Jump to main content
Jump to site search


Predicting the Potentials, Solubilities and Stabilities of Metal-Acetylacetonates for Non-Aqueous Redox Flow Batteries Using Density Functional Theory Calculations

Abstract

(RFBs) for grid-scale energy storage applications. Efforts to develop better performing materials, which have largely been empirical, would benefit from a better understanding of relationships between structural, electronic and RFB-relevant functional properties. This paper focuses on metal-acetylacetonates, a class of metal coordination complexes that has shown promise for use in RFBs, and describes correlations between their experimentally measured standard potentials, solubilities, and stabilities (cycle lifes), and selected chemical, structural and electronic properties determined from Density Functional Theory (DFT) calculations. The training set consisted of 16 complexes including 5 different metals and 11 different substituents on the acetylacetonate ligand. Standard potentials through five oxidation states were computed using the full thermodynamic cycle. The oxidation and reduction potentials also correlated with the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, respectively. These correlations allow for determination of the standard potentials from easily calculated properties of the neutral species. A predictive equation based on the solvation energies and dipole moments, two easily computed properties, reasonably modeled the experimentally determined solubilities. The influence of the solvation energy was expected and the dipole moment accounts for the importance of polarity. Importantly, we were able to identify a descriptor for the stability of acetylacetonates. Experimentally determined stabilities, quantified as the cycle life to a given degree of degradation, correlated with the percentage of the HOMO or LUMO on the metal of the complex. This percentage is influenced by the degree of ligand innocence (irreducibility), and complexes with the most innocent ligands yielded the most stable redox reactions. To this end, VO(acac)2 and Fe(acac)3, with nearly 80% of the HOMO and LUMO on the metal, possessed the most stable oxidation and reduction half-reactions, respectively. The structure-function relationships and correlations presented in this paper could be used to predict new, highly soluble and stable complexes for RFB applications.

Back to tab navigation
Please wait while Download options loads

Supplementary files

Publication details

The article was received on 10 Feb 2017, accepted on 19 May 2017 and first published on 19 May 2017


Article type: Paper
DOI: 10.1039/C7TA01285C
Citation: J. Mater. Chem. A, 2017, Accepted Manuscript
  •   Request permissions

    Predicting the Potentials, Solubilities and Stabilities of Metal-Acetylacetonates for Non-Aqueous Redox Flow Batteries Using Density Functional Theory Calculations

    J. F. Kucharyson, L. Cheng, S. O. Tung, L. A. Curtiss and L. Thompson, J. Mater. Chem. A, 2017, Accepted Manuscript , DOI: 10.1039/C7TA01285C

Search articles by author