Investigation of Cubic Fe₄M₄ Frameworks for Application in Nonaqueous Energy Storage

Abstract

Multimetallic complexes have recently seen increased attention as next-generation chargec arriers forn onaqueous redox flow batteries. Herein, we report the electrochemical performance of am olecular iron-molybdenum oxido complex, {[(Me 3 TACN)Fe][m-(MoO 4 k 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 %o ver1 00 cycles (5 days) with no molecular decomposition and minimal capacity fade.Energy efficiency throughout cycling remainedh igh (~82 %), as ar esult of the rapid electron-transfer kinetics observed for each of the complex'sf our redox events. We also report the synthesiso ft he analogouss ynthetic frameworks featuring tungstate vertices or bridging-sulfide moieties, revealing key observations relevant to structure-function relationships and design criteria for theset ypes of heterometallic ensembles.

A Comparative Review of Metal‐Based Charge Carriers in Nonaqueous Flow Batteries

“…[a] Charge carrier Redox potential vs. Ag/Ag decreased from 60 to % after 20 cycles due to membrane degradation. Matson and co-workers [65] prepared Fe 4 Mo O 16 , which also exhibits a cubic structure and stable cycling behavior over 100 cycles (EE = 82 %).…”

“…Modrzynski and Burger [64] drew inspiration from nature when they developed the cubic Fe 4 S 4 (Stfe) 4 ionic liquid negolyte, which has a maximum theoretical energy density of 87.7 Wh L À 1 and a redox potential of À 1.69 V. The complex was investigated up to 1 m at 50 °C to decrease viscosity and achieved an energy density of 43.6 Wh L À 1 , although EE [a] TRIS: tris(hydroxymethyl)methane; Stfe: trifluoroethanethiolate decreased from 60 to 40 % after 20 cycles due to membrane degradation. Matson and co-workers [65] prepared Fe 4 Mo 4 O 16 , which also exhibits a cubic structure and stable cycling behavior over 100 cycles (EE = 82 %). The solubility of the complex is below 1 mm in MeCN, however, limiting the theoretical energy density of the system.…”