ABSTRACT
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, {[(Me3 TACN)Fe][µ-(MoO4 κ3 O,O',O")]}4 (Fe4 Mo4 O16 ). In symmetric battery charging schematics, Fe4 Mo4 O16 facilitates reversible two-electron storage with coulombic efficiencies >99 % over 100â cycles (5â days) with no molecular decomposition and minimal capacity fade. Energy efficiency throughout cycling remained high (â¼82 %), 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.
ABSTRACT
Here, we demonstrate the effects of surface functionalization on a tunable series of nano-sized electron shuttles, toward improving their function in nonaqueous energy storage. The synthesis of a series of polyoxovanadium clusters featuring bridging ether functional groups is reported, revealing the influence of bridging "R" group identity on electrochemical stability in solution. Furthermore, the presence of bridging ether moeities yields enhanced solubility in acetonitrile (up to 1.2 M), highlighting synthetic strategies for the development of organofunctionalized polyoxometalate-derived charge carriers for nonaqueous, electrochemical energy storage.
ABSTRACT
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.
ABSTRACT
Herein we report the synthesis of a series of iron-functionalized, mixed-valent, polyoxovanadate alkoxide clusters, [V5O6(OCH3)12Fe]X (X = Cl, Br, SO3CF3) comprised of a hexanuclear Lindqvist (M6O19(n-)) core. By substituting a VâO moiety from the well-defined hexavanadate clusters [V(IV)nV(V)6-nO7(OR)12](4-n) (R = Me, Et) with a metal cation, we have developed a novel template for investigation of the organometallic properties of these systems. Characterization of the clusters was performed by (1)H NMR, Fourier transform infrared, and electron absorption spectroscopies and electrospray ionization mass spectrometry. The IR and UV-vis spectra suggest substantial electronic delocalization, similar to the previously reported cluster, V6O7(OCH3)12.
