ₃ TACN)Fe][μ-(MoO ₄ κ ³ O,O',O")]} ₄ (Fe ₄ Mo ₄ O ₁₆ ). In symmetric battery charging schematics, Fe ₄ Mo ₄ O ₁₆ facilitates reversible two-electron storage with coulombic efficiencies >99 % over 100 cycles (5 days) with no molecular decomposition and minimal capacity fade. Energy efficiency throughout cycling remained high (∼82 %), as a result of the rapid electron-transfer kinetics observed for each of the complex's four redox events. We also report the synthesis of the analogous synthetic frameworks featuring tungstate vertices or bridging-sulfide moieties, revealing key observations relevant to structure-function relationships and design criteria for these types of heterometallic ensembles.
(© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)