vanadium redox flow batteries hierarchical electronic and ... · The cyclic voltammetry (CV) measurements performed on the electrochemical workstation (CHI760D) were applied to analyze
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Electronic Supplementary Information (ESI)
Phosphorus and oxygen co-doped composite electrode with
hierarchical electronic and ionic mixed conducting networks for
[email protected] Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy
of Sciences (CAS), Beijing 100190, China. E-mail: [email protected]. School of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, China.d.Automotive & Transportation Engineering, Shenzhen Polytechnic, Shenzhen, Guangdong 518055, China;
‡The authors equally contributed to this work.
ExperimentPreparation of the GF-TCNs electrode The GO solution was fabricated for standby application according to Hummers’ method.1 Firstly, 1.2 mL phytic acid solution (70 %) was added to 45 mL GO solution (2 mg mL-1) under intensive mixing, and the GFs (3 cm × 4 cm) were immersed in the aboved solution with 30 min ultrasonic dispersion. Next, the mixed compounds were sealed in an 80 mL Teflon-lined autoclave and underwent a hydrothermal reaction at 180 °C for 12 h. After vacuum freeze drying for 24 h, the resulting products were annealed in a quartz tube furnace under the argon atmosphere at 800 °C for 1 h. Finally, the obtained GFs and black solid were washed three times with deionized water and dried to constant weight at 80 °C for 10 h, and labeled GF-TCNs and TCNs, respectively.
For comparison purposes, the treated GFs named GF-rGO were prepared by an identical process as the GF-TCNs without the addition of phytic acid, and the residual black solid labeled rGO.Structural characterizationThe morphologies and element distribution of the electrode materials were characterized from scanning electron microscope (SEM, JSM-6701F) operated at 10 kV with energy dispersive spectrometer (EDS). The structural properties of the electrode materials were analyzed by X-ray diffraction spectra (XRD, D/max 2500), and Raman spectra (Lab RAM HR Evolution) with a 532 nm laser excitation. The element compositions of the samples were determined by X-ray photoelectron spectroscopy (XPS, ESCALAB250XI) based on a Thermo Scientific ESCALab 250Xi with 200 W Al Kα radiation. The electrolyte wettability of electrodes was tested using 100 μL electrolytes (0.1 mol L-1 (M) VOSO4 in 3 M H2SO4) drop on the surface of electrodes.Electrochemical tests
The cyclic voltammetry (CV) measurements performed on the electrochemical workstation (CHI760D) were applied to analyze the electrode reaction process via a three-electrode system2 in the 0.1 M VOSO4 + 3 M H2SO4 electrolyte, and the working electrode area is 0.5 cm× 0.5 cm. The impedance experiments (EIS) are conducted with a frequency range of 0.01-100 kHz at an amplitude of 5 mV under the same test condition as CV, and the data were fitted based on equivalent circuit diagram. The VRFBs assembled pristine GFs and GF-TCNs electrodes (2 × 2 cm2) were performed for the galvanostatic charging and discharging tests with Nafion 115 (DuPont, USA) as the separator, and the electrolyte was 0.75 M VOSO4 + 0.375 M V2(SO4)3 + 3 M H2SO4 (15 mL) (Hunan Yinfeng Co. Ltd.). The voltage windows of the dischargeand charge measurements were set as 1.60–0.95 V, 1.65–0.85 V, 1.65-0.80 V and 1.70-0.80 V at current densities range of 100-150 mA cm-2, 200-225 mA cm-2, 250-300 mA cm-2 and 350 mA cm-2, respectively.