Carbon materials for the positive electrode in all-vanadium redox flow batteries

Melke, Julia; Jakes, Peter; Langner, Joachim; Riekehr, Lars; Kunz, Ulrike; Zhao‐Karger, Zhirong; Nefedov, Alexei; Sezen, Hikmet; Wöll, Christof; Ehrenberg, Helmut; Roth, Christina

doi:10.1016/j.carbon.2014.06.075

Cited by 87 publications

(61 citation statements)

References 33 publications

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“…Both exchange current density values (Figure a and 4b) suggest that, for the KF and GF types, the reactivity of the positive couple is strongly influenced by the electronic conductivity the carbon fiber. This is highly consistent with observations made by Melke et al . who used near‐edge x‐ray absorption spectroscopy (NEXAFS) and Raman scattering along with electrochemical studies.…”

Section: Resultssupporting

confidence: 91%

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: Resultssupporting

confidence: 91%

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

2017

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“…Because a large increase in surface area is observed with small changes in the oxygen content on the electrode surface, it is concluded that an increase in the surface area, not an increase in the oxygen content, is predominantly responsible for the enhanced kinetic performance. This observation is a departure from other studies in which enhanced kinetics on treated electrode surfaces are attributed to oxygen functional groups [10e14], but agrees with the findings of Melke et al [22]. This disparity suggests that the various treatments may have different mechanisms by which they affect the reaction kinetics for carbon felts as compared to carbon papers.…”

Section: Electrode Characterizationsupporting

confidence: 79%

High performance electrodes in vanadium redox flow batteries through oxygen-enriched thermal activation

Pezeshki

Clement

Veith

et al. 2015

Journal of Power Sources

202

152

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h i g h l i g h t sThermal activation of carbon paper electrodes enhances VRFB kinetic performance. Large increase in surface area is responsible for improved kinetic performance. Significant improvement in depth of charge is achieved. Charge/discharge cycling efficiency of 76% at 200 mA cm À2 is realized. a b s t r a c tThe roundtrip electrochemical energy efficiency is improved from 63% to 76% at a current density of 200 mA cm À2 in an all-vanadium redox flow battery (VRFB) by utilizing modified carbon paper electrodes in the high-performance no-gap design. Heat treatment of the carbon paper electrodes in a 42% oxygen/58% nitrogen atmosphere increases the electrochemically wetted surface area from 0.24 to 51.22 m 2 g À1 , resulting in a 100e140 mV decrease in activation overpotential at operationally relevant current densities. An enriched oxygen environment decreases the amount of treatment time required to achieve high surface area. The increased efficiency and greater depth of discharge doubles the total usable energy stored in a fixed amount of electrolyte during operation at 200 mA cm À2 .

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“…Because drastically different electrode overpotentials were observed for electrodes with similar oxygen content, the results seem to indicate that the oxygen content of the electrode surface does not play a major role in decreasing the electrochemical performance of the carbon materials tested. Melke et al 47 found that heat-treated carbon materials do not rely upon carboxyl or hydroxyl groups to facilitate the vanadium redox reactions. Combined, these results suggest that oxygen groups may not play a significant role in the vanadium redox reactions.…”

Section: Resultsmentioning

confidence: 99%

The Cell-in-Series Method: A Technique for Accelerated Electrode Degradation in Redox Flow Batteries

Pezeshki

Sacci

Veith

et al. 2015

J. Electrochem. Soc.

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We demonstrate a novel method to accelerate electrode degradation in redox flow batteries and apply this method to the all-vanadium chemistry. Electrode performance degradation occurred seven times faster than in a typical cycling experiment, enabling rapid evaluation of materials. This method also enables the steady-state study of electrodes. In this manner, it is possible to delineate whether specific operating conditions induce performance degradation; we found that both aggressively charging and discharging result in performance loss. Post-mortem x-ray photoelectron spectroscopy of the degraded electrodes was used to resolve the effects of state of charge (SoC) and current on the electrode surface chemistry. For the electrode material tested in this work, we found evidence that a loss of oxygen content on the negative electrode cannot explain decreased cell performance. Furthermore, the effects of decreased electrode and membrane performance on capacity fade in a typical cycling battery were decoupled from crossover; electrode and membrane performance decay were responsible for a 22% fade in capacity, while crossover caused a 12% fade. This paper is part of the JES Focus Issue on Redox Flow Batteries-Reversible Fuel Cells.The vanadium redox flow battery (VRFB) is a potential gridscale energy storage technology that has attracted significant research interest.1-5 The cell architecture, electrodes, and membranes have been considerably optimized, resulting in increased efficiency and power density of VRFBs.3,5-10 Other research has focused on improving energy density by enhancing vanadium solubility through the use of additives in the electrolyte solution; these compounds may also enhance electrode activity. [11][12][13] As these improvements continue, the long-term durability of VRFBs becomes an issue with strong implications for commercial viability. Therefore, methods to study component durability are of growing interest.Unlike traditional secondary batteries, VRFBs do not suffer from appreciable unrecoverable capacity fade. They promise to have long lifetimes due to the ability to rebalance the electrolyte, 14-16 which negates capacity fade and may allow them to last for thousands of cycles and for several years. While the vanadium electrolyte is stable, 17 the durability of some components in the VRFB has not been studied in detail. Changes in the electrode can result in increased activation/ charge transfer resistance and decreased mass transport; changes in the membrane may result in increased ohmic resistance in the cell. These phenomena contribute to a decrease in the capacity that can be accessed at high currents as well as to reduced energy efficiency. Herein, we present a methodology and initial findings for studying performance degradation in VRFBs. The energy efficiency loss in a typical VRFB cycling experiment is deconvoluted into contributions from decreased electrode performance and increased ohmic resistance within the membrane. The capacity fade mechanism, often attributed to crossover alone...

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Carbon materials for the positive electrode in all-vanadium redox flow batteries

Cited by 87 publications

References 33 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

High performance electrodes in vanadium redox flow batteries through oxygen-enriched thermal activation

The Cell-in-Series Method: A Technique for Accelerated Electrode Degradation in Redox Flow Batteries

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