Non-aqueous manganese acetylacetonate electrolyte for redox flow batteries

A single-metal redox flow battery employing manganese(III) acetylacetonate in tetraethylammonium tetrafluoroborate and acetonitrile has been investigated. Cyclic voltammetry was used to evaluate electrode kinetics and reaction thermodynamics. The MnII/MnIII and MnIII/MnIV redox couples appeared to be quasi-reversible. A cell potential of 1.1 V was measured for the one-electron disproportionation of the neutral MnIII complex. The diffusion coefficient for manganese acetylacetonate in the supporting electrolyte solution was estimated to be in the range of 3–5 × 10−6 cm2 s−1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell. Coulombic efficiencies increased with cycling suggesting an irreversible side reaction. Energy efficiencies for this unoptimized system were ∼21%, likely due to the high cell-component overpotentials.

Research highlights
► MnIII/IV, MnII/III and MnI/II couples observed in voltammetry for Mn(acac)3.
► Cell potential of 1.1 V observed for the one-electron disproportionation of Mn(acac)3.
► Diffusion coefficient of Mn(acac)3 in the electrolyte is 3–5 × 10−6 cm2 s−1.
► Coulombic efficiencies increased with cycling.
► Energy efficiencies stable at ∼21% for unoptimized cell.