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) , to vanadium acetylacetonate, V(acac) , is introduced. V(acac) has been studied for use in redox flow batteries (RFBs) for some time; however, contamination by moisture leads to the formation of VO(acac) . 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) during 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., V /V and V /V redox couples) per V ion to increase the energy density of RFBs becomes possible owing to the in situ recovery of V(acac) during discharge. The concept of in situ recovery of material can lead to more advances in maintaining the cycle life of RFBs in the future.

3D Graphene–Ni Foam as an Advanced Electrode for High-Performance Nonaqueous Redox Flow Batteries

“…Given the unique operating mechanism of RFBs, both the electrolytes that govern the electrochemical redox reactions and the electrodes must be chosen carefully to achieve high-energy-efficiency RFBs; , the electrodes must be robust and offer sufficient reaction sites. To this end, intensive efforts have been devoted to developing nonaqueous electrolytes that exhibit higher operating voltages (>2 V) than aqueous electrolytes, which are limited to an operating voltage of less than 1.7 V due to water hydrolysis. − However, only a few studies have investigated metal electrodes as replacements for commercial carbon felt electrodes …”

“…Recently, the feasibility of using metal-foam electrodes in nonaqueous RFBs has been examined. ,, Although using metal-foam electrodes can improve the electrochemical reactivity of RFBs, additional surface modifications such as carbon coating and chemical etching are still necessary to generate sufficient reaction sites due to their low specific surface area. Nevertheless, using metal-foam electrodes still holds great promise because of their excellent mechanical stability, low specific resistance, porous structure, and cheaper price than carbon-based electrode in this research field. − …”

Metal Acetylacetonate–Bidentate Ligand Interaction (MABLI) (Photo)activated Polymerization: Toward High Performance Amine-Free, Peroxide-Free Redox Radical (Photo)initiating Systems

“…The commercial V(acac) 3 complex is indeed V(III) as confirmed using highresolution electrospray ionization mass spectrometry (HR-ESI-MS, Table S1); some residual V(IV) can be present in vanadium acetylacetonate as previously reported. 53,54 In the ESR-ST experiment without light (Figure 4A), no radicals were trapped at all using PBN. After gradual LED@405 nm irradiation times (60 and 180 s, Figure 4A), a Ph • /PBN radical adduct 28 can be observed as simulation fitted well experimental curve (Figure 4B) using the following hyperfine splitting constants: a N = 14.5 G and a H = 2.5 G.…”

A High Capacity, Room Temperature, Hybrid Flow Battery Consisting of Liquid Na-Cs Anode and Aqueous NaI Catholyte

“…Recently, another concept of hybrid flow batteries with a molten Na-Cs alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane and operated at room temperature has been proposed [39][40][41]. This hybrid Na-based flow battery (HNFB), as shown schematically in Figure 1, has the potential to offer many unmatched advantages over VRBs.…”

“…Schematic of a hybrid Na-based flow battery (HNFB) with a floating Na-Cs anode on the Na-ion exchange membrane and a flowing catholyte, operated at room temperature[39][40][41].…”