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Mass production of highly-porous graphene for high-performance supercapacitors

View Article: PubMed Central - PubMed

ABSTRACT

This study reports on a facile and economical method for the scalable synthesis of few-layered graphene sheets by the microwave-assisted functionalization. Herein, single-layered and few-layered graphene sheets were produced by dispersion and exfoliation of functionalized graphite in ethylene glycol. Thermal treatment was used to prepare pure graphene without functional groups, and the pure graphene was labeled as thermally-treated graphene (T-GR). The morphological and statistical studies about the distribution of the number of layers showed that more than 90% of the flakes of T-GR had less than two layers and about 84% of T-GR were single-layered. The microwave-assisted exfoliation approach presents us with a possibility for a mass production of graphene at low cost and great potentials in energy storage applications of graphene-based materials. Owing to unique surface chemistry, the T-GR demonstrates an excellent energy storage performance, and the electrochemical capacitance is much higher than that of the other carbon-based nanostructures. The nanoscopic porous morphology of the T-GR-based electrodes made a significant contribution in increasing the BET surface as well as the specific capacitance of graphene. T-GR, with a capacitance of 354.1 Fg−1 at 5 mVs−1 and 264 Fg−1 at 100 mVs−1, exhibits excellent performance as a supercapacitor.

No MeSH data available.


(a) FTIR spectra of pristine graphite, CE-GR and T-GR, TGA (black) and DTG (orange) curves of (b) pristine graphite, (c) CE-GR, (d) T-GR and (e) Raman spectra of pristine graphite, CE-GR and T-GR.
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f1: (a) FTIR spectra of pristine graphite, CE-GR and T-GR, TGA (black) and DTG (orange) curves of (b) pristine graphite, (c) CE-GR, (d) T-GR and (e) Raman spectra of pristine graphite, CE-GR and T-GR.

Mentions: Figure 1(a) shows the FTIR spectra of pristine graphite, CE-GR, and T-GR. It is seen that the FTIR spectrum of pristine graphite provided no evidence of PEG. The peaks at 1471, 1535 and 1577 cm−1 were respectively consistent with the bending vibration of the CH2 group, stretching vibrations of the C=C and C=O. In contrast, the FTIR spectrum of CE-GR had two peaks in the range of 2800–3000 cm−1, which were associated with the C-H stretching vibration31. The peak at 1548 cm−1 was consistent with C=O or C=C stretching vibrations, which are infrared-activated by extensive functionalization. Also, the OH stretching vibration produced a weak peak at 3455 cm−1, indicating the presence of hydroxyl groups attached to the graphite. The FTIR spectrum of the treated samples also had a peak at 1460 cm−1, representing the bending vibration of the CH2 group. The peak at 1182 cm−1 was in agreement with the stretching vibration of the C–O groups. In contrast to the CE-GR, T-GR showed no evidence of PEG molecules, which confirmed that all of the functional groups had been removed. The FTIR spectrum of T-GR shows two weak peaks in the range of 2800–3000 cm−1, which were associated with the C-H stretching vibration. The lack of above-mentioned peaks in T-GR spectrum shows the prepared graphene was almost pure and that a majority of the functional groups had been removed32333435. To provide evidence supporting the above statements, thermogravimetric analysis (TGA) was used to detect quantitatively the weight fraction (loading) of organic groups attached to the graphite. Figure 1b–d (black curves) show the TGA curves of the pristine graphite, CE-GR, and T-GR samples, respectively. Also, Fig. 1b–d show the differential thermogravimetric analysis (DTG) curves (orange curves) of the pristine graphite, CE-GR, and T-GR powders after filtration. It is apparent that there was no significant weight loss with pristine graphite, which was thermally stable when heated to 770 °C under an air flow rate of 50 cm3/min. The DTG curves also show that there were two phases of degradation with the CE-GR sample. CE-GR illustrates a mild weight loss in the temperature range of 100–205 °C, which was due to the decomposition of the covalently-grafted organic addends (PEG). To address this issue, the TGA and DTG curves of pure PEG are also shown in Figure S5. It can be seen that the main weight loss occurred over the temperature range of 110–200 °C, which is in agreement with our claim.


Mass production of highly-porous graphene for high-performance supercapacitors
(a) FTIR spectra of pristine graphite, CE-GR and T-GR, TGA (black) and DTG (orange) curves of (b) pristine graphite, (c) CE-GR, (d) T-GR and (e) Raman spectra of pristine graphite, CE-GR and T-GR.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015014&req=5

f1: (a) FTIR spectra of pristine graphite, CE-GR and T-GR, TGA (black) and DTG (orange) curves of (b) pristine graphite, (c) CE-GR, (d) T-GR and (e) Raman spectra of pristine graphite, CE-GR and T-GR.
Mentions: Figure 1(a) shows the FTIR spectra of pristine graphite, CE-GR, and T-GR. It is seen that the FTIR spectrum of pristine graphite provided no evidence of PEG. The peaks at 1471, 1535 and 1577 cm−1 were respectively consistent with the bending vibration of the CH2 group, stretching vibrations of the C=C and C=O. In contrast, the FTIR spectrum of CE-GR had two peaks in the range of 2800–3000 cm−1, which were associated with the C-H stretching vibration31. The peak at 1548 cm−1 was consistent with C=O or C=C stretching vibrations, which are infrared-activated by extensive functionalization. Also, the OH stretching vibration produced a weak peak at 3455 cm−1, indicating the presence of hydroxyl groups attached to the graphite. The FTIR spectrum of the treated samples also had a peak at 1460 cm−1, representing the bending vibration of the CH2 group. The peak at 1182 cm−1 was in agreement with the stretching vibration of the C–O groups. In contrast to the CE-GR, T-GR showed no evidence of PEG molecules, which confirmed that all of the functional groups had been removed. The FTIR spectrum of T-GR shows two weak peaks in the range of 2800–3000 cm−1, which were associated with the C-H stretching vibration. The lack of above-mentioned peaks in T-GR spectrum shows the prepared graphene was almost pure and that a majority of the functional groups had been removed32333435. To provide evidence supporting the above statements, thermogravimetric analysis (TGA) was used to detect quantitatively the weight fraction (loading) of organic groups attached to the graphite. Figure 1b–d (black curves) show the TGA curves of the pristine graphite, CE-GR, and T-GR samples, respectively. Also, Fig. 1b–d show the differential thermogravimetric analysis (DTG) curves (orange curves) of the pristine graphite, CE-GR, and T-GR powders after filtration. It is apparent that there was no significant weight loss with pristine graphite, which was thermally stable when heated to 770 °C under an air flow rate of 50 cm3/min. The DTG curves also show that there were two phases of degradation with the CE-GR sample. CE-GR illustrates a mild weight loss in the temperature range of 100–205 °C, which was due to the decomposition of the covalently-grafted organic addends (PEG). To address this issue, the TGA and DTG curves of pure PEG are also shown in Figure S5. It can be seen that the main weight loss occurred over the temperature range of 110–200 °C, which is in agreement with our claim.

View Article: PubMed Central - PubMed

ABSTRACT

This study reports on a facile and economical method for the scalable synthesis of few-layered graphene sheets by the microwave-assisted functionalization. Herein, single-layered and few-layered graphene sheets were produced by dispersion and exfoliation of functionalized graphite in ethylene glycol. Thermal treatment was used to prepare pure graphene without functional groups, and the pure graphene was labeled as thermally-treated graphene (T-GR). The morphological and statistical studies about the distribution of the number of layers showed that more than 90% of the flakes of T-GR had less than two layers and about 84% of T-GR were single-layered. The microwave-assisted exfoliation approach presents us with a possibility for a mass production of graphene at low cost and great potentials in energy storage applications of graphene-based materials. Owing to unique surface chemistry, the T-GR demonstrates an excellent energy storage performance, and the electrochemical capacitance is much higher than that of the other carbon-based nanostructures. The nanoscopic porous morphology of the T-GR-based electrodes made a significant contribution in increasing the BET surface as well as the specific capacitance of graphene. T-GR, with a capacitance of 354.1 Fg−1 at 5 mVs−1 and 264 Fg−1 at 100 mVs−1, exhibits excellent performance as a supercapacitor.

No MeSH data available.