Accepted Manuscript Graphene- Zinc oxide (G-ZnO) nanocomposite for Electrochemical Supercapacitor Applications Murugan Saranya, Rajendran Ramachandran, Fei Wang PII:
S2468-2179(16)30161-7
DOI:
10.1016/j.jsamd.2016.10.001
Reference:
JSAMD 63
To appear in:
Journal of Science: Advanced Materials and Devices
Received Date: 12 September 2016 Accepted Date: 6 October 2016
Please cite this article as: M. Saranya, R. Ramachandran, F. Wang, Graphene- Zinc oxide (G-ZnO) nanocomposite for Electrochemical Supercapacitor Applications, Journal of Science: Advanced Materials and Devices (2016), doi: 10.1016/j.jsamd.2016.10.001. 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.
ACCEPTED MANUSCRIPT
Graphene- Zinc oxide (G-ZnO) nanocomposite for Electrochemical Supercapacitor Applications
b
Platinum Retail Ltd, Chorleywood Road, Rickmansworth, United Kingdom.
Department of Electrical and Electronic Engineering, Southern University of Science and
Technology, Shenzhen-518005, China Corresponding author mail id:
[email protected]
M AN U
*
SC
a
RI PT
Murugan Saranya a*, Rajendran Ramachandran b, Fei Wang b
Abstract:
Graphene-ZnO nanocomposites (G-ZnO) were prepared by a facile solvothermal approach. Well crystalline ZnO nanoparticles with size ~150 nm are uniformly dispersed on the graphene
TE D
sheets, as evidenced by different techniques. The electrochemical properties of the prepared nanocomposites were studied by measuring the specific capacitance in 6M KOH solution using cyclic voltammetry and galvanostatic charge discharge techniques. G-ZnO nanocomposite
EP
exhibited a good capacitive behavior with a specific capacitance of 122.4 F/g as compared to graphene oxide (2.13 F/g) and rGO (102.5 F/g) at 5 mV/s scan rate. Results demonstrated that
AC C
such hybrid materials are promising electrode materials for high performance supercapacitor applications.
Keywords: Solvothermal, Graphene-ZnO, Graphene Oxide, Cyclic Voltammetry, Specific capacitance.
ACCEPTED MANUSCRIPT
I. Introduction Supercapacitors are charge storage devices of tremendous interest in view of its high power density, fast charging/discharging rate, long cycle life, a wide operating temperature range and
RI PT
environmentally benign. Still the low energy density of these supercapacitors has imposed significant challenges in utilizing them as primary energy sources to replace batteries [1]. Hence continuous effort have been undertaken to use nanostructured materials with improved specific
SC
capacitance. Most research are focused on the development of different electrode materials like carbon, conducting polymers, metal oxides and out of which carbon based materials like
M AN U
activated carbon, carbon nanotube and carbon aerogels is paid more attention for energy storage devices [2]. Activated carbon and carbon nanotube exhibits good electrical double layer capacitance due to their excellent conductivity and high surface area, where the storage process is non-Faradaic and the storage of energy is electrostatic. The key to achieve high capacitance is
TE D
increase the surface area and electrical conductivity of the material. Recently graphene has been the most promising material for energy storage applications due its high conductivity, superior chemical stability, unique mechanical strength and large surface to volume ratio than other
EP
carbon materials [3]. Supercapacitors are categorized into two types based on the charge storage mechanism viz. electric double layer capacitors (EDLCs) and pseudocapacitor. The latter stores
AC C
charges faradically, which allows them to achieve higher capacitance properties and enhanced energy densities than EDLCs. Polymers and metal oxides like NiO [4], RuO2 [5], MnO2 [6], Co3O4 [7], and V2O5 [8] exhibit this type of capacitance called pseudocapacitance which involves redox reactions and often the pseudocapacitance of such polymers and metal oxides show higher specific capacitance than EDLCs. However, the relatively low conductivity and poor stability of such materials usually requires the addition of conductive phases e.g. carbon based to enhance
ACCEPTED MANUSCRIPT
the charge transfer. Thus these two could be merged together for the fabrication of a hybrid capacitor, where both faradaic and non-faradaic processes can be utilized for charge storage and enhanced electrochemical properties. It has been reported that the combination of carbon
RI PT
material with polymer/metal oxides or both exhibit higher specific capacitance due to the combination of redox reaction of metal oxide and high surface area/conductivity of graphene than their individual form due to a positive synergistic effect [9]. In the last few years, graphene
SC
based composites are being investigated for supercapacitor applications. In general, the specific capacitance of graphene is lesser than the expected value due to restacking of the graphene
M AN U
sheets which could be improved by making it as a composite with other materials. Wu et al have reported a maximum specific capacitance of 210 F/g for graphene-polyaniline composite [10]. Among the metal oxides, RuO2 exhibits higher specific capacitance but its usage is limited due to its high cost and toxicity. Thus, the fabrication of supercapacitor electrode materials with low
TE D
cost production is challenging in the field of energy storage devices and hence it is imperative to explore more desirable materials for supercapacitor applications. Zinc oxide (ZnO) is a potential semiconductor material with an excellent optical and electrical property. Due to this, it is widely
EP
used in many applications ranging from optoelectronics, sensors, energy storage and solar cells [11]. Though many works are reported for ZnO/Graphene as supercapacitor electrode, the
AC C
specific capacitance values are low. Herein we report a facile approach to synthesize ZnO/Graphene nanocomposites by solvothermal process. These composites were used to fabricate supercapacitor electrodes to probe their electrochemical properties and results revealed that the nanocomposite materials had a good electrochemical performance as electrode materials with a specific capacitance of 122.4 F/g.
ACCEPTED MANUSCRIPT
II. Materials and Experimental
RI PT
Materials. Graphite powder, sodium nitrate, potassium permanganate, hydrogen peroxide, sodium hydroxide, potassium hydroxide, ethylene glycol and zinc acetate were purchased from Sigma Aldrich. All the materials were used as received without any further purification.
SC
Preparation of graphene oxide. Graphene oxide was prepared through modified Hummer’s method as described in literature [12]. Graphite powder (1 g) and sodium nitrate (1 g) were
M AN U
mixed with 46 ml of concentrated sulfuric acid. The mixture was kept in an ice bath for four hours under continuous stirring. To it, potassium permanganate (6 g) was added and the reaction was then allowed at 35oC for two hours and diluted with 92 ml de-ionized water. Then the temperature was raised to 98oC and maintained for two hours. The solution was further diluted
TE D
with 200 ml warm water and 20 ml hydrogen peroxide and further stirred for another one hour. After the reaction, the color of the solution turned into yellowish brown, which was centrifuged (Eppendorf centrifuge 5430, 460W, Germany) at 7500 rpm with de ionized water and dried at
EP
60o C for 24 h.
AC C
Synthesis of G-ZnO nanocomposites. Graphene-ZnO nanocomposites were prepared according to our previously reported solvothermal method as described in the literature [13]. In brief, GO (5 mg) was dissolved in 20 ml of ethylene glycol and sonicated for 1 hour. Then 20 mg of zinc acetate dissolved in 20 ml of ethylene glycol was added to the above GO dispersed solution under continuous stirring. Later 0.1 M NaOH in 5 ml of distilled water was added to the mixture. After 30 min of stirring, the mixture was transferred into the teflon lined stainless steel autoclave and maintained at160oC for 48 h. The obtained final mixture was centrifuged and
ACCEPTED MANUSCRIPT
washed with de ionized water and ethanol several times, and dried at 60o C for 24 h. The weight of graphene in G-ZnO composite is 2 wt%. Electrochemical measurements. Cyclic voltammetry and choronopotentiometric experiments
RI PT
were investigated by using CHI 600C electrochemical work station in a three electrode system. Glassy carbon electrode, Ag/AgCl, and platinum wire electrode were used as working, reference
KOH electrolyte in the potential range from 0 to -0.8 V.
SC
and counter electrodes respectively. The experiment was carried out at room temperature in 6M
Electrode Preparation: The fabrication of the modified working electrode, glassy carbon was
M AN U
polished with 0.03 µm alumina powder, rinsed thoroughly with de ionized water, sonicated with ethanol and deionized water for 5 mins. After few minutes, 0.5 mg of the active material (GZnO, GO, rGO) in 2 µL nafion solution was coated on GC electrode (geometric surface area of the electrode is 0.0706 cm2) and allowed to dry at room temperature for few hours.
TE D
Characterization. The X-ray diffraction system (BRUKER, D8 Advance, Germany) was used for the X-ray analysis with Cu-Kα radition (λ=1.540 Å). Step scanning was used with 2θ intervals from 8° to 60°. Scanning Electron Microscope images were taken from the system (FEI
EP
Quanta FEG 200).The electrochemical performance were done by the system CHI600C work station, Version 5.01.
AC C
III. Results and discussion: A. Structural analysis
XRD pattern of pure graphite, graphene oxide and G-ZnO composite are shown in Fig 1.
The major peak of graphite is seen at 2θ=25.5° with an interlayer distance of 3.4 Å. After oxidation, the peak was observed at 2θ=10° in GO showing the perfect oxidation and the interlayer distance of graphene is 8.8 Å [14]. The increased interlayer distance is due to the
ACCEPTED MANUSCRIPT
intercalation of oxygen functional groups during oxidation process. There are five major peaks in G-ZnO composite at 2θ value 31.8°, 34.4°, 36.2°, 47.5°and 56.5° which correspond to (100), (002), (101), (102) and (110) crystalline plane of ZnO respectively. These crystalline planes are
RI PT
indexed to the wurtzite structure of ZnO particles matched with the JCPDS No.36-1451[15]. The average ZnO crystalline size as calculated from Scherrer formula was 14 nm. Apart from the ZnO peaks graphene peak could be seen at 2θ =24.5°. It shows that the inter layer distance
SC
between the graphene sheet is 3.6 Å, which is slightly larger than the layer distance of natural graphite indicating small amount of oxygen functional groups may be present in the graphene
M AN U
sheets[16].
The electronic structure of the G-ZnO nanocomposite was measured by UV diffusive reflectance spectroscopy, as shown in Fig. 2(a). It is observed that the graphene-ZnO composite exhibits a strong peak at 398 nm due to ZnO particles in graphene sheets [17]. Compared to GO,
TE D
G-ZnO composite has a strong peak at 271 nm, which indicates the excitation of π- plasmon graphitic structure [18]. The optical band gap is obtained by the following equation, with the
(αhν ) n = A (hν − E g )
AC C
EP
help of absorption spectra.
where ‘α’ is the absorption coefficient, ‘h’ is Planck constant, ‘υ’ is the light frequency, ‘Eg’ is the band gap, ‘n’ is either ½ for an indirect transition or 2 for a direct transition and A is a constant. According to the above equation the band gap of the as-obtained ZnO-Graphene nanocomposites is 3.12 eV, which is shown in Fig 2(b).
The FTIR spectrum of GO and G-ZnO composite are shown in Fig 3. It is observed that the oxygen functional groups of GO are revealed by the peaks at 1726, 1217 and 1055 cm-1
ACCEPTED MANUSCRIPT
corresponding to C=O stretching, C-O stretching and C-O bending [19][20] respectively. These oxygen functional groups are generated during the oxidation process of the graphite by Hummer’s method [21]. In the case of G-ZnO composite, it could be observed that the oxygen
RI PT
functional groups were almost reduced, which is indicating the reduction of GO during hydrothermal process. The absorbance peak at 1581 and 450 cm-1 indicated the skeletal vibration of graphene sheets and stretching vibration of Zn-O [20]. Thus these results indicate the
SC
formation of ZnO on graphene matrix. To further know the morphology of these nanostructures, SEM was recorded and the corresponding images are given in Fig 4. It can be seen that the
M AN U
wrinkled structure of graphene sheets are well decorated with ZnO nanoparticles with an average particle size of 150 nm along with a few nanorods.
B. Electrochemical Measurements:
The capacitive performances of the materials were further evaluated by cyclic voltammetry (CV)
TE D
and galvanostatic charge/discharge techniques in 6 M KOH electrolyte. The CV was run at different scan rates in the potential ranging from 0 to -0.8 V in 6M KOH electrolyte (Fig 5). The
EP
shapes of the CV loop in our experiment exhibit quasi-rectangular shape indicating the capacitive behavior of the capacitor [22]. As seen from the Fig, though the curve is partially
AC C
rectangular, it shows deviation from ideal rectangular shape with some redox peaks due to Faradaic reaction of ZnO, which indicates the pseudocapacitive nature of the material. Also could be observed from the Fig is that as compared to GO, the addition of ZnO to the graphene gives a better and a symmetric curve. From the Fig 6, it can be seen that the current level and area of CV curves is higher for G-ZnO nanocomposite than rGO and GO, which is indicates more capacitive nature of electrode. The possible faradic process can be explained as follows, ZnO + OH − ↔ ZnOOH + e −
ACCEPTED MANUSCRIPT
As the scan rate increases, the total peak current also increases demonstrating the good rate properties and capacitance behavior. The specific capacitance of the composite is calculated from the following equation [23] [12], (I + − I − ) mν
RI PT
C=
Where, I+ is maximum current in the positive scan (A), I- is maximum current in the negative
SC
scan (A), m is the mass of the active material (g) and υ is the scan rate (V/s). The specific capacitance is proportional to the area under the CV curve, which is larger for G-ZnO than GO
M AN U
and rGO. A maximum specific capacitance of 122.4 F/g was obtained at a scan rate 5 mV/s for G-ZnO which is higher than that of rGO (102.5 F/g) and GO (2.13 F/g) respectively. The high specific capacitance achieved in the G-ZnO may be due to effective electrical and ionic conductivity. Fig 7 shows the plot of scan rate versus specific capacitance and from the graph, it
TE D
is evident that the specific capacitance decreases at higher scan rates, which could be due to the presence of inner active sites that cannot sustain the redox transitions. Also this decrement indicates that the parts of the surface of the electrode are inaccessible at high
EP
charging/discharging rates. It shows that the G-ZnO composites could be used for high performance supercapacitor applications. A comparison has been given in Table 1 on the specific
AC C
capacitance of the present work with other reported materials. The galvanostatic charge/discharge is a reliable technique to evaluate the electrochemical capacitance of materials under controlled current conditions. Fig 8 demonstrates the chargedischarge behavior of GO and G-ZnO composite at a constant current of 0.1A/g. Both curves exhibited a near triangular shape and typical features of potential charge/discharge viz. linear response to time with asymmetric capacitive behavior during discharge process. Sudden drop in current at the starting of discharge is due to the internal resistance of electrode material [28]. It
ACCEPTED MANUSCRIPT
can be seen that the IR drop of GO is much higher than G-ZnO, which indicates the larger electrode/electrolyte interfacial resistance in the former. Low internal resistances are important for energy storage devices and less energy will be wasted to produce unwanted heat during
RI PT
charge/discharge processes. A discharge time of 130 seconds has been noticed for G-ZnO electrode which is higher than GO discharge time 7.5 seconds. A high discharge time is a clear evidence for high specific capacitance of G-ZnO electrode. These results are in accordance with
SC
the CV measurements.
Electrochemical impedance analysis is an informative technique to evaluate the properties of
M AN U
conductivity and charge transport in the electrode/electrolyte interface. Fig 9 shows the Nyquist plot and equivalent fitting circuit of GO and G-ZnO electrodes. In low frequency region, the impedance plot is increased sharply and tends to become vertical which is due to the capacitive nature of electrode. The 45o straight line can be observed in Fig 9(b) shows the pure capacitance
TE D
behavior of G-ZnO. The intercept of higher frequency on X axis yields the electrolyte resistance (Rs) and the diameter of semicircle yields the charge transfer resistance (Rct) [28]. A small electrolyte resistance of 12.2 Ω was observed for G-ZnO than GO (107.2 Ω) which is due to the
EP
excellent conductivity of graphene sheets in ZnO. The Warburg impedance can be observed in G-ZnO electrode related to the diffusional impedance of the electrochemical systems. Thus the
AC C
EIS analysis clearly demonstrated that the graphene-ZnO composite provide easier access of charge between electrode and electrolyte and hence a maximum specific capacitance have been achieved. These results suggested that the G-ZnO electrode could be used for high performance supercapacitor applications. IV. Conclusion: In summary, XRD shows wurtzite structure of ZnO and a particle size of ~150 nm as observed
ACCEPTED MANUSCRIPT
from SEM analysis. The electrochemical behavior of composite was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammetry results show a maximum specific capacitance of 122.4 F/g for G-ZnO composite electrode at 5 mV scan rate.
RI PT
The enhanced specific capacitance is due to the synergistic effect of ZnO and graphene in the composite materials. EIS analysis of composite shows the low resistance and hence easy access of ions towards the maximum specific capacitance. This suggested that the G-ZnO composite
SC
electrode is a promising material for supercapacitor applications. Acknowledgement
M AN U
This work was completed with financial support from the Platinum Retails Ltd., UK. References:
1. H. Wang, J. Lin, Z.X. Shen, Polyaniline (PANi) based electrode materials for energy storage and conversion, J. Sci: Adv. Mater. Devices, 2016 (In Press).
TE D
2. Y. Zhang, X. Sun, L. Pan, H. Li, Z. Sun, C. Sun, B. KangTay, Carbon nanotube–ZnO nanocomposite electrodes for supercapacitors, Solid State Ionics, 2009, 180, 1525-1528. 3. W.T. Song, J. Xie, S.Y. Liu, Y.X. Zheng, G.S. Cao, T.J. Zhu, X.B. Zhao, Graphene decorated
EP
with ZnO Nanocrystals with Improved Electrochemical Properties Prepared by a Facile In Situ Hydrothermal Route, Int.J. Electochem.Sci., 2012,7, 2164-2174.
AC C
4. D.W. Wang, F. Li, F. H. Cheng, Hierarchical porous nickel oxide and carbon as electrode materials for asymmetric supercapacitor, J. Power Sources, 2008, 185, 1563-1568. 5. J. Shen, T. Li, W. Huang, Y. Long, N. Li, M. Ye,
One-pot polyelectrolyte assisted
hydrothermal synthesis of RuO2-reduced graphene oxide nanocomposites, Electrochimi. Acta, 2013, 95, 155-161. 6. Y.F. Yuan, Y.B. Pei, S.Y. Guo, J. Fang, J.L. Yang, Sparse MnO2 nanowires clusters for high
ACCEPTED MANUSCRIPT
performance supercapacitors, Mat. Lett., 2012, 73,194-197. 7. S.K. Meher, G.R. Rao, Ultralayered Co3O4 for high performance Supercapacitor Applications, J. Phys. Chem C., 2011, 115, 15646-15654.
RI PT
8. Z.J. Lao, K. Konstantinov, Y. Tournaire, S.K. Ng, G.X. Wang, H.K. Liu, Synthesis of vanadium pentoxide powders with enhanced surface area for electrochemical capacitors, J. Power sources, 2006, 162, 1451-1454.
SC
9. G. Yu, X. Xie, L. Pan, Z. Bao, Y. Cui, Hybrid nanostructured materials for high-performance electrochemical capacitors” Nano Energy, 2012, 2, 213-234.
M AN U
10. Q. Wu, Y. Xu, Z. Yao, Y. Liu, G. Shi, Supercapacitors Based on Flexible Graphene/Polyaniline Nanofiber Composite Films, ACS Nano, 2010, 4, 1963-1970. 11. K.K. Purushothaman, V. Suba priya, S. Nagamuthu, S. Vijayakumar, G. Muralidharan, Synthesising of ZnO nanopetals for supercapacitor applications, Micro and Nano Lett., 2011, 6,
TE D
668-670.
12. R. Ramachandran, S. Felix, G.M. Joshi, B.P.C. Ragupathy, S.K. Jeong, A.N. Grace, Synthesis of Graphene platelets by chemical and electrochemical route, Mater. Res. Bull. 2013,
EP
48, 3834-3842.
13. M. Saranya, G. Srishti, I. Singh, R. Ramachandran, C. Santhosh, C. M.
BhanuChandra,
AC C
T.M. Vanchinathan,
A.N.
Grace,
Solvothermal
Harish,
Preparation
of
ZnO/Graphene Nanocomposites and Its Photocatalytic Properties, Nanosci. Nanotechnol.Lett., 2013, 5, 349-355.
14. A.K. Mishra, S. Ramprabhu, Functionalized graphene sheets for arsenic removal and desalination of sea water, Desalination, 2011, 228, 39-45. 15. H. Zeng, Y. Cao, J. Yang, Z. Tang, X. Wang, L. Sun, Synthesis, optical and electrochemical
ACCEPTED MANUSCRIPT
properties of ZnO nanowires/graphene oxide heterostructures, Nanoscale Res. Lett., 2013, 8, 133- 139. 16. J. Wangn, Z. Gao, Z. Li, B. Wang, Y. Yan, Q. Liu, T. Mann, M. Zhang, Z. Jiang, Green
RI PT
synthesis of graphene nanosheets/ZnO composites and Electrochemical properties, J. Solid State Chem,, 2011,184, 1421-1427.
17. T. Lu, L. Pan, H. Li, G. Zhu, T. Lv, X. Liu, Z. Sun, T. Chen, D.H.C. Chua, Microwave-
SC
assisted synthesis of graphene–ZnO nanocomposite for Electrochemical supercapacitors, J. Alloy. Compd., 2011, 509, 5488-5492.
M AN U
18. J. Wua, S. Baia, X. Shen, L. Jiang, Preparation and characterization of graphene/CdS nanocomposites, Appl. Surf. Sci., 2010, 257, 747-751.
19. C. Xu, X. Wang, L. Yang, Y. Wu, Fabrication of a graphene–cuprous oxide composite, J. Solid State Chem,2009, 182, 2486-2490.
TE D
20. J. Wu, X. Shen, L. Jiang, K. Wang, K. Chen, Solvothermal synthesis and characterization of sandwich-like graphene/ZnO nanocomposites, Appl. Surf. Sci., 2009, 256, 2826-2830. 21. K. SeokKim, K.Y. Rhee, S. JinPark, Influence of multi-walled carbon nanotubes on
1301-1306.
EP
electrochemical performance of transparent graphene electrodes, Mater. Res. Bull., 2011, 46,
AC C
22. D. Zhang, X. Zhang, Y. Chen, P. Yu, C. Wang, Y. Ma, Enhanced capacitance and rate capability of graphene/polypyrrole composite as Electrode material for supercapacitors, J. Power Sources, 2011, 196, 5990-5996. 23. C. Harish, V. Sreeharsha, C. Santhosh, R. Ramachandran, M. Saranya, T.M. Vanchinathan, K. Govardhan, A.N. Grace, Synthesis of Polyaniline/Graphene Nanocomposites and Its Optical, Electrical and Electrochemical Properties, Adv. Sci. Eng. Med., 2013, 5, 140-148.
ACCEPTED MANUSCRIPT
24. D. Kalpana, K.S. Omkumar, S. SureshKumar, N.G. Renganathan, A novel high power symmetric ZnO/carbon aerogel composite electrode for electrochemical supercapacitor, Electrochim. Acta., 2006, 52, 1309-1316.
RI PT
25. L.S. Aravinda, K.K. Nagaraja, Nagaraja, K. UdayaBhat, B.R. Bhat, ZnO/carbon nanotube nanocomposite for high energy density supercapacitors, Electrochim. Acta., 2013, 95, 119-125. 26. M. Selvakumar, D. KrishnaBhat, A. ManishAggarwal, S. PrahladhIyer, G. Sravani, Nano
SC
ZnO-activated carbon composite electrodes for supercapacitors, Physica B., 2010, 405, 22862289.
M AN U
27. T. Lu, Y. Zhang, H. Li, L. Pan, Y. Li, Z. Sun, Electrochemical behaviors of graphene–ZnO and graphene–SnO2 composite films for supercapacitor, Electrochim. Acta. 2010, 55, 4170-4173. 28. G.S. Gund, D.P. Dubal, B.H. Patil, S.S. Shinde, C.D. Lokhande, Enhanced activity of chemically synthesized hybrid graphene oxide/Mn3O4 Composite for high performance
AC C
EP
TE D
supercapacitors, Electrochim. Acta., 2013, 92, 205-215.
ACCEPTED MANUSCRIPT [SC] (F/g) 25 59
Activated graphene/ZnO Graphene/ZnO
84
Graphene/ZnO
[SR] (mV/s) 10
[EL]
[R]
6M KOH
30
5
0.1M TBAPC/DMF
31
-
6M KOH
32
61.7
50
1M KCl
16
122.4
5
6M KOH
Active material coated on Ni foam electrode Two symmetric electrodes separated by thin polypropylene separator Active material coated on stainless steel electrode ZnO deposited on graphene by USP method Active material coated on carbon paper electrode [R] Reference
M AN U
SC
This work [SC] Specific capacitance [SR] Scan Rate [EL] Electrolyte
Electrode preparation
RI PT
Electrode Material Carbon aerogel/ ZnO Functionalized CNT/ZnO
AC C
EP
TE D
Table 1: ZnO based electrode materials with specific capacitance values
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Fig 1: Schematic digram of G-ZnO nanocomposite synthesis.
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
Fig 2: XRD pattern G-ZnO composite and graphene oxide (Inset picture)
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
Fig 3: (a) DRS UV spectrum of G-ZnO composite and (b) optical band gap diagram of GZnO
Fig 4: FTIR spectrum (a) G-ZnO composite (b) Graphene Oxide
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
Fig 5: HRTEM images of G-ZnO nanocomposite at various magnifications and EDS spectrum of G-ZnO nanocomposite (Inset picture of b)
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Fig 6: Cyclic voltammetry performance (a) Graphene Oxide (b) G-ZnO composite at different scan rates
ACCEPTED MANUSCRIPT
TE D
M AN U
SC
RI PT
Fig 7: Comparison Cyclic voltammetry response of GO, rGO and G-ZnO composite at 100 mV/s scan rate.
AC C
EP
Fig 8: Plot of scan rate verse specific capacitance for GO, rGO, and G-ZnO nanocomposite
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
Fig 9: Charge/Discharge behavior of GO and G-ZnO electrodes at current density of 0.1 A/g
Fig 10: Nyquist plot and an equivalent circuit of GO (a) and G-ZnO (b).
