SCHEDULED MAINTENANCE
Metal acetylacetonate complexes for high energy density non-aqueous redox flow batteries†
Abstract
This paper describes the design, synthesis, and fundamental characterization of a series of Cr and V acetylacetonate (acac) complexes for use in redox flow batteries (RFBs). These materials offer a significant improvement in theoretical energy density relative to state-of-the-art aqueous chemistries. A detailed assessment of the solubility, cyclic voltammetry, and charge–discharge behavior of the complexes is presented. Their solubilities in acetonitrile vary by more than four orders of magnitude based on the structure/substituents on the acac ligand. Complexes bearing acac ligands with ester substituents have solubilities of up to 1.8 M, a significant improvement over most other metal complexes that have been considered for non-aqueous RFB applications. While the acac ligand substituents have a dramatic impact on solubility, they do not, in most cases, impact the electrochemical properties of the complexes. For instance, voltammetry for all of the V(acac)3 derivatives examined exhibit two quasi-reversible redox events separated by approximately 2.1 V. Charge–discharge testing in static H-cell and laboratory-scale flow batteries yielded energy densities that were consistent with the voltammetry and coulombic and energy efficiencies of up to 92% and 87%, respectively. Overall, these studies provide the basis for the development of structure–function relationships that could lead to new and even better performing energy storage chemistries in the future.
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