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Research Papers

Activated Charcoal Modified Graphite Felts Using for Positive Electrodes of Vanadium Redox Flow Battery

[+] Author and Article Information
Haitao Yang

State Key Laboratory of Multiphase
Complex Systems,
Institute of Process Engineering,
Chinese Academy of Sciences,
Beijing 100190, China

Chuanlin Fan

State Key Laboratory of Multiphase
Complex Systems,
Institute of Process Engineering,
Chinese Academy of Sciences,
Beijing 100190, China
e-mail: chlfan@ipe.ac.cn

Qingshan Zhu

State Key Laboratory of Multiphase
Complex Systems,
Institute of Process Engineering,
Chinese Academy of Sciences,
Beijing 100190, China;
University of Chinese Academy of Sciences,
Beijing 100049, China
e-mail: qszhu@ipe.ac.cn

1Corresponding authors.

Manuscript received May 31, 2017; final manuscript received July 31, 2017; published online August 29, 2017. Assoc. Editor: Dirk Henkensmeier.

J. Electrochem. En. Conv. Stor. 14(4), 041004 (Aug 29, 2017) (6 pages) Paper No: JEECS-17-1061; doi: 10.1115/1.4037532 History: Received May 31, 2017; Revised July 31, 2017

In the present paper, a composite electrode material was developed for vanadium redox flow batteries (VRFBs). Activated charcoal particles were evenly immobilized on the graphite felt (GF) via a sucrose pyrolysis process for the first time. The in site formed pyrolytic carbon is used as the binder, because it is essentially carbon material as well as GF and activated charcoal, which has a natural tendency to realize good adhesion and low contact resistance. The activated charcoal decorated GF electrode (abbreviated as the composite electrode) possesses larger surface area (13.8 m2 g−1), more than two times as GF (6.3 m2 g−1). The oxygen content of composite electrode is also higher (7.0%) than that of GF (4.8%). The composite electrode was demonstrated to lower polarization and increase the reversibility toward the VO2+/VO2+ redox couple according to the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The charge–discharge cycling test was conducted with a single VRFB cell. The results indicate that the cell with composite electrode presents higher charge–discharge capacity, larger electrolyte utilization efficiency (EU), and higher energy conversion efficiency (79.1%) compared with that using GF electrode. The increasing electrochemical performances of composite electrodes are mainly ascribed to the high electrochemical activity of activated charcoal particles and increasing superficial area.

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Figures

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Fig. 1

Scanning electron microscope and X-ray photoelectron spectroscopy (XPS) of experimental specimens: (a) SEM of the graphite felt before charging–discharging cycle, (b) SEM of the composite electrode before charging–discharging cycle, (c) SEM of the composite electrode after 15 charging–discharging cycles, and (d) XPS spectra of the GF and composite electrode before charging–discharging cycle

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Fig. 2

Cyclic voltammograms of the GF and composite electrode sample in 0.1 M VOSO4 + 2.0 M H2SO4 solutions at a scan rate of 2 mV·s−1 from 0 V to 1.6 V

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Fig. 3

EIS patterns (scatters: experimental and lines: simulated) of the GF and composite electrode in 0.1 M VOSO4 + 2.0 M H2SO4 solutions at the potential 1.05 V by applying an AC voltage of 5 mV amplitude in the frequency range from 105 to 10−2 Hz

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Fig. 4

Electrical equivalent circuit used to simulate the impedance data

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Fig. 5

Charge–discharge voltage profiles for VRFBs employed GF and composite electrode at the current density of 100 mA/cm2

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Fig. 6

Discharge capacity curves for VRFBs employing the graphite felt and composite electrode at the current density of 100 mA/cm2 during the first 15 cycles

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Fig. 7

The cycling performances of VRFBs with the graphite felt and composite electrode at the current density of 100 mA cm−2 from 0.8 V to 1.8 V

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