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      Characteristics of Graphite Felt Electrodes Treated by Atmospheric Pressure Plasma Jets for an All-Vanadium Redox Flow Battery

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          Abstract

          In an all-vanadium redox flow battery (VRFB), redox reaction occurs on the fiber surface of the graphite felts. Therefore, the VRFB performance highly depends on the characteristics of the graphite felts. Although atmospheric pressure plasma jets (APPJs) have been applied for surface modification of graphite felt electrode in VRFBs for the enhancement of electrochemical reactivity, the influence of APPJ plasma reactivity and working temperature (by changing the flow rate) on the VRFB performance is still unknown. In this work, the performance of the graphite felts with different APPJ plasma reactivity and working temperatures, changed by varying the flow rates (the conditions are denoted as APPJ temperatures hereafter), was analyzed and compared with those treated with sulfuric acid. X-ray photoelectron spectroscopy (XPS) indicated that the APPJ treatment led to an increase in O-/N-containing functional groups on the GF surface to ~21.0% as compared to ~15.0% for untreated GF and 18.0% for H 2SO 4-treated GF. Scanning electron microscopy (SEM) indicated that the surface morphology of graphite felt electrodes was still smooth, and no visible changes were detected after oxidation in the sulfuric acid or after APPJ treatment. The polarization measurements indicated that the APPJ treatment increased the limiting current densities from 0.56 A·cm −2 for the GFs treated by H 2SO 4 to 0.64, 0.68, and 0.64 A·cm −2, respectively, for the GFs APPJ-treated at 450, 550, and 650 °C, as well as reduced the activation overpotential when compared with the H 2SO 4-treated electrode. The electrochemical charge/discharge measurements showed that the APPJ treatment temperature of 550 °C gave the highest energy efficiency of 83.5% as compared to 72.0% with the H 2SO 4 treatment.

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          Electrochemical energy storage for green grid.

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            A technology review of electrodes and reaction mechanisms in vanadium redox flow batteries

            The vanadium redox flow battery, which was first suggested by Skyllas-Kazacos and co-workers in 1985, is an electrochemical storage system which allows energy to be stored in two solutions containing different redox couples. The vanadium redox flow battery, which was first suggested by Skyllas-Kazacos and co-workers in 1985, is an electrochemical storage system which allows energy to be stored in two solutions containing different redox couples. Unlike commercially available batteries, all vanadium redox flow batteries have unique configurations, determined by the size of the electrolyte tanks. This technology has been proven to be an economically attractive and low-maintenance solution, with significant benefits over the other types of batteries. Moreover, the soaring demand for large-scale energy storage has, in turn, increased demands for unlimited capacity, design flexibility, and good safety systems. This work reviews and discusses the progress on electrodes and their reaction mechanisms as key components of the vanadium redox flow battery over the past 30 years. In terms of future outlook, we also provide practical guidelines for the further development of self-sustaining electrodes for vanadium redox flow batteries as an attractive energy storage system.
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              Chemical modification of graphite electrode materials for vanadium redox flow battery application—part II. Acid treatments

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                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                Materials (Basel)
                Materials (Basel)
                materials
                Materials
                MDPI
                1996-1944
                09 July 2021
                July 2021
                : 14
                : 14
                : 3847
                Affiliations
                [1 ]Center of Excellence in Process and Energy Systems Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand; tossaporn.jira@ 123456gmail.com (T.J.); justdao1994@ 123456gmail.com (A.C.)
                [2 ]Department of Mechanical Engineering and Advanced Institute of Manufacturing with High-Tech Innovations, National Chung Cheng University, Chiayi County 62102, Taiwan; bhup.bhu@ 123456gmail.com
                [3 ]Graduate Institute of Applied Mechanics, National Taiwan University, Taipei 10617, Taiwan; R08543006@ 123456ntu.edu.tw (J.-H.C.); jchen@ 123456ntu.edu.tw (J.-Z.C.)
                Author notes
                [* ]Correspondence: amornchai.a@ 123456chula.ac.th (A.A.); imeysc@ 123456ccu.edu.tw (Y.-S.C.)
                Author information
                https://orcid.org/0000-0002-0773-5312
                https://orcid.org/0000-0002-1071-2234
                https://orcid.org/0000-0001-9259-5010
                https://orcid.org/0000-0002-6182-6418
                Article
                materials-14-03847
                10.3390/ma14143847
                8304689
                34300767
                97d420ec-441e-4f8f-8d23-d4943601d68b
                © 2021 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( https://creativecommons.org/licenses/by/4.0/).

                History
                : 11 June 2021
                : 07 July 2021
                Categories
                Article

                all-vanadium redox flow battery,graphite felt,atmospheric pressure plasma jets,limiting current density,overpotential

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