Impact of Surface Carbonyl- and Hydroxyl-Group Concentrations on Electrode Kinetics in an All-Vanadium Redox Flow Battery

Li, Yue; Parrondo, Javier; Sankarasubramanian, Shrihari; Ramani, Vijay

doi:10.1021/acs.jpcc.8b11874

Cited by 60 publications

(55 citation statements)

References 65 publications

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“…[1][2][3] It is widely accepted that OFGs work as an effective catalyst towards the occurring redox reactions in a vanadium flow battery (VFB). [4][5][6][7] This has sparked a lot of scientific as well as industrial activities, which focus on the optimization of the carbon-based electrodes by various oxidative treatments. Several surface treatment methods have been reported to increase the activity of the felt electrode by employing OFGs using thermal, chemical, electrochemical, acid or alkaline activation.…”

Section: Introductionmentioning

confidence: 99%

“…For many electrochemical applications that utilize graphitic materials such as batteries, electrolyzers, or supercapacitors, surface‐active oxygen functional groups (OFGs) at the electrode are considered essential [1–3] . It is widely accepted that OFGs work as an effective catalyst towards the occurring redox reactions in a vanadium flow battery (VFB) [4–7] . This has sparked a lot of scientific as well as industrial activities, which focus on the optimization of the carbon‐based electrodes by various oxidative treatments.…”

Section: Introductionmentioning

confidence: 99%

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Influence and Electrochemical Stability of Oxygen Groups and Edge Sites in Vanadium Redox Reactions

et al. 2020

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It is widely accepted that surface-active oxygen functional groups (OFGs) effectively catalyze the vanadium redox reactions. Initial graphitic edge sites, OFGs and their electrochemical stability were examined using graphite felts, which were modified with multi-walled carbon nanotubes and activated with KOH. It is demonstrated that OFGs cannot exclusively be responsible for the electrocatalysis since they did not correlate to the electrochemical activity. The surface composition after electrochemical cycling in the positive half-cell was still different for all samples but did not reflect the performance either. However, a correlation was found between the activity and stable edge site defects. There was neither a correlation between the electrocatalytic activity and the amount of oxygen, nor for the kind of OFG in the negative half-cell. The oxygen concentration after electrochemistry was very similar, even more highlighting the importance of edge sites in the V III /V II redox reaction. The results of this work indicate that the major electrocatalytic effect for both half-cell redox reactions is related to stable graphitic edge sites in sufficient quantity.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influence and Electrochemical Stability of Oxygen Groups and Edge Sites in Vanadium Redox Reactions

et al. 2020

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“…A recent attempt was made to sort out these inconsistencies by employing rotating disk electrode techniques on thermally treated carbon electrodes. [ 52 ] This study reported that the thermal activation of carbon substrates inhibits V(IV)/V(V) kinetics, but enhances the V(II)/V(III) reaction rate. The enhancement was attributed to the presence of COH groups on thermally treated carbon.…”

Section: All‐vanadium Rfbmentioning

confidence: 99%

Metal and Metal Oxide Electrocatalysts for Redox Flow Batteries

Amini

Gostick

Pritzker

2020

Adv Funct Materials

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Redox flow batteries (RFBs) are one of the promising technologies for large‐scale energy storage applications. For practical implementation of RFBs, it is of great interest to improve their efficiency and reduce their cost. One of the key components of RFBs that can greatly influence the efficiency and final cost is the electrode. The chemical and structural nature of electrodes can modify the kinetics of redox reactions and the accessibility of the electroactive species to available active sites. The ideal electrocatalyst for RFBs must have good activity for the desirable redox reaction, provide a high surface area, and exhibit sufficient conductivity and durability over repeated use. One strategy is to coat the electrode with metal and metal oxide electrocatalysts. Metal electrocatalysts have the advantage of high conductivity, while metal oxide catalysts are usually less expensive and so more economically attractive. In order to gain a better understanding of the performance of the electrocatalysts in RFBs, a comprehensive review of the progress in the development of metal and metal oxide electrocatalysts for RFBs is provided and a critical comparison of the latest developments is presented. Finally, practical recommendations for advancement of electrocatalysts and effective transfer of knowledge in this field are provided.

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“…[9][10][11][12] A lot of scientific and industrial activities regarding VFBs focus on improving graphite-based felt electrodes by the application of OFGs through oxidative treatments such as thermal, chemical, electrochemical, alkaline or acid activation, to facilitate the negative (V III + e − ⇌ V II , E 0 = −0.26 V vs. SHE) and positive (V V O2 + + 2 H + + e − ⇌ V IV O 2+ + H2O, E 0 = 1.0 V vs. SHE) half-cell reactions. [13][14][15][16][17][18][19][20][21] The later observed performance enhancement is then ascribed to an elevated quantity of surface oxygen. 5,22 However, there are contradictory results about the specific OFG (hydroxyl, carbonyl, or carboxylic group), which is suspected to be responsible for the increased activity.…”

Section: Introductionmentioning

confidence: 98%

Origin of the catalytic activity at graphite electrodes in vanadium flow batteries

Radinger

Ghamlouche

Ehrenberg

et al. 2021

Preprint

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For many electrochemical devices that use carbon-based materials such as electrolyzer, supercapacitors, and batteries, oxygen functional groups (OFGs) are considered essential to facilitate electron transfer. Researchers implement surface-active OFGs to improve the electrocatalytic properties of graphite felt electrodes in vanadium flow batteries. Herein, we show that graphitic defects and not OFGs are responsible for lowering the activation energy barrier and thus enhance the charge transfer properties. This is proven by a thermal deoxygenation procedure, in which specific OFGs are removed before electrochemical cycling. The electronic and microstructural changes associated with deoxygenation are studied by quasi in situ X-ray photoelectron and Raman spectroscopy. The removal of oxygen groups at basal and edge planes improves the activity by introducing new active edge sites and carbon vacancies. OFGs hinder the charge transfer at the graphite‒electrolyte interface. This is further proven by modifying the sp2 plane of graphite felt electrodes with oxygen-containing pyrene derivatives. The electrochemical evolution of OFGs and graphitic defects are studied during polarization and long-term cycling conditions. The hypothesis of increased activity caused by OFGs was refuted and hydrogenated graphitic edge sites were identified as the true reason for this increase.

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Impact of Surface Carbonyl- and Hydroxyl-Group Concentrations on Electrode Kinetics in an All-Vanadium Redox Flow Battery

Cited by 60 publications

References 65 publications

Influence and Electrochemical Stability of Oxygen Groups and Edge Sites in Vanadium Redox Reactions

Influence and Electrochemical Stability of Oxygen Groups and Edge Sites in Vanadium Redox Reactions

Metal and Metal Oxide Electrocatalysts for Redox Flow Batteries

Origin of the catalytic activity at graphite electrodes in vanadium flow batteries

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