Step-by-Step Modification of Graphite Felt Electrode for Vanadium Redox Flow Battery

Authors

Jing-yuan LOU, School of Environmental and Material Engineering, Yantai University, Yantai 264000, Shandong, China;
Dong-jiang YOU, School of Environmental and Material Engineering, Yantai University, Yantai 264000, Shandong, China;Follow
Xue-jing LI, School of Environmental and Material Engineering, Yantai University, Yantai 264000, Shandong, China;

Corresponding Author

Dong-jiang YOU(youdj718@163.com)

Abstract

As a well-known electrode material of the vanadium redox flow battery (VRFB),graphite felt electrode is the frequently-used electrode material in VRFB, and its low electrochemical activity is one of the key factors for the low power density of VRFB. In this work, we proposed a step-by-step modification method, which used KMnO₄ to oxidize graphite felt first and then placed in an activation solution to excite its reactivity, to improve the electrochemical performance of the graphite felt electrode. According to the results from cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) characterizations of the treated graphite felts, it was found that the oxidation time and the composition of the activation solution are factors affecting the electrode performance. In this paper, the charge transfer resistance of the electrode treated in the activation solution with a volume ratio of H₂SO₄:H₂O₂ = 3:1 after oxidation in KMnO₄ for 3 days, was significantly lower than that of the electrode treated by other methods, showing the lowest contact resistance (7.33 Ω·cm ²). The redox peak current density ratio (I_pa /I_pc) was closer to 1, which effectively increased the activity and reversibility of the redox reactions. In addition, the XPS data showed that the excellent electrochemical performance of the treated graphite felt might be related to the increase in the number of surface oxygen-containing functional groups. The charge/discharge testing results demonstrated that the all-vanadium redox flow battery employing the modified graphite felt electrodes exhibited the enhanced performance with higher battery efficiency and favorable discharge capacity. Moreover, the all-vanadium redox flow battery with the treated graphite felt as an electrode delivered the energy efficiency of 7.47%, which was higher than that of the untreated electrode at a current density at 100 mA·cm ^-2. Compared with heat treatment, acid treatment and electrochemical oxidation, the step-by-step modification method requires no auxiliary equipment and consumes no energy.

Graphical Abstract

Keywords

vanadium redox flow battery, graphite felt, step-by-step modification, activity

DOI Link

https://doi.org/10.13208/j.electrochem.190714

Publication Date

2020-12-28

Online Available Date

2020-02-12

Revised Date

2019-10-05

Received Date

2019-07-14

Recommended Citation

Jing-yuan LOU, Dong-jiang YOU, Xue-jing LI. Step-by-Step Modification of Graphite Felt Electrode for Vanadium Redox Flow Battery[J]. Journal of Electrochemistry, 2020 , 26(6): 876-884.
DOI: 10.13208/j.electrochem.190714
Available at: https://jelectrochem.xmu.edu.cn/journal/vol26/iss6/14