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Room temperature synthesis of reduced graphene oxide nanosheets as anode material for supercapacitors
Accepted Manuscript Room temperature synthesis of reduced graphene oxide nanosheets as anode material for supercapacitors Nagaraju Sykam, G. Mohan Rao PII: DOI: Reference:
S0167-577X(17)30836-4 http://dx.doi.org/10.1016/j.matlet.2017.05.114 MLBLUE 22689
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
25 October 2016 17 April 2017 25 May 2017
Please cite this article as: N. Sykam, G. Mohan Rao, Room temperature synthesis of reduced graphene oxide nanosheets as anode material for supercapacitors, Materials Letters (2017), doi: http://dx.doi.org/10.1016/j.matlet. 2017.05.114
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 proof before it is published in its final 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.
Room temperature synthesis of reduced graphene oxide nanosheets as anode material for supercapacitors Nagaraju Sykam* and G. Mohan Rao Department of Instrumentation, Indian Institute of Science, Bangalore, 560012, India
Abstract We report a facile approach to large scale synthesis of reduced graphene oxide (RGO) materials at room temperature with hydrazine hydrate. As-prepared GO and RGO materials were characterized by X-ray Photoelectron Spectroscopy, Raman spectroscopy, X-ray Diffraction, and scanning electron microscopy techniques. Electrochemical tests of RGO materials have been performed using cyclic voltammetry,
galvanostatic
charge-discharge
and
electrochemical
impedance
spectroscopy
measurements under aqueous solution. The maximum specific capacitance of 112.6 F g−1 for RGO material has been obtained to be at a current density of 1 A g−1 in 1M Na2SO4 electrolyte solution. The materials showed good cyclic stability up to 500 cycles and the degradation of the specific capacitance is only less than 3%. The simple approach and scalable synthesis of present study, is an efficient route to produce RGO sheets with low cost and is a promising material for potential supercapacitor applications. Keywords: Graphite oxide, reduced graphene oxide, supercapacitors, nanomaterials, energy. _____________________________________________________________________ *Corresponding author. Tel.: +91 80 22932349; fax: +91 80 23600135. E-mail address: [email protected].
1
1.
Introduction Supercapacitors are energy storage devices playing considerable attention due to ultrahigh power density, large rate capability and long cycling life time have been used in a various technological fields [1]. Graphene materials are proved to be excellent supercapacitor electrodes because of superior physico-chemical properties, high theoretical surface area, and excellent theoretical specific capacitance [2, 3], is a promising material for multifunctional applications [4-6]. Currently, various methods are being used to produce graphene, including micromechanical cleavage, chemical vapor deposition, liquid phase exfoliation of graphite, and the chemical reduction of graphite oxide (GO) [7-10]. Among all the methods, production of graphene by the chemical reduction of GO (reduced graphene oxide (RGO)) is one of the best methods for scalable production of RGO. In general, reduction of GO is carried out by one chemical reducing agent such as hydrazine hydrate followed by heat treatment. However, heat treatment is a difficult, as well as, time consuming process (12-24h for 80-100oC) [11-13]. In the present study, GO was prepared by modified hummer’s method. The RGO materials were prepared by the efficient reduction of GO with hydrazine hydrate at room temperature for 24h. The RGO electrode shows excellent electrochemical properties with high specific capacitance values.
2. 2.1.
Experimental Preparation of RGO GO was prepared with natural graphite powder (NGP) by the modified Hummers method [14].
The as prepared GO (2g) material was dispersed in 2L de-ionized water, and sonicated for 30min. Hydrazine hydrate (2mL) was added and the solution was kept for 24h at room temperature yielding a black coloured solution called reduced graphene oxide (RGO). Finally, the solution was filtered and dried at 80oC for 12h to form RGO powder. 2.2 Characterization The as prepared GO and RGO samples were characterized by field emission scanning electron microscope (FESEM; Zeiss EVO-50), X-ray photoelectron spectrometer (Phoibos 100 MCD Energy Analyser) using Al Kα radiation (1486.6 eV), laser Raman spectroscopy (LABRAM-HR800), X-ray diffraction (Bruker D8 Advance) with Cu Kα radiation. The electrochemical behavior of the RGO electrode was studied using cyclic voltammetry, galvanostatic charge discharge cycling and electrochemical impedance spectroscopy (EIS) in aqueous (1M Na2SO4) electrolyte in the potential
2
range of +0.0–1.0 V at room temperature by electrochemical workstation (Solatron Analytical). The RGO electrode was prepared according to the procedure discussed elsewhere [15]. 3.
Results and discussion X-ray photo electron spectroscopy (XPS) C1s spectrum of GO and RGO are shown in Fig.
1(a, b). It was observed that the intensity of oxygen functional groups present in GO (FIG. 1 (a)) is decreased drastically in RGO, as shown in Fig. 1(b), indicating the reduction of GO [16]. The C/O atomic ratio of GO and RGO is 2.35 and 9.82 respectively and it confirms the efficient reduction of oxygen functional groups with hydrazine hydrate at room temperature. Fig. 1(c) shows Raman spectra of GO and RGO samples which exhibits two bands called D and G. The G band exhibits at 1592 cm-1 for GO sample and is down shifted to 1586 cm-1 in case of RGO. The D band for GO exhibits at 1352 cm-1, and again is down shifted to 1347 cm-1, after reduction indicating the efficient reduction of GO by hydrazine hydrate at room temperature. Also, after successful reduction the intensity ratio of D to G band (ID/IG ) increases from 1.02 to 1.24. The increase in the ID/IG intensity ratio indicates disorder degree and structural defect in carbon materials [17]. The XRD patterns of GO and RGO are presented in Fig. 1(d). GO exhibits broad diffraction peak that appears at 9.18o with large increase in interlayer spacing of 9.62Å, when compared to the value of 3.35 Å of graphite [18]. It confirms the formation of oxygen functional groups, as well as, water molecules between the layers that results increasing the spacing (exfoliation) in hydrophilic GO. After reduction of GO, the RGO materials exhibit a broad peak at 26.40o with an interlayer spacing of 3.37Å, respectively. Fig. 2 shows the SEM micrographs of NGP, GO, and RGO materials. From Fig. 2(a), one can see a relatively flat surface of NGP particles. After successful chemical treatment of NGP, the strong layered structure of solid GO material and a flat surface morphology was observed with FESEM, as shown in Fig. 2(b). The stack of graphene oxide layers can be seen in the cross sectional morphology of GO, as shown in Fig. 2(c). Agglomeration of well exfoliated RGO sheets can be seen after reduction with hydrazine at room temperature, as shown in Fig. 2(d). The electrochemical performance of RGO as an electrode was studied by using cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS). CV analysis of the cell was carried out at a scan rate of 10-100 mV/s in 1M Na2SO4 electrolyte solution with the potential window of 0.0 to +1.0V, as shown in Fig. 3(a). It can be observed that the shape of
3
the CV curve changes from ideal rectangular to oval with increasing scan rate. This is may be due to the internal resistance of the electrode inhibiting the charge collection, limited diffusion of Na+ in the electrode as well as low conductivity of Na2SO4 in the aqueous solution [19]. Galvanostatic charge-discharge was carried out in 1M Na2SO4 at current densities of 1, 2, and 3 A/g between 0.0 and 1.0V to demonstrate the long-term stability of the RGO materials, as shown in Fig. 3 (b). The specific capacitance of the material was calculated from the charge-discharge experiments using the formula, Cspecific = I.t/V.m Where ‘I’ is the total current applied, ‘t’ is the discharging time, ‘V’ is the saturation potential, and ‘m’ is the mass of the active material in the electrode. The specific capacitance values of the RGO materials obtained from discharge curves at current densities of 1, 2, and 3A/g are 112.60, 110.9, and 108.2F/g, respectively. It can be observed that the specific capacitance of the electrode decreases slowly with increasing current density. EIS measurements of RGO electrode was carried out in the frequency range from 100 kHz to 0.01 Hz and is indicated by Nyquist plot, as shown in Fig. 3 (c). A nearly vertical straight line of impedance data at lower frequencies clearly indicates the good capacitive behavior of the electrodes. This good capacitive performance can be ascribed to the ion diffusive process taking place between the electrolytes into the electrode. A semicircular arc at higher frequencies is attributed to the double-layer capacitance, which is in parallel to the charge transfer resistance at the contact interface between electrode and electrolyte solution [20]. The cyclic stability performance of RGO electrode for 500 cycles was studied by charge-discharge cycle measurements at a current density of 1A/g between the potential 0.0 and 1.0 V. The decrease of specific capacitance of RGO electrode exhibit only less than 3% after 500 cycles, which indicates the excellent cyclic stability of RGO electrode, as shown in Fig. 3 (d). We Compared, our results with some of reported values of measured electrochemical capacitance with RGO materials, as shown in Table 1. When compared to the reduction of GO by various heating techniques, this process has several advantages like simple process, less energy consumption, low cost, and is a promising material for potential application in electrochemical supercapacitors. 4.
Conclusions
In this study, we demonstrated the efficient reduction of GO materials with hydrazine hydrate at room temperature. Room temperature reduction is an inexpensive, efficient and less energy consumption process for scalable production of RGO materials. The resultant GO and RGO materials were characterized by XPS, Raman, XRD, and SEM. The maximum specific capacitance of RGO material is
4
obtained as 112.6 F g−1 at a current density of 1 A g−1. The RGO material exhibits excellent cyclic stability after 500 cycles, only the attenuation of the specific capacitance is less than 3%, indicating that RGO electrode is a promising material for supercapacitors. This simple, inexpensive, and efficient production of RGO sheets are amenable to large scale production with low cost and promising for potential supercapacitors applications.
Refrences [1]. P. Simon, Y. Gogotsi et al. Nat. Mater 7 (2008) 845–54 [2] B.Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts JR, et al, Adv. Mater. 22 (2010) 3906–24. [3] J. Hu, Z. Kang, F. Li, X. Huang, Carbon 67 (2014) 221–9 [4] Q. Xiang, J. Yu, M. Jaronie, Chem. Soc. Rev. 41 (2012) 782–96. [5] F. Schwierz, Nat. Nanotechnol. 5 (2010) 487–96. [6] S. Bae, H. Kim, Y. Lee, X. Xu, J. Park, Y. Zheng, et al, Nat. Nanotechnol. 5 (2010) 574–8. [7] L.G. Kolla, B. Navakanta, and M. Sangeneni, Applied Physics Letters 103 (2013) 073105 [8] N. Sykam and K. K. Kar, Graphene 2 (2014) 52-56 [9] M. Ghosh, G. Venkatesh, G.M. Rao, Solid State Ionics 296 (2016) 31–36 [10] B. Yuan, Y. Shi, X. Mu, J. Wang, W. Xing, K. M. Lie, Y. Hu, Mater. Lett. 162 (2016) 154–156 [11] C. Nie, D. Liu, L. Pan, Y. Liu, Z. Sun, J. Shen, Solid State Ionics 247–248 (2013) 66–70 [12] S. Park, J. An, J.R. Potts, A. Velamakanni, S. Murali, R.S. Ruoff, Carbon 49 (2011) 3019–3023. [13] S. Stankovich, D.A. Dikin, G.H.B. Dommett, K.M. Kohlhaas, E.J. Zimney, E.A. Stach, et al, Nature 442 (2006) 282-286. [14] N. Sykam and G.M. Rao, Graphene 2 (2014) 28-33 [15] S. Shivakumara, K. Brij, P.T. Rao, N. Munichandraiah, Solid State Comm. 199 (2014) 26–32 [16] Z.G. Wang, P.J. Li, Y.F. Chen, J.R. He, B.J. Zheng, J.B. Liu, et al., Mater. Lett. 116 (2014) 416– 419. [17] Y.-F. Li, Y.-Z. Liu, W.-K. Zhang, C.-Y. Guo, C.-M. Chen, Mater. Lett. 157 (2015) 273–276. [18] C. Nethravathi, M. Rajamathi, Carbon 46 (2008) 1994–1998 [19] Z.P. Li, Y.J. Mi, X.H. Liu, et al. J. Mater. Chem. 2011;21:14706–11. [20] S.R.S. Prabaharan, R. Vimala, Z. Zainal, J. Power. Sources 161 (2006) 730.
5
[21] J. H. Lee, N. Park, B.G. Kim, D.S. Jung, K. Im, J. Hur and J.W. Choi, ACS Nano 7 (2013) 9366– 9374 Figure captions Fig. 1. XPS C1s spectrum of (a) GO, and (b) RGO materials, (c) Raman analysis of GO and RGO materials, and (d) XRD analysis of GO and RGO materials. Fig. 2. FESEM morphology of (a) NGP, (b) GO surface, (c) GO cross section, and (d) RGO surface. Fig. 3. (a) CV analysis, (b) galvanostatic charge-discharge, (c) EIS analysis (inset shows the semicircle at higher frequencies), and (d) cyclic stability of RGO electrode
6
Figure. 1.
Figure. 2.
7
Figure. 3.
Table 1. comparison of measured electrochemical capacitance with other RGO materials.
Electrode
Electrolyte
Current density/ scan rate
Specific capacitance (F/g)
Ref.
RGO RGO RGO RGO
1M KCl 1M Na2SO4 1M LiPF6 1M Na2SO4
5mV/s 0.5A/g 0.5A/g 1A/g
54.3 92 110 112.6
11 15 21 Present work
8
Highlights •
Simple and efficient reduction of GO at room temperature
•
Easy process, scalable, and low cost method for producing RGO materials
•
The RGO electrode shows excellent electrochemical properties
•
Achieved high specific capacitance value of 112.6F/g
•
The RGO electrode shows good cyclic stability up to 500 cycles
9
S0167-577X(17)30836-4 http://dx.doi.org/10.1016/j.matlet.2017.05.114 MLBLUE 22689
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
25 October 2016 17 April 2017 25 May 2017
Please cite this article as: N. Sykam, G. Mohan Rao, Room temperature synthesis of reduced graphene oxide nanosheets as anode material for supercapacitors, Materials Letters (2017), doi: http://dx.doi.org/10.1016/j.matlet. 2017.05.114
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 proof before it is published in its final 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.
Room temperature synthesis of reduced graphene oxide nanosheets as anode material for supercapacitors Nagaraju Sykam* and G. Mohan Rao Department of Instrumentation, Indian Institute of Science, Bangalore, 560012, India
Abstract We report a facile approach to large scale synthesis of reduced graphene oxide (RGO) materials at room temperature with hydrazine hydrate. As-prepared GO and RGO materials were characterized by X-ray Photoelectron Spectroscopy, Raman spectroscopy, X-ray Diffraction, and scanning electron microscopy techniques. Electrochemical tests of RGO materials have been performed using cyclic voltammetry,
galvanostatic
charge-discharge
and
electrochemical
impedance
spectroscopy
measurements under aqueous solution. The maximum specific capacitance of 112.6 F g−1 for RGO material has been obtained to be at a current density of 1 A g−1 in 1M Na2SO4 electrolyte solution. The materials showed good cyclic stability up to 500 cycles and the degradation of the specific capacitance is only less than 3%. The simple approach and scalable synthesis of present study, is an efficient route to produce RGO sheets with low cost and is a promising material for potential supercapacitor applications. Keywords: Graphite oxide, reduced graphene oxide, supercapacitors, nanomaterials, energy. _____________________________________________________________________ *Corresponding author. Tel.: +91 80 22932349; fax: +91 80 23600135. E-mail address: [email protected].
1
1.
Introduction Supercapacitors are energy storage devices playing considerable attention due to ultrahigh power density, large rate capability and long cycling life time have been used in a various technological fields [1]. Graphene materials are proved to be excellent supercapacitor electrodes because of superior physico-chemical properties, high theoretical surface area, and excellent theoretical specific capacitance [2, 3], is a promising material for multifunctional applications [4-6]. Currently, various methods are being used to produce graphene, including micromechanical cleavage, chemical vapor deposition, liquid phase exfoliation of graphite, and the chemical reduction of graphite oxide (GO) [7-10]. Among all the methods, production of graphene by the chemical reduction of GO (reduced graphene oxide (RGO)) is one of the best methods for scalable production of RGO. In general, reduction of GO is carried out by one chemical reducing agent such as hydrazine hydrate followed by heat treatment. However, heat treatment is a difficult, as well as, time consuming process (12-24h for 80-100oC) [11-13]. In the present study, GO was prepared by modified hummer’s method. The RGO materials were prepared by the efficient reduction of GO with hydrazine hydrate at room temperature for 24h. The RGO electrode shows excellent electrochemical properties with high specific capacitance values.
2. 2.1.
Experimental Preparation of RGO GO was prepared with natural graphite powder (NGP) by the modified Hummers method [14].
The as prepared GO (2g) material was dispersed in 2L de-ionized water, and sonicated for 30min. Hydrazine hydrate (2mL) was added and the solution was kept for 24h at room temperature yielding a black coloured solution called reduced graphene oxide (RGO). Finally, the solution was filtered and dried at 80oC for 12h to form RGO powder. 2.2 Characterization The as prepared GO and RGO samples were characterized by field emission scanning electron microscope (FESEM; Zeiss EVO-50), X-ray photoelectron spectrometer (Phoibos 100 MCD Energy Analyser) using Al Kα radiation (1486.6 eV), laser Raman spectroscopy (LABRAM-HR800), X-ray diffraction (Bruker D8 Advance) with Cu Kα radiation. The electrochemical behavior of the RGO electrode was studied using cyclic voltammetry, galvanostatic charge discharge cycling and electrochemical impedance spectroscopy (EIS) in aqueous (1M Na2SO4) electrolyte in the potential
2
range of +0.0–1.0 V at room temperature by electrochemical workstation (Solatron Analytical). The RGO electrode was prepared according to the procedure discussed elsewhere [15]. 3.
Results and discussion X-ray photo electron spectroscopy (XPS) C1s spectrum of GO and RGO are shown in Fig.
1(a, b). It was observed that the intensity of oxygen functional groups present in GO (FIG. 1 (a)) is decreased drastically in RGO, as shown in Fig. 1(b), indicating the reduction of GO [16]. The C/O atomic ratio of GO and RGO is 2.35 and 9.82 respectively and it confirms the efficient reduction of oxygen functional groups with hydrazine hydrate at room temperature. Fig. 1(c) shows Raman spectra of GO and RGO samples which exhibits two bands called D and G. The G band exhibits at 1592 cm-1 for GO sample and is down shifted to 1586 cm-1 in case of RGO. The D band for GO exhibits at 1352 cm-1, and again is down shifted to 1347 cm-1, after reduction indicating the efficient reduction of GO by hydrazine hydrate at room temperature. Also, after successful reduction the intensity ratio of D to G band (ID/IG ) increases from 1.02 to 1.24. The increase in the ID/IG intensity ratio indicates disorder degree and structural defect in carbon materials [17]. The XRD patterns of GO and RGO are presented in Fig. 1(d). GO exhibits broad diffraction peak that appears at 9.18o with large increase in interlayer spacing of 9.62Å, when compared to the value of 3.35 Å of graphite [18]. It confirms the formation of oxygen functional groups, as well as, water molecules between the layers that results increasing the spacing (exfoliation) in hydrophilic GO. After reduction of GO, the RGO materials exhibit a broad peak at 26.40o with an interlayer spacing of 3.37Å, respectively. Fig. 2 shows the SEM micrographs of NGP, GO, and RGO materials. From Fig. 2(a), one can see a relatively flat surface of NGP particles. After successful chemical treatment of NGP, the strong layered structure of solid GO material and a flat surface morphology was observed with FESEM, as shown in Fig. 2(b). The stack of graphene oxide layers can be seen in the cross sectional morphology of GO, as shown in Fig. 2(c). Agglomeration of well exfoliated RGO sheets can be seen after reduction with hydrazine at room temperature, as shown in Fig. 2(d). The electrochemical performance of RGO as an electrode was studied by using cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS). CV analysis of the cell was carried out at a scan rate of 10-100 mV/s in 1M Na2SO4 electrolyte solution with the potential window of 0.0 to +1.0V, as shown in Fig. 3(a). It can be observed that the shape of
3
the CV curve changes from ideal rectangular to oval with increasing scan rate. This is may be due to the internal resistance of the electrode inhibiting the charge collection, limited diffusion of Na+ in the electrode as well as low conductivity of Na2SO4 in the aqueous solution [19]. Galvanostatic charge-discharge was carried out in 1M Na2SO4 at current densities of 1, 2, and 3 A/g between 0.0 and 1.0V to demonstrate the long-term stability of the RGO materials, as shown in Fig. 3 (b). The specific capacitance of the material was calculated from the charge-discharge experiments using the formula, Cspecific = I.t/V.m Where ‘I’ is the total current applied, ‘t’ is the discharging time, ‘V’ is the saturation potential, and ‘m’ is the mass of the active material in the electrode. The specific capacitance values of the RGO materials obtained from discharge curves at current densities of 1, 2, and 3A/g are 112.60, 110.9, and 108.2F/g, respectively. It can be observed that the specific capacitance of the electrode decreases slowly with increasing current density. EIS measurements of RGO electrode was carried out in the frequency range from 100 kHz to 0.01 Hz and is indicated by Nyquist plot, as shown in Fig. 3 (c). A nearly vertical straight line of impedance data at lower frequencies clearly indicates the good capacitive behavior of the electrodes. This good capacitive performance can be ascribed to the ion diffusive process taking place between the electrolytes into the electrode. A semicircular arc at higher frequencies is attributed to the double-layer capacitance, which is in parallel to the charge transfer resistance at the contact interface between electrode and electrolyte solution [20]. The cyclic stability performance of RGO electrode for 500 cycles was studied by charge-discharge cycle measurements at a current density of 1A/g between the potential 0.0 and 1.0 V. The decrease of specific capacitance of RGO electrode exhibit only less than 3% after 500 cycles, which indicates the excellent cyclic stability of RGO electrode, as shown in Fig. 3 (d). We Compared, our results with some of reported values of measured electrochemical capacitance with RGO materials, as shown in Table 1. When compared to the reduction of GO by various heating techniques, this process has several advantages like simple process, less energy consumption, low cost, and is a promising material for potential application in electrochemical supercapacitors. 4.
Conclusions
In this study, we demonstrated the efficient reduction of GO materials with hydrazine hydrate at room temperature. Room temperature reduction is an inexpensive, efficient and less energy consumption process for scalable production of RGO materials. The resultant GO and RGO materials were characterized by XPS, Raman, XRD, and SEM. The maximum specific capacitance of RGO material is
4
obtained as 112.6 F g−1 at a current density of 1 A g−1. The RGO material exhibits excellent cyclic stability after 500 cycles, only the attenuation of the specific capacitance is less than 3%, indicating that RGO electrode is a promising material for supercapacitors. This simple, inexpensive, and efficient production of RGO sheets are amenable to large scale production with low cost and promising for potential supercapacitors applications.
Refrences [1]. P. Simon, Y. Gogotsi et al. Nat. Mater 7 (2008) 845–54 [2] B.Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts JR, et al, Adv. Mater. 22 (2010) 3906–24. [3] J. Hu, Z. Kang, F. Li, X. Huang, Carbon 67 (2014) 221–9 [4] Q. Xiang, J. Yu, M. Jaronie, Chem. Soc. Rev. 41 (2012) 782–96. [5] F. Schwierz, Nat. Nanotechnol. 5 (2010) 487–96. [6] S. Bae, H. Kim, Y. Lee, X. Xu, J. Park, Y. Zheng, et al, Nat. Nanotechnol. 5 (2010) 574–8. [7] L.G. Kolla, B. Navakanta, and M. Sangeneni, Applied Physics Letters 103 (2013) 073105 [8] N. Sykam and K. K. Kar, Graphene 2 (2014) 52-56 [9] M. Ghosh, G. Venkatesh, G.M. Rao, Solid State Ionics 296 (2016) 31–36 [10] B. Yuan, Y. Shi, X. Mu, J. Wang, W. Xing, K. M. Lie, Y. Hu, Mater. Lett. 162 (2016) 154–156 [11] C. Nie, D. Liu, L. Pan, Y. Liu, Z. Sun, J. Shen, Solid State Ionics 247–248 (2013) 66–70 [12] S. Park, J. An, J.R. Potts, A. Velamakanni, S. Murali, R.S. Ruoff, Carbon 49 (2011) 3019–3023. [13] S. Stankovich, D.A. Dikin, G.H.B. Dommett, K.M. Kohlhaas, E.J. Zimney, E.A. Stach, et al, Nature 442 (2006) 282-286. [14] N. Sykam and G.M. Rao, Graphene 2 (2014) 28-33 [15] S. Shivakumara, K. Brij, P.T. Rao, N. Munichandraiah, Solid State Comm. 199 (2014) 26–32 [16] Z.G. Wang, P.J. Li, Y.F. Chen, J.R. He, B.J. Zheng, J.B. Liu, et al., Mater. Lett. 116 (2014) 416– 419. [17] Y.-F. Li, Y.-Z. Liu, W.-K. Zhang, C.-Y. Guo, C.-M. Chen, Mater. Lett. 157 (2015) 273–276. [18] C. Nethravathi, M. Rajamathi, Carbon 46 (2008) 1994–1998 [19] Z.P. Li, Y.J. Mi, X.H. Liu, et al. J. Mater. Chem. 2011;21:14706–11. [20] S.R.S. Prabaharan, R. Vimala, Z. Zainal, J. Power. Sources 161 (2006) 730.
5
[21] J. H. Lee, N. Park, B.G. Kim, D.S. Jung, K. Im, J. Hur and J.W. Choi, ACS Nano 7 (2013) 9366– 9374 Figure captions Fig. 1. XPS C1s spectrum of (a) GO, and (b) RGO materials, (c) Raman analysis of GO and RGO materials, and (d) XRD analysis of GO and RGO materials. Fig. 2. FESEM morphology of (a) NGP, (b) GO surface, (c) GO cross section, and (d) RGO surface. Fig. 3. (a) CV analysis, (b) galvanostatic charge-discharge, (c) EIS analysis (inset shows the semicircle at higher frequencies), and (d) cyclic stability of RGO electrode
6
Figure. 1.
Figure. 2.
7
Figure. 3.
Table 1. comparison of measured electrochemical capacitance with other RGO materials.
Electrode
Electrolyte
Current density/ scan rate
Specific capacitance (F/g)
Ref.
RGO RGO RGO RGO
1M KCl 1M Na2SO4 1M LiPF6 1M Na2SO4
5mV/s 0.5A/g 0.5A/g 1A/g
54.3 92 110 112.6
11 15 21 Present work
8
Highlights •
Simple and efficient reduction of GO at room temperature
•
Easy process, scalable, and low cost method for producing RGO materials
•
The RGO electrode shows excellent electrochemical properties
•
Achieved high specific capacitance value of 112.6F/g
•
The RGO electrode shows good cyclic stability up to 500 cycles
9