Electrode kinetics in non-aqueous vanadium acetylacetonate redox flow batteries

Shinkle, Aaron A.; Sleightholme, Alice E.S.; Thompson, Levi T.; Monroe, Charles W.

doi:10.1007/s10800-011-0314-z

Cited by 79 publications

(59 citation statements)

References 28 publications

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“…12 The model from that study is based on an assumption that the metal complex undergoes an outersphere, single-electron disproportionation, i.e., it identifies the redox events on either side of the OCP with a [V(acac) 3 ] 0/+1 couple (at 0.45 V vs. Ag/Ag + ) and a [V(acac) 3 ] -1/0 couple (at -1.77 V Vs. Ag/Ag + ). As discussed by Shinkle et al, 12 the microelectrode LSV response of a complex that disproportionates electrochemically differs from traditional LSV experiments that probe isolated half-reactions. During microelectrode LSV of disproportionation complexes, current is expected to be near zero at the OCP of the pristine solution, and nonzero currents are observed at the equilibrium potentials of the positive and negative couples involved in the disproportionation.…”

Section: Voltammetry Resultsmentioning

confidence: 99%

“…Linear-sweep voltammetry (LSV) experiments with microelectrodes, similar to those performed by Shinkle et al 12 with V(acac) 3 solutions, show that the redox activity of Cr(acac) 3 is inconsistent with a single-electron disproportionation mechanism: there appears to be a charge imbalance between the first oxidation and the first reduction half-reactions. Spectroelectrochemistry supports the previously proposed simple outer-sphere mechanism for V(acac) 3 , while experiments with Cr(acac) 3 provide evidence of ligand dissociation during the first reduction.…”

mentioning

confidence: 78%

“…Consequently, Reaction 1 is expected to produce free acac − as a reaction product. The increased complexity of this electrochemical reaction renders examination of microelectrode LSV data by the method used for V(acac) 3 LSV 12 uninformative, since the model for vanadium redox kinetics assumes that the first oxidation and first reduction are both singleelectron outer-sphere reactions. Additionally, the formation of acetylacetonate products during Reaction 1 suggests that its reverse involves several species, which could include the electrode, chromium coordination complexes in various forms with various redox states, and the free ligand.…”

Section: -34mentioning

confidence: 99%

“…The Cr(acac) 3 complex has also been used for catalysis 10 and as a standard for atomic absorption spectra. 11 Whereas vanadium acetylacetonate, or V(acac) 3 , appears to support outer-sphere electron transfer for both single-electron addition and withdrawal in certain nonaqueous electrolytes, and to undergo both charge exchanges with relatively facile kinetics, 12 the voltammetric response of Cr(acac) 3 is harder to interpret. Experimental efforts to clarify the electrochemistry of Cr(acac) 3 have been challenging because the reaction mechanism apparently varies with the choices of solvent, supporting electrolyte, and working electrode.…”

mentioning

confidence: 99%

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Spectroelectrochemistry of Vanadium Acetylacetonate and Chromium Acetylacetonate for Symmetric Nonaqueous Flow Batteries

Saraidaridis

Bartlett

Monroe

2016

J. Electrochem. Soc.

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Chromium acetylacetonate, or Cr(acac) 3 , is a promising active species for high-energy-density symmetric redox flow batteries because the neutral complex supports multiple charge-transfer reactions with widely separated redox potentials. Voltammetric and spectroelectrochemical measurements were performed to probe the mechanism of the first electrochemical disproportionation of Cr(acac) 3 -i.e., the cell reaction associated with the two redox couples immediately adjacent to the equilibrium potential of a freshly prepared nonaqueous Cr(acac) 3 solution. Substantially different limiting currents are observed for the positive and negative half-reactions, suggesting that at least one deviates from the similar outer-sphere single-electron transfer mechanisms proposed earlier. Spectroelectrochemical chronoamperometry suggests ligand dissociation in the negative reaction, and consequent structural reorganization of the Cr(acac) 3 complex. Vanadium acetylacetonate was investigated for comparison, and no ligand dissociation was observed. A negative half-reaction mechanism consistent with the voltammetric and spectroelectrochemical data is proposed, and used to rationalize observations of charge/discharge behavior in cycling Cr (acac) As researchers have identified the economic benefits that largescale energy storage delivers to the grid, research into redox flow batteries (RFBs) has expanded.1 In efforts to increase energy density or decrease active-species loading, researchers have targeted nonaqueous RFB chemistries, which can produce operating potentials outside the stability window of water.2-8 Several nonaqueous chemistries are based on transition-metal-centered coordination complexes. 2,3,[6][7][8][9] Chromium acetylacetonate, or Cr(acac) 3 , appears especially promising as an RFB active species: it has five accessible redox states, and there is a wide voltage separation between the first reduced and first oxidized states of the neutral complex. The Cr(acac) 3 complex has also been used for catalysis 10 and as a standard for atomic absorption spectra.11 Whereas vanadium acetylacetonate, or V(acac) 3 , appears to support outer-sphere electron transfer for both single-electron addition and withdrawal in certain nonaqueous electrolytes, and to undergo both charge exchanges with relatively facile kinetics, 12 the voltammetric response of Cr(acac) 3 is harder to interpret. Experimental efforts to clarify the electrochemistry of Cr(acac) 3 have been challenging because the reaction mechanism apparently varies with the choices of solvent, supporting electrolyte, and working electrode. 13-17The literature describing nonaqueous Cr(acac) 3 electrochemistry does not provide a consensus about the mechanisms for either the first reduction or first oxidation of the neutral complex. The electrochemical response during reduction depends heavily upon solvent, with different behavior observed in dimethylsulfoxide, 13,15,18,19 N,N-dimethylformamide, 15 dichloromethane, 14 acetonitrile, 15,17,20 and others. 15 Various mechanisms have...

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Section: Voltammetry Resultsmentioning

confidence: 99%

mentioning

confidence: 78%

Section: -34mentioning

confidence: 99%

mentioning

confidence: 99%

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Spectroelectrochemistry of Vanadium Acetylacetonate and Chromium Acetylacetonate for Symmetric Nonaqueous Flow Batteries

Saraidaridis

Bartlett

Monroe

2016

J. Electrochem. Soc.

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“…The formal cell potential of the V(acac) 3 system is 2.2 V which is associated with the single-electron disproportionation of V(acac) 3 by the redox reactions of the V(III)/V(II) couple at the negative electrode and the V(III)/V(IV) couple at the positive electrode as follows: 7,22 [V (III) (acac) 3 …”

mentioning

confidence: 99%

Performance of a Non-Aqueous Vanadium Acetylacetonate Prototype Redox Flow Battery: Examination of Separators and Capacity Decay

Escalante-García

Wainright

Thompson

et al. 2014

J. Electrochem. Soc.

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126

119

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Non-aqueous electrolytes are stable over wide electrochemical potential windows, generally >2 V, and therefore hold promise for enabling higher energy and power density redox flow batteries (RFBs). Nevertheless, the development of non-aqueous RFBs is at an early stage and significant research efforts are needed to demonstrate non-aqueous RFBs with performance characteristics that exceed those of aqueous RFBs. The membrane or separator is a critical component that to a great extent determines the performance of RFB systems for practical applications. In this work, the performance of a RFB was evaluated with Nafion 1035 membranes and Daramic 175 SLI microporous separators. The non-aqueous electrolyte was based on vanadium (III) acetylacetonate. This chemistry possesses two couples over ∼2.2 V. Charge-discharge cycles were performed in a RFB at a current density of 10 mA cm −2 . Coulombic and energy efficiencies of 91% and 80% were achieved using the Nafion membrane. A similar RFB using the Daramic microporous separator achieved columbic and energy efficiencies of 73% and 68%, respectively. The source of capacity decay during multiple charge-discharge cycles was also investigated. The loss in the capacity was related to the poor chemical stability of the vanadium acetylacetonate in the positive electrolyte during battery cycling. Redox flow batteries (RFBs) have emerged as very attractive options for large-scale energy storage applications and, could facilitate the integration of renewable energy resources (e.g. wind and solar) with the current electricity grid.1,2 RFBs are electrochemical devices that store electrical energy in soluble electro-active species in a liquid electrolyte. The electro-active species are stored externally in separate reservoirs and are pumped through the battery stack during operation. The energy is stored or delivered by means of a redox reaction between the two species with different standard electrode potentials, separated by a membrane.2,3 Unlike conventional batteries, RFBs are more attractive for large scale energy storage because they offer more flexible operation, simple electrode reactions, longer cycle life, higher overall energy efficiencies and easier scale-up. 4 Nonetheless, RFB technology is still in an early stage; challenges that remain in the quest to produce devices with high power and energy density at low cost include the discovery or development of stable, high energy density redox electrolytes, and efficient and low cost membranes or separators. 1,5 Aqueous and non-aqueous chemistries are being investigated for use in RFBs. The cell potential of aqueous RFBs is limited to less than ∼1.6 V primarily due to the electrochemical stability of water at carbon/graphite electrodes.6 Non-aqueous solvents, on the other hand, exhibit wider electrochemical potential windows, offering the possibility for higher power and energy densities. Several non-aqueous electrolytes using metal-ligand complexes as the active-redox species in organic solvents have exhibited cell potentials ab...

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Modeling and Simulation of Flow Batteries

Esan

Shi

Pan

et al. 2020

Advanced Energy Materials

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Flow batteries have received extensive recognition for large‐scale energy storage such as connection to the electricity grid, due to their intriguing features and advantages including their simple structure and principles, long operation life, fast response, and inbuilt safety. Market penetration of this technology, however, is still hindered by some critical issues such as electroactive species crossover and its corresponding capacity loss, undesirable side reactions, scale‐up and optimization of structural geometries at different scales, and battery operating conditions. Overcoming these remaining challenges requires a comprehensive understanding of the interrelated structural design parameters and the multivariable operations within the battery system. Numerical modeling and simulation are effective tools not only for gaining an understanding of the underlying mechanisms at different spatial and time scales of flow batteries but also for cost‐effective optimization of reaction interfaces, battery components, and the entire system. Here, the research and development progress in modeling and simulation of flow batteries is presented. In addition to the most studied all‐vanadium redox flow batteries, the modelling and simulation efforts made for other types of flow battery are also discussed. Finally, perspectives for future directions on model development for flow batteries, particularly for the ones with limited model‐based studies are highlighted.

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Electrode kinetics in non-aqueous vanadium acetylacetonate redox flow batteries

Cited by 79 publications

References 28 publications

Spectroelectrochemistry of Vanadium Acetylacetonate and Chromium Acetylacetonate for Symmetric Nonaqueous Flow Batteries

Spectroelectrochemistry of Vanadium Acetylacetonate and Chromium Acetylacetonate for Symmetric Nonaqueous Flow Batteries

Performance of a Non-Aqueous Vanadium Acetylacetonate Prototype Redox Flow Battery: Examination of Separators and Capacity Decay

Modeling and Simulation of Flow Batteries

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