研究目的
To improve the thermoelectric properties of reduced graphene oxide (rGO) and its composites by using vanadium salt-assisted solvothermal reduction.
研究成果
The vanadium salt-assisted solvothermal reduction significantly improves the electrical conductivity and thermoelectric properties of rGO. SBS composites with the modified rGO show enhanced conductivity and flexibility, with a maximum power factor of 4.6 x 10-4 μW/(m·K2), but values are still lower than other materials. The approach widens potential applications due to flexibility.
研究不足
The power factors achieved are lower than those of many other thermoelectric materials. The method may lead to vanadium by-product formation at high VCl3 concentrations, and the composites exhibit sedimentation of fillers during processing.
1：Experimental Design and Method Selection:
The study employed a solvothermal method for reducing graphene oxide (GO) with the addition of vanadium chloride (VCl3) to enhance reduction efficiency. The rationale was to increase electrical conductivity and thermoelectric performance. Theoretical models included the use of Tauc's plot for bandgap calculation and XPS for elemental analysis.
2：Sample Selection and Data Sources:
GO was synthesized from graphite flakes using the modified Hummers method. Reduction was performed with varying concentrations of VCl3 and ammonium hydroxide. Composites were prepared with SBS copolymer and rGO fillers.
3：List of Experimental Equipment and Materials:
Equipment included ultrasonic baths, autoclaves, SEM, Raman spectrometer, UV-vis spectrometer, XRD, XPS, and electrical conductivity/Seebeck coefficient measurement setups. Materials included graphite, chemicals for GO synthesis, VCl3, NH4OH, methanol, THF, and SBS copolymer.
4：Experimental Procedures and Operational Workflow:
GO synthesis involved oxidation, washing, and freeze-drying. Reduction was done by dispersing GO in methanol, adding VCl3 and NH4OH, probe sonication, and autoclave treatment at 180°C for 6 hours. Composites were made by solution mixing, casting, and drying.
5：Data Analysis Methods:
Data were analyzed using software for Raman spectra smoothing, XPS deconvolution, and calculation of electrical conductivity, Seebeck coefficient, and power factor from measured values.
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Graphite flakes
99% purity, median: 7-10 μm
Sigma-Aldrich
Starting material for graphene oxide synthesis
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Sodium nitrate
ACS reagent, ≥99%
Sigma-Aldrich
Chemical used in GO synthesis
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Sodium persulfate
reagent grade, ≥99%
Sigma-Aldrich
Chemical used in GO synthesis
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Potassium permanganate
ACS reagent, ≥99%
Sigma-Aldrich
Oxidizing agent in GO synthesis
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Hydrogen peroxide
30 wt% solution
Sigma-Aldrich
Used to destroy excess KMnO4 in GO synthesis
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Sulphuric acid
96%
Sigma-Aldrich
Acid used in GO synthesis
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HCl
reagent grade, 37%
Sigma-Aldrich
Used for washing in GO synthesis
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Ammonium hydroxide
28%
Sigma-Aldrich
Base used in reduction process
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Vanadium(III) chloride
97%
Sigma-Aldrich
Reductant in solvothermal reduction
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Tetrahydrofuran
ACS reagent, ≥99%
Sigma-Aldrich
Solvent for composite preparation
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Scanning electron microscope
NEON 40
Carl Zeiss AG
Morphology examination of nanoparticles and composites
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Raman Imaging Microscope System
alpha300R
WITec GmbH
Raman spectroscopy for defect analysis
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UV-visible spectrometer
Cary 6000i
Agilent
UV-vis absorption spectra measurement
Cary 60 UV-Vis Spectrophotometer
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Styrene-butadiene-styrene triblock copolymer
KratonTM D1102 A, 28.5% styrene content
Kraton
Polymer matrix for composites
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Digital multimeter
Keithley 6517 A
Keithley Instruments
Electrical conductivity measurement for high resistivity samples
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Digital multimeter
Keithley 2001
Keithley Instruments
Electrical conductivity measurement for low resistivity samples and powders
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X-ray diffractometer
XRD 3003 T/T
GE Sensing & Inspection Technologies, Seifert-FPM
XRD analysis for structural characterization
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Photoelectron spectrometer
Axis Ultra
Kratos Analytical
XPS analysis for elemental composition
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Ultrasonic bath
Bandelin Sonorex Digitec
Bandelin
Sonication for dispersion
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Ultrasonic device
UP400S
Hielscher Ultrasonics GmbH
Probe sonication for dispersion
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