Probing Electrode Losses in All-Vanadium Redox Flow Batteries with Impedance Spectroscopy

Sun, Che-Nan; Delnick, Frank M.; Aaron, Douglas; Papandrew, Alexander B.; Mench, Matthew M.; Zawodzinski, Thomas A.

doi:10.1149/2.001305eel

Cited by 142 publications

(122 citation statements)

References 7 publications

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“…Most studies in the past, however, report overall battery parameters (cell resistance or efficiency) and hence conclude with rather general statements. More detailed investigations using reference electrodes or non‐symmetric felt combinations at the positive and negative electrodes have shown that the negative electrode is more problematic with respect to the kinetic overpotential. In fact, recent systematic studies of the electrochemical pretreatment of various carbons (glassy carbon, carbon fibers, graphite) have even revealed opposing effects for both redox couples when subjected to anodic or cathodic pre‐treatment .…”

Section: Introductionmentioning

confidence: 99%

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

2017

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Carbon felts based on rayon and polyacrylonitrile (PAN) precursors constitute the most widespread porous electrode material for vanadium redox‐flow batteries. Since the raw materials exhibit rather poor wettability, it has become common practice to apply oxidative surface treatments prior to use in flow batteries. This study investigates the electrode‐specific effects of raw and thermally oxidized (PAN and rayon‐based) carbon felts on their electrochemical behavior at the negative and the positive electrode in all vanadium redox‐flow batteries. By means of steady‐state single cell measurements, it is verified that oxidative surface treatment has opposite effects on negative and positive redox couples and that the beneficial influence on the vanadium redox‐flow battery performance is mainly brought about by substantially improved charge‐transfer kinetics at the negative electrode. Similarly, the type of carbon precursor and the degree of graphitic character have a particular impact on the electrode behavior.

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Section: Introductionmentioning

confidence: 99%

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

2017

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“…Carbon materials, and carbon felts in particular, are conventionally used in VRFB electrodes. The slow rates of these reactions are a serious problem in VRFB technology, which must be solved to improve the efficiency of VRFBs . We found that a 3D RGO network was successfully formed in a loosely entangled carbon‐fiber matrix and that the activity for the vanadium redox reactions was correlated to the network structure.…”

Section: Introductionmentioning

confidence: 99%

Vanadium‐Ion Redox Reactions in a Three‐Dimensional Network of Reduced Graphite Oxide

et al. 2016

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A three‐dimensional (3D) fine network structure of thin carbon microflakes inside a loosely entangled carbon‐fiber matrix was formed by applying an ice‐template method to a graphite oxide (GO) dispersion in the matrix and thermal reduction of the GO. Vanadium‐ion redox reactions were investigated in the network of reduced GO (RGO) for potential application as electrodes in vanadium redox flow batteries (VRFB). The development of the fineness, the degree of graphitization, the structural disorder, and the surface composition were characterized. The interaction between the carbon surface species and the vanadium ions was implied by the X‐ray absorption fine structure (XAFS). The structure of the 3D RGO network was clearly correlated to the activity for the VRFB positive electrode reactions, and the development of the fine network structure effectively enhanced the reactions due to increased exposure of the edge planes and sufficient dispersion of the active sites.

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“…[3][4][5] Two promising technologies are the all-vanadium RFB (VRB) and the hydrogen/bromine RFB, where good performances have been demonstrated recently. [6][7][8][9][10][11][12][13][14] Protons in a cation-exchange membrane (CEM) typically carry charge between the two electrodes in these two RFBs. In both systems, movement of reactant or product species from one electrode to the other through the membrane results in inefficiency and reversible capacity loss.…”

mentioning

confidence: 99%

The Influence of Electric Field on Crossover in Redox-Flow Batteries

Darling

Weber

Tucker

et al. 2015

J. Electrochem. Soc.

152

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Transport of active species through the ion-exchange membrane separating the electrodes in a redox-flow battery is an important source of inefficiency. Migration and electro-osmosis have significant impacts on the crossover of reactive anions, cations, and neutral species. In this paper, these phenomena are theoretically and experimentally explored for commercial cation-exchange membranes. The theoretical analysis indicates that plotting the cumulative Coulombic mismatch between charge and discharge as a function of time can be used to assess crossover rates. The relative importance of migration and electro-osmosis over diffusion is quantified and shown to increase with increasing current density and membrane thickness because the contributions of migration and electro-osmosis to ionic flux are independent of membrane thickness and proportional to current density, while diffusion is inversely proportional to membrane thickness and independent of current density. Redox-flow batteries (RFBs) possess compelling attributes for stationary energy storage. In particular, the inherent decoupling of energy and power in RFBs enables the cost effective use of active materials with low energy density.1,2 Energy is stored in redox-active molecules and power is generated by oxidizing and reducing different redox couples at the positive and negative electrodes.3-5 Two promising technologies are the all-vanadium RFB (VRB) and the hydrogen/bromine RFB, where good performances have been demonstrated recently. [6][7][8][9][10][11][12][13][14] Protons in a cation-exchange membrane (CEM) typically carry charge between the two electrodes in these two RFBs. In both systems, movement of reactant or product species from one electrode to the other through the membrane results in inefficiency and reversible capacity loss. 8,15,16 For these reasons it is worthwhile to investigate the causes of crossover, and examination of the two chosen RFBs allows for the study of transport of active cations, anions, and neutral species.The reactions at the negative and positive electrodes in a VRB are:andrespectively. Protons are the primary ionic charge carriers. Because the active species at both electrodes are vanadium ions, transfer from one electrode to the other is less detrimental than it is in other RFBs that have dissimilar active materials at the two electrodes. Vanadium that traverses the separator reacts to form a discharged ion at the opposite electrode. 17 Although imbalances that occur after repeated cycling can be recovered by mixing the electrolytes, vanadium that crosses the membrane represents an inefficiency that is detrimental in applications like grid-scale energy storage where high efficiency is required for economic success.For the hydrogen/bromine RFB, the reactions at the negative and positive electrodes areBr 2 (aq) + 2e 18-21 Br species that enter the negative electrode can be separated from the negative electrolyte and returned to the positive electrolyte without causing permanent decay, in a similar fashion to vanadium in V...

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Probing Electrode Losses in All-Vanadium Redox Flow Batteries with Impedance Spectroscopy

Cited by 142 publications

References 7 publications

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

Vanadium‐Ion Redox Reactions in a Three‐Dimensional Network of Reduced Graphite Oxide

The Influence of Electric Field on Crossover in Redox-Flow Batteries

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