title: New Mechanism for the Reduction of Vanadyl Acetylacetonate to Vanadium Acetylacetonate for Room Temperature Flow Batteries.
abstract: In this study, a new mechanism for the reduction of vanadyl acetylacetonate, VO(acac)2, to vanadium acetylacetonate, V(acac)3, is introduced. V(acac)3has been studied for use in redox flow batteries (RFBs) for some time; however, contamination by moisture leads to the formation of VO(acac)2. In previous work, once this transformation occurs, it is no longer reversible because there is a requirement for extreme low potentials for the reduction to occur. Here, we propose that, in the presence of excess acetylacetone (Hacac) and free protons (H+), the reduction can take place between 2.25 and 1.5 V versus Na/Na+via a one-electron-transfer reduction. This reduction can take place in situ during discharge in a novel hybrid Na-based flow battery (HNFB) with a molten Na-Cs alloy as the anode. The in situ recovery of V(acac)3during discharge is shown to allow the Coulombic efficiency of the HNFB to be ≈100 % with little or no capacity decay over cycles. In addition, utilizing two-electron-transfer redox reactions (i.e., V3+/V4+and V2+/V3+redox couples) per V ion to increase the energy density of RFBs becomes possible owing to the in situ recovery of V(acac)3during discharge. The concept of in situ recovery of material can lead to more advances in maintaining the cycle life of RFBs in the future.
authors.affiliation: Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, Illinois, 60616, USA.
authors.forename: Jack S
authors.initials: JS
authors.lastname: Shamie
authors.affiliation: Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, Illinois, 60616, USA.
authors.forename: Caihong
authors.initials: C
authors.lastname: Liu
authors.affiliation: Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, Illinois, 60616, USA.
authors.forename: Leon L
authors.initials: LL
authors.lastname: Shaw
authors.affiliation: Energy Storage and Conversion Energy Materials, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Sprenkle
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D011211:Electric Power Supplies; D004563:Electrochemistry; D006885:Hydroxybutyrates / Q000737:chemistry*; D010084:Oxidation-Reduction; D010422:Pentanones / Q000737:chemistry*; D013696:Temperature; D014639:Vanadium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D006885:Hydroxybutyrates; D010422:Pentanones; D014639:Vanadium; C049529:acetyl acetonate
keywords: ambient temperature; flow batteries; non-aqueous catholyte; sodium; vanadium acetylacetonate