- Email: [email protected]
Superior capacitive performance of reduced graphene hydrogels via dimethyl ketoxime
Author’s Accepted Manuscript Superior capacitive performance of reduced graphene hydrogels via dimethyl ketoxime Ling-Bao Xing, Jing-Li Zhang, Kun Qin, TianZhen Liu, Jin Zhou, Weijiang Si, Shuping Zhuo www.elsevier.com
PII: DOI: Reference:
S0167-577X(16)30618-8 http://dx.doi.org/10.1016/j.matlet.2016.04.122 MLBLUE20719
To appear in: Materials Letters Received date: 16 October 2015 Revised date: 28 March 2016 Accepted date: 16 April 2016 Cite this article as: Ling-Bao Xing, Jing-Li Zhang, Kun Qin, Tian-Zhen Liu, Jin Zhou, Weijiang Si and Shuping Zhuo, Superior capacitive performance of reduced graphene hydrogels via dimethyl ketoxime, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.04.122 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Superior capacitive performance of reduced graphene hydrogels via dimethyl ketoxime Ling-Bao Xing, Jing-Li Zhang, Kun Qin, Tian-Zhen Liu, Jin Zhou, Weijiang Si, Shuping Zhuo* School of Chemical Engineering, Shandong University of Technology, Zibo 255049, P. R. China *Corresponding author. Tel. /fax: +86 533 2781664. [email protected]
Abstract
Three-dimensional (3D) reduced graphene hydrogels (RGHs) have been prepared by using dimethyl ketoxime as reducing agents in aqueous solution of graphene oxide (GO) with ammonia. The structure and surface chemistry were analyzed by scanning electron microscopy, Raman, X-ray diffraction, and X-ray photoelectron spectroscopy. The capacitive performance of the RGHs materials are studied in 6 M KOH electrolyte. Benefitting from the 3D porous structures and heteroatom-doped polar pore surface, the as-prepared RGHs materials exhibit high specific capacitances up to 159.8, 215.1 and 163.4 F g-1 at 1 A g-1 for RGHs-1, RGHs-2 and RGHs-5, respectively. More importantly, the materials can maintain high capacitances of 95.6, 155.2 and 118.9 F g-1 at a very high current density of 20 A g-1, the retention rates are 59.8, 72.2 and 72.8％ for RGHs-1, RGHs-2 and RGHs-5, respectively.
1
Keywords: carbon materials; porous materials; three-dimensional; dimethyl ketoxime; supercapacitor. 1. Introduction Because of its multiple appealing features, including high specific surface area, excellent electrical conductivity, and extraordinary chemical/electrochemical stability and mechanical flexibility, graphene has attracted considerable interest for the past few years. However, the strong van der Waals and π-π stacking interactions between graphene sheets make them easily aggregate to form graphite structure, leading to a great loss of specific surface area.[1-2] In order to fully utilize the high intrinsic surface area and further explore the new functions of graphene, self-assembly of nanoscale graphene into monolithic macroscopic materials with 3D porous networks can largely translate the properties of individual graphene into the resulting macrostructures.[1-12] The formation of 3D graphene network can effectively prevent graphene from restacking and retain the high specific surface area. Additionally, with a highly interconnected graphene network for excellent electron transport and interpenetrated porous network for rapid ion transport, the 3D graphene macrostructures are ideally suited for supercapacitor electrodes. In order to further investigate the preparation and application of 3D graphene structures, we demonstrate an efficient and facile strategy to fabricate reduced graphene hydrogels (RGHs) by using dimethyl ketoxime ((CH3)2C=NOH) as reducing agent, in which it can not only reduce GO by the generated hydroxylammonium under alkaline 2
condition through hydrolysis of dimethyl ketoxime [13], but also induce the reduced GO sheets to self-assembly into 3D hydrogels through van der Waals and π-π stacking interactions. Moreover, the RGHs obtained herein have several advantages including low reaction temperature (90 °C), short reaction time (1 h), and high performance (max. 215.1 F g-1) in supercapacitor compared to the reported work in other processes (table S1). The morphology, crystal structure, chemical bonding, elemental composition and porosity of the as-prepared RGHs have been studied. Benefiting from well-defined and cross-linked 3D porous network architectures, the supercapacitors based on the RGHs in KOH electrolyte exhibited a high specific capacitance and good electrochemical stability in the repetitive charge/discharge cycling test. 2. Experimental details 2.1 Materials. Graphite powder was purchased from Qingdao Huatai Lubricant Sealing S&T Co. Ltd. All other chemicals were purchased from Sinopharm Chemical Reagent Co. Ltd and used directly without further purification. 2.2 Preparation of RGHs and characterization. GO was synthesized from graphite powder (325 mesh) by a modified Hummers method, which possessed good dispersion in monolayered sheets as in our previous work [14]. The preparation process (Fig. S1) and characterization of RGHs can be found in the supplementary material. 3. Results and discussions
3
Fig. 1. The morphology of RGHs was characterized by field emission scanning electron microscopy (FESEM). As imaged by SEM images with different magnifications of freeze-dried samples, RGHs-1 (Fig. 1a-c), RGHs-2 (Fig. 1d-f) and RGHs-5 (Fig. 1g-i) showed typical 3D network and porous structures forming by wrinkling and folding of graphene sheets through π-π stacking and hydrophobic interactions. From the disappeared peak at 9.74° (6.94 Å) in GO and new broad bumps at 24.66, 23.77 and 24.34° which corresponding to interplanar spacing of 3.61, 3.74 and 3.65 Å for RGHs-1, RGHs-2 and RGHs-5 (Fig. 2a), it can be seen that the hydrogels have been formed. In order to confirm the reduction process, Raman spectra was carried out as shown in Fig. 2b. Two fundamental vibrations of D band at 1350 cm-1 and G band at 1597 cm-1 were clearly observed. The intensity ratio of ID/IG increased from 0.89 of GO to 0.97, 1.05 and 1.03 for RGHs-1, RGHs-2 and RGHs-5, indicating the removal of oxygenated groups. FT-IR spectra (Fig. 2c) showed that the broad band at 3000-3500 cm-1 related to hydroxyl groups (O-H) and peak at 1730 cm-1 related to carbonyl and carboxyl groups decreased dramatically in RGHs, further indicating the efficiently removal of the oxygen-contained groups. Moreover, the obvious increase of the peaks at
4
3128, 3039, 1549, 1398 and 1070 cm-1 attributed to stretching vibrations of C-H and C-C further illustrated the reduction of GO. A new peak at 1550 cm−1 corresponding to the N-H bending vibration appears, implying the doping of nitrogen in the reducing process. The element compositions of RGHs are determined by XPS measurement (Fig. 2d) and the content of different elements are listed in Table S2. Based on the XPS results, nitrogen doping of RGHs are confirmed, in which the N content of RGHs is in the range of 3.83-4.22 atm.%. Apparently, the decrease of O content and increase of C content in RGHs further confirm the reduction process.
Fig. 2. In order to investigate the atom binding states of the prepared materials, the high resolution XPS measurements were carried out as shown in Fig. 3, which showed the C1s, O1s and N1s deconvolution spectra of RGHs-1 (a, b, c), RGHs-2 (d, e, f) and RGHs-5 (h, i, j), respectively. In case of C1s of RGHs-1, four peaks at 284.8, 286.7, 287.0 and 288.8 eV corresponding to C=C/C-C in sp2-hybridized domains, C-O (epoxy and hydroxyl), C=O (carbonyl) and O=C-O (carboxyl) groups were observed. Besides, the appearance of the new characteristic peak corresponding to C-N bond (285.7 eV) indicates the successful doping of nitrogen. The N1s of RGHs-1 are determined by 5
398.7, 400.2 and 401.6 eV, which can be attributed to pyridinic N, pyrrolic N and graphitic N, respectively. In case of O1s of RGHs-1, three peaks of C-O (epoxy and hydroxyl), C=O (carbonyl), and O=C-O (carboxyl) groups are determined by the peaks at 531.8, 532.7 and 533.6 eV, respectively. All the high-resolution XPS spectra demonstrate the effective removal of oxygen-containing groups and doping of nitrogen by dimethyl ketoxime with ammonia in the reduction process.
Fig. 3. The electrochemical properties of the supercapacitor electrodes based on RGHs are investigated through cyclic voltammograms (CV). As shown in Fig. 4a-c and Fig. S2a, obvious current enlargement spread over a wide range of -0.4~-0.9 V on the CV curves of RGHs could be observed, indicating the existence of large pseudo-capacitance. The capacitive behavior was further tested by a galvanostatic charge/discharge experiment at different current density. From the discharge curve, the specific capacitance of the RGHs electrodes are evaluated to be 159.8, 215.1 and 163.4 F g−1 at 1 A g-1 for RGHs-1, RGHs-2 and RGHs-5, respectively (Fig. S2b). The specific capacitances of RGHs are further investigated with the increasing of charge/discharge current density. It can be seen that the specific capacitances decrease at high charging/discharging current density. 6
However, RGHs can still be maintained specific capacitances of 95.6, 155.2 and 118.9 F g-1 at a very high current density of 20 A g-1, the retention rates are 59.8, 72.2 and 72.8％ for RGHs-1, RGHs-2 and RGHs-5, respectively (Fig. 4d-f and Fig. S3a).
Fig. 4. Nyquist plots of RGHs in a frequency range from 10 mHz to 100 kHz were measured (Fig. S3b), which are composed of three distinct parts at different frequency range, including an uncompleted semicircle part at high frequency, an inclined portion of the curve (about 45°) at middle frequency and a linear part at low frequency. At very high frequencies, the imaginary impedance is near to zero and the corresponding real impedance (Z’) is the sum of ohmic resistances derived from the electrolyte and the contact between the electrode and the current collector. The 45° slope region at middle frequency can be attributed to the ions diffusion/transport from the electrolyte to the pore on the surface. The almost vertical line represents the dominance of ideal double-layer charge/discharge behaviors at low frequency. 4. Conclusions In summary, 3D reduced graphene hydrogels are prepared through an efficient and facile way by using dimethyl ketoxime as reducing and doping agents. Benefiting from 7
well-defined and cross-linked 3D porous network architectures, the supercapacitors based on the RGHs exhibited a high specific capacitance and good electrochemical stability in the repetitive charge/discharge cycling test, which indicating the good rate performance of the investigated RGHs ascribed to its porous structures and heteroatom-doped species. Acknowledgements We are grateful for the financial support from the National Natural Science Foundation of China (21402108), Shandong Natural Science Foundation (ZR2014BQ036) and Young Teacher Supporting Fund of Shandong University of Technology. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version. References
[1] Xu Y, Sheng K, Li C, Shi G. ACS Nano 2010;4:4324-30.
[2] Xu Y, Shi G, Duan X. Acc Chem Res 2015;48:1666-75.
[3] Li C, Shi G. Adv Mater 2014;26:3992-4012.
[4] Nardecchia S, Carriazo D, Ferrer ML, Gutierrez MC, del Monte F. Chem Soc Rev 2013;42:794-830.
[5] Cong H-P, Chen J-F, Yu S-H. Chem Soc Rev 2014;43:7295-325.
8
[6] Xu Y, Shi G. J Mater Chem 2011;21:3311-23.
[7] Jiang L, Fan Z. Nanoscale 2014;6:1922-45.
[8] Li C, Shi G. Nanoscale 2012;4:5549-63.
[9] Zhang X, Zhang H, Li C, Wang K, Sun X, Ma Y. RSC Adv 2014;4:45862-84.
[10] Luo B, Zhi L. Energy Environ Sci 2015;8:456-77.
[11] Wu X-L, Xu A-W. J Mater Chem A 2014;2:4852-64.
[12] Xia XH, Chao DL, Zhang YQ, Shen ZX, Fan HJ. Nano Today 2014;9:785-807.
[13] Su P, Guo H-L, Tian L, Ning S-K. Carbon 2012;50:5351-8.
[14] Xing L-B, Hou S-F, Zhou J, Li S, Zhu T, Li Z, et al. J Phys Chem C 2014;118:25924-30.
Figure Captions
Fig. 1. FESEM images of RGHs with different magnifications.
Fig. 2. XRD (a), Raman (b), FT-IR (c) spectra and XPS survey of GO and RGHs.
Fig. 3. High-resolution XPS spectra of C1s, O1s and N 1s of RGHs-1 (a-c), RGHs-2 (d-f) and RGHs-5 (g-i).
9
Fig. 4. Cyclic voltammograms of the supercapacitors based on RGHs at different scan rates (a-c); galvanostatic charge/discharge curves of RGHs at different charging/discharging current density (d-f).
10
Highlights
Three-dimensional reduced graphene hydrogels (RGHs) were prepared.
Dimethyl ketoxime was used as reducing and doping agents.
SEM showed typical three-dimensional network and porous structures.
RGHs electrodes exhibited a high specific capacitance in supercapacitors.
11
PII: DOI: Reference:
S0167-577X(16)30618-8 http://dx.doi.org/10.1016/j.matlet.2016.04.122 MLBLUE20719
To appear in: Materials Letters Received date: 16 October 2015 Revised date: 28 March 2016 Accepted date: 16 April 2016 Cite this article as: Ling-Bao Xing, Jing-Li Zhang, Kun Qin, Tian-Zhen Liu, Jin Zhou, Weijiang Si and Shuping Zhuo, Superior capacitive performance of reduced graphene hydrogels via dimethyl ketoxime, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.04.122 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Superior capacitive performance of reduced graphene hydrogels via dimethyl ketoxime Ling-Bao Xing, Jing-Li Zhang, Kun Qin, Tian-Zhen Liu, Jin Zhou, Weijiang Si, Shuping Zhuo* School of Chemical Engineering, Shandong University of Technology, Zibo 255049, P. R. China *Corresponding author. Tel. /fax: +86 533 2781664. [email protected]
Abstract
Three-dimensional (3D) reduced graphene hydrogels (RGHs) have been prepared by using dimethyl ketoxime as reducing agents in aqueous solution of graphene oxide (GO) with ammonia. The structure and surface chemistry were analyzed by scanning electron microscopy, Raman, X-ray diffraction, and X-ray photoelectron spectroscopy. The capacitive performance of the RGHs materials are studied in 6 M KOH electrolyte. Benefitting from the 3D porous structures and heteroatom-doped polar pore surface, the as-prepared RGHs materials exhibit high specific capacitances up to 159.8, 215.1 and 163.4 F g-1 at 1 A g-1 for RGHs-1, RGHs-2 and RGHs-5, respectively. More importantly, the materials can maintain high capacitances of 95.6, 155.2 and 118.9 F g-1 at a very high current density of 20 A g-1, the retention rates are 59.8, 72.2 and 72.8％ for RGHs-1, RGHs-2 and RGHs-5, respectively.
1
Keywords: carbon materials; porous materials; three-dimensional; dimethyl ketoxime; supercapacitor. 1. Introduction Because of its multiple appealing features, including high specific surface area, excellent electrical conductivity, and extraordinary chemical/electrochemical stability and mechanical flexibility, graphene has attracted considerable interest for the past few years. However, the strong van der Waals and π-π stacking interactions between graphene sheets make them easily aggregate to form graphite structure, leading to a great loss of specific surface area.[1-2] In order to fully utilize the high intrinsic surface area and further explore the new functions of graphene, self-assembly of nanoscale graphene into monolithic macroscopic materials with 3D porous networks can largely translate the properties of individual graphene into the resulting macrostructures.[1-12] The formation of 3D graphene network can effectively prevent graphene from restacking and retain the high specific surface area. Additionally, with a highly interconnected graphene network for excellent electron transport and interpenetrated porous network for rapid ion transport, the 3D graphene macrostructures are ideally suited for supercapacitor electrodes. In order to further investigate the preparation and application of 3D graphene structures, we demonstrate an efficient and facile strategy to fabricate reduced graphene hydrogels (RGHs) by using dimethyl ketoxime ((CH3)2C=NOH) as reducing agent, in which it can not only reduce GO by the generated hydroxylammonium under alkaline 2
condition through hydrolysis of dimethyl ketoxime [13], but also induce the reduced GO sheets to self-assembly into 3D hydrogels through van der Waals and π-π stacking interactions. Moreover, the RGHs obtained herein have several advantages including low reaction temperature (90 °C), short reaction time (1 h), and high performance (max. 215.1 F g-1) in supercapacitor compared to the reported work in other processes (table S1). The morphology, crystal structure, chemical bonding, elemental composition and porosity of the as-prepared RGHs have been studied. Benefiting from well-defined and cross-linked 3D porous network architectures, the supercapacitors based on the RGHs in KOH electrolyte exhibited a high specific capacitance and good electrochemical stability in the repetitive charge/discharge cycling test. 2. Experimental details 2.1 Materials. Graphite powder was purchased from Qingdao Huatai Lubricant Sealing S&T Co. Ltd. All other chemicals were purchased from Sinopharm Chemical Reagent Co. Ltd and used directly without further purification. 2.2 Preparation of RGHs and characterization. GO was synthesized from graphite powder (325 mesh) by a modified Hummers method, which possessed good dispersion in monolayered sheets as in our previous work [14]. The preparation process (Fig. S1) and characterization of RGHs can be found in the supplementary material. 3. Results and discussions
3
Fig. 1. The morphology of RGHs was characterized by field emission scanning electron microscopy (FESEM). As imaged by SEM images with different magnifications of freeze-dried samples, RGHs-1 (Fig. 1a-c), RGHs-2 (Fig. 1d-f) and RGHs-5 (Fig. 1g-i) showed typical 3D network and porous structures forming by wrinkling and folding of graphene sheets through π-π stacking and hydrophobic interactions. From the disappeared peak at 9.74° (6.94 Å) in GO and new broad bumps at 24.66, 23.77 and 24.34° which corresponding to interplanar spacing of 3.61, 3.74 and 3.65 Å for RGHs-1, RGHs-2 and RGHs-5 (Fig. 2a), it can be seen that the hydrogels have been formed. In order to confirm the reduction process, Raman spectra was carried out as shown in Fig. 2b. Two fundamental vibrations of D band at 1350 cm-1 and G band at 1597 cm-1 were clearly observed. The intensity ratio of ID/IG increased from 0.89 of GO to 0.97, 1.05 and 1.03 for RGHs-1, RGHs-2 and RGHs-5, indicating the removal of oxygenated groups. FT-IR spectra (Fig. 2c) showed that the broad band at 3000-3500 cm-1 related to hydroxyl groups (O-H) and peak at 1730 cm-1 related to carbonyl and carboxyl groups decreased dramatically in RGHs, further indicating the efficiently removal of the oxygen-contained groups. Moreover, the obvious increase of the peaks at
4
3128, 3039, 1549, 1398 and 1070 cm-1 attributed to stretching vibrations of C-H and C-C further illustrated the reduction of GO. A new peak at 1550 cm−1 corresponding to the N-H bending vibration appears, implying the doping of nitrogen in the reducing process. The element compositions of RGHs are determined by XPS measurement (Fig. 2d) and the content of different elements are listed in Table S2. Based on the XPS results, nitrogen doping of RGHs are confirmed, in which the N content of RGHs is in the range of 3.83-4.22 atm.%. Apparently, the decrease of O content and increase of C content in RGHs further confirm the reduction process.
Fig. 2. In order to investigate the atom binding states of the prepared materials, the high resolution XPS measurements were carried out as shown in Fig. 3, which showed the C1s, O1s and N1s deconvolution spectra of RGHs-1 (a, b, c), RGHs-2 (d, e, f) and RGHs-5 (h, i, j), respectively. In case of C1s of RGHs-1, four peaks at 284.8, 286.7, 287.0 and 288.8 eV corresponding to C=C/C-C in sp2-hybridized domains, C-O (epoxy and hydroxyl), C=O (carbonyl) and O=C-O (carboxyl) groups were observed. Besides, the appearance of the new characteristic peak corresponding to C-N bond (285.7 eV) indicates the successful doping of nitrogen. The N1s of RGHs-1 are determined by 5
398.7, 400.2 and 401.6 eV, which can be attributed to pyridinic N, pyrrolic N and graphitic N, respectively. In case of O1s of RGHs-1, three peaks of C-O (epoxy and hydroxyl), C=O (carbonyl), and O=C-O (carboxyl) groups are determined by the peaks at 531.8, 532.7 and 533.6 eV, respectively. All the high-resolution XPS spectra demonstrate the effective removal of oxygen-containing groups and doping of nitrogen by dimethyl ketoxime with ammonia in the reduction process.
Fig. 3. The electrochemical properties of the supercapacitor electrodes based on RGHs are investigated through cyclic voltammograms (CV). As shown in Fig. 4a-c and Fig. S2a, obvious current enlargement spread over a wide range of -0.4~-0.9 V on the CV curves of RGHs could be observed, indicating the existence of large pseudo-capacitance. The capacitive behavior was further tested by a galvanostatic charge/discharge experiment at different current density. From the discharge curve, the specific capacitance of the RGHs electrodes are evaluated to be 159.8, 215.1 and 163.4 F g−1 at 1 A g-1 for RGHs-1, RGHs-2 and RGHs-5, respectively (Fig. S2b). The specific capacitances of RGHs are further investigated with the increasing of charge/discharge current density. It can be seen that the specific capacitances decrease at high charging/discharging current density. 6
However, RGHs can still be maintained specific capacitances of 95.6, 155.2 and 118.9 F g-1 at a very high current density of 20 A g-1, the retention rates are 59.8, 72.2 and 72.8％ for RGHs-1, RGHs-2 and RGHs-5, respectively (Fig. 4d-f and Fig. S3a).
Fig. 4. Nyquist plots of RGHs in a frequency range from 10 mHz to 100 kHz were measured (Fig. S3b), which are composed of three distinct parts at different frequency range, including an uncompleted semicircle part at high frequency, an inclined portion of the curve (about 45°) at middle frequency and a linear part at low frequency. At very high frequencies, the imaginary impedance is near to zero and the corresponding real impedance (Z’) is the sum of ohmic resistances derived from the electrolyte and the contact between the electrode and the current collector. The 45° slope region at middle frequency can be attributed to the ions diffusion/transport from the electrolyte to the pore on the surface. The almost vertical line represents the dominance of ideal double-layer charge/discharge behaviors at low frequency. 4. Conclusions In summary, 3D reduced graphene hydrogels are prepared through an efficient and facile way by using dimethyl ketoxime as reducing and doping agents. Benefiting from 7
well-defined and cross-linked 3D porous network architectures, the supercapacitors based on the RGHs exhibited a high specific capacitance and good electrochemical stability in the repetitive charge/discharge cycling test, which indicating the good rate performance of the investigated RGHs ascribed to its porous structures and heteroatom-doped species. Acknowledgements We are grateful for the financial support from the National Natural Science Foundation of China (21402108), Shandong Natural Science Foundation (ZR2014BQ036) and Young Teacher Supporting Fund of Shandong University of Technology. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version. References
[1] Xu Y, Sheng K, Li C, Shi G. ACS Nano 2010;4:4324-30.
[2] Xu Y, Shi G, Duan X. Acc Chem Res 2015;48:1666-75.
[3] Li C, Shi G. Adv Mater 2014;26:3992-4012.
[4] Nardecchia S, Carriazo D, Ferrer ML, Gutierrez MC, del Monte F. Chem Soc Rev 2013;42:794-830.
[5] Cong H-P, Chen J-F, Yu S-H. Chem Soc Rev 2014;43:7295-325.
8
[6] Xu Y, Shi G. J Mater Chem 2011;21:3311-23.
[7] Jiang L, Fan Z. Nanoscale 2014;6:1922-45.
[8] Li C, Shi G. Nanoscale 2012;4:5549-63.
[9] Zhang X, Zhang H, Li C, Wang K, Sun X, Ma Y. RSC Adv 2014;4:45862-84.
[10] Luo B, Zhi L. Energy Environ Sci 2015;8:456-77.
[11] Wu X-L, Xu A-W. J Mater Chem A 2014;2:4852-64.
[12] Xia XH, Chao DL, Zhang YQ, Shen ZX, Fan HJ. Nano Today 2014;9:785-807.
[13] Su P, Guo H-L, Tian L, Ning S-K. Carbon 2012;50:5351-8.
[14] Xing L-B, Hou S-F, Zhou J, Li S, Zhu T, Li Z, et al. J Phys Chem C 2014;118:25924-30.
Figure Captions
Fig. 1. FESEM images of RGHs with different magnifications.
Fig. 2. XRD (a), Raman (b), FT-IR (c) spectra and XPS survey of GO and RGHs.
Fig. 3. High-resolution XPS spectra of C1s, O1s and N 1s of RGHs-1 (a-c), RGHs-2 (d-f) and RGHs-5 (g-i).
9
Fig. 4. Cyclic voltammograms of the supercapacitors based on RGHs at different scan rates (a-c); galvanostatic charge/discharge curves of RGHs at different charging/discharging current density (d-f).
10
Highlights
Three-dimensional reduced graphene hydrogels (RGHs) were prepared.
Dimethyl ketoxime was used as reducing and doping agents.
SEM showed typical three-dimensional network and porous structures.
RGHs electrodes exhibited a high specific capacitance in supercapacitors.
11