Preparation and electrochemical characterization of NiO nanostructure-carbon nanowall composites grown on carbon cloth

Applied Surface Science 258 (2012) 8599–8602

Contents lists available at SciVerse ScienceDirect

Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc

Preparation and electrochemical characterization of NiO nanostructure-carbon nanowall composites grown on carbon cloth Hsuan-Chen Chang a , Hsin-Yueh Chang a , Wei-Jhih Su a , Kuei-Yi Lee a,b,∗ , Wen-Ching Shih c a b c

Department of Electronic Engineering, National Taiwan University of Science and Technology, No. 43, Sec. 4, Keelung Road, Taipei 106, Taiwan Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, No. 43, Sec. 4, Keelung Road, Taipei 106, Taiwan Graduate Institute of Electro-Optical Engineering, Tatung University, No. 40, Sec. 3, Chungshan North Road, Taipei 104, Taiwan

a r t i c l e

i n f o

Article history: Received 2 August 2011 Received in revised form 10 April 2012 Accepted 12 May 2012 Available online 1 June 2012 Keywords: NiO Carbon nanowall Thermal chemical vapor deposition Plasma enhance chemical vapor deposition Electric double layer capacitor Scanning electron microscopy

a b s t r a c t This study provided a simple method to form NiO nanostructures onto the carbon nanowalls (CNWs) surface to enhance the performance of electric double layer capacitor (EDLC) characteristics. The CNWs were synthesized on carbon cloth by rf magnetron sputtering without any catalyst. Ni film was then deposited on the synthesized CNWs by e-beam evaporator. Subsequently, the vacuum annealing process and oxygen plasma treatment were used to form the NiO nanostructures. The crystallize structures of NiO nanostructures and CNWs were examined by Raman scattering spectroscopy. To realize the electrochemical properties of NiO/CNWs/carbon cloth composite, cyclic voltammetry (CV) and galvanostatic charge–discharge tests were investigated. Due to the relatively larger surface area of CNWs and the quickly reversible redox reaction and pseudo-capacitive properties of NiO nanostructures, the measured results demonstrated that the NiO/CNWs/carbon cloth is a suitable electrode material for EDLC applications. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Electric double layer capacitor (EDLC) is one type of energy storage devices which has the characteristics of high power density, stable charge–discharge property, quickly current response detection, sustainability, long life span, and non-pollution in the environment [1]. EDLC is a major green resource in the 21st century. Since the EDLC stores electrical charges at the interfaces between electrode and electrolyte, the surface area of the electrode material is an important influence which concerns the capacitance of the EDLC. Some carbon-related materials such as activated carbon [2], carbon nanotube [3], and carbon nanowall (CNW) [4] are considered as the ideal electrode materials owing to their high electrical conductivity, chemical stability, structural stability and relatively larger surface area. These carbon-related materials can store more energy to promote the capacitance performances of EDLCs [2]. Among them, CNW exhibits a two-dimensional petal shaped nanostructure and can grow vertically aligned to a substrate which is believed to be one of the suitable electrode materials for EDLC applications.

∗ Corresponding author at: Department of Electronic Engineering, National Taiwan University of Science and Technology, No. 43, Sec. 4, Keelung Road, Taipei 106, Taiwan. Tel.: +886 2 2730 1254; fax: +886 2 2737 6424. E-mail address: [email protected] (K.-Y. Lee). 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.05.057

To enhance the EDLC performance, the pseudocapacitive characteristic was regularly used for improving the EDLC capacitance. The pseudocapacitive process consists of faradic redox reactions which occur within the transitional metal-oxides, such as RuO2 [5–7], IrO2 [8,9], MnOX [10], and NiO [11,12]. Among these materials, RuO2 has been researched mostly, which exhibits an excellent property in capacitor applications, but high cost limits the development of RuO2 . NiO has several oxidation numbers that have quickly reversible redox reaction at the electrode surface. The electronic transmission in NiO could be more efficient to enhance the capacitive current response [12]. Moreover, relative to the other metal-oxides, NiO is more abundant and cheap which can widely use in industrial purposes. NiO as a EDLC electrode material can be prepared by several methods, for example, liquid crystal templating electrodeposition [13], simple liquid-phase process [14], thermal treatment of an electrodeposition [15], and sol–gel prepared nickel hydroxide [16,17]. However, some synthesized NiO grown by these methods may have some disadvantages, like unstable fabrication, non-uniform deposition, and worse crystallinity. The results maybe influence the efficiency of EDLC. In this work, the CNWs were grown on the carbon cloth by rf magnetron sputtering. The combination of CNWs and carbon cloth exhibited a high adhesion in electrolyte which avoids the exfoliation during the EDLC measurements. Subsequently, the Ni film was deposited on the CNWs. The vacuum annealing process and oxygen plasma treatment were used to form the NiO

8600

H.-C. Chang et al. / Applied Surface Science 258 (2012) 8599–8602

nanostructures onto the CNWs surface uniformly. It is demonstrated that the NiO/CNWs/carbon cloth formed by the study was a suitable electrode material for EDLC applications. This method provided a simple approach for NiO/CNWs electrode synthesis. 2. Experimental procedure Carbon cloth was split into pieces with size of 10 mm × 10 mm as the substrate. The CNWs nanostructures were deposited on the double-surface of carbon cloth by using rf magnetron sputtering system, which was performed in a reactive chamber with a 3-inchcarbon target, and the distance between target and substrate was 45 mm. The flowing rates of Ar and H2 were 5 and 3 sccm, respectively. The temperature of substrate was heated to 350 ◦ C for 1 h and the depositing time of CNWs was 40 min with a rf power of 200 W at a working pressure of 7.5 × 10−3 Torr. After the CNWs nanostructures depositing on the carbon cloth, the Ni film was deposited onto the synthesized CNWs surface by e-beam evaporator. The thickness of Ni film was 20 nm. Subsequently, the deposited Ni film was annealed at 750 ◦ C at a pressure of 4 Torr to form the Ni nanoparticles on the CNWs surface. To form the NiO nanostructures on the CNWs surface, we used oxygen plasma to treat Ni nanostructures with an rf power of 25 W at a pressure of 4.0 × 10−1 Torr for 30 min. The surface and structure details of NiO/CNWs/carbon cloth composite were analyzed by scanning electron microscopy. The crystallize structures of NiO nanostructures and CNWs were examined by Raman scattering spectroscopy with a 514.5 nm excitation line of Ar ion laser. To provide a clear understanding of the electrochemical properties of NiO/CNWs/carbon cloth composite, cyclic voltammetry (CV) and galvanostatic charge–discharge tests were investigated by a three-electrode mode (counter electrode, reference electrode and working electrode) system. The supporting electrolyte was 0.1 M KOH solution. In the CV curves measurement, the working electrode was cycled five times at a rate of 50 mV/s, and the charge–discharge characteristics were measured for 100 cycles. 3. Results and discussion Fig. 1(a) shows the carbon cloth which image of carbon fibers with a diameter of about 10 ␮m. Fig. 1(b) shows the morphological features of CNWs/carbon cloth. The free-standing and vertically matted CNWs were fabricated by rf magnetron sputtering system without any catalyst. According to the inset of Fig. 1(b), the thickness and length of CNWs were about 5–10 nm and 300 nm, respectively. The synthesized CNWs on the carbon cloth surface presented high number-density, high directly aspect and large surface area. Fig. 1(c) indicates that the NiO nanostructures were uniformly covered on the surface of CNWs. The inset of Fig. 1(c) shows the morphology of NiO presented granular structure with a diameter of about 20 nm. Typical Raman spectrum for CNW was found a strong peak at 1586 cm−1 (G band), which indicated the fabrication of graphite with a sp2 -C bonding structure [18,19]. The G band is associated with the doubly degenerated in-plane transverse (iTO) and in-plane longitudinal optic (iLO) phonon modes (E2g symmetry) at the brillouin zone center, which comes form the first-order Raman scattering process [20]. Another peak at 1352 cm−1 (D band) is conformed with the disorder structure relative to G band in graphite structure [21]. The D band involves one iTO phonon and one defect near the K-point, which comes from the second-order Raman scattering process [22]. Fig. 2 shows the peak at 1352 cm−1 of CNWs/carbon cloth is stronger than 1586 cm−1 . Due to the oxygen plasma treatment could decrease the defects of graphite [23], the peak at 1352 cm−1 is less than 1586 cm−1 after NiO was coated on CNWs. The Raman spectrum of NiO/CNWs/carbon cloth shows

Fig. 1. SEM images of (a) carbon cloth, (b) CNWs depositing on carbon cloth, and (c) NiO synthesized on CNWs.

that the peak of NiO corresponds to one-phonon (TO and LO modes) excitation at 570 cm−1 , which confirms that the NiO nanostructures were coated on CNWs [24]. Fig. 3 presents the CV curves of carbon cloth, CNWs/carbon cloth, NiO/CNWs/carbon cloth, plotting the response current versus potential at the sweep rate of 50 mV/s. The CV curve shows that there is almost no capacitor characteristic of carbon cloth because the surface of carbon cloth is smooth and non-porous, resulting in the electrolyte hardly infiltrated into the internal surface. The CNWs have high surface area and present a flake shape on structure, increasing the reactive surface between electrode and electrolyte. Besides, it is known that the NiO possesses certain properties such as high electrochemical stability and quickly reversible redox reaction at the electrode surface [25]. The electronic transmission could be more efficient to enhance the capacitive current response.

H.-C. Chang et al. / Applied Surface Science 258 (2012) 8599–8602

8601

100

Carbon cloth CNWs/carbon cloth NiO/CNWs/carbon cloth

90 70

0.4

60 Voltage (V)

-1

Capacitance (Fg )

80

50 40 30

NiO/CNWs/carbon cloth

0.2 0.0 -0.2 4900

20

4950

5000

5050

5100

Time (s)

10 0 0

10

20

30

40

50

60

70

80

90 100 110

Cycle number Fig. 4. Variation in the capacitance values of NiO/CNWs/carbon cloth, CNWs/carbon cloth, and carbon cloth with respect to the number of charge–discharge cycles, with an inset showing galvanostatic charge–discharge curves of NiO/CNWs/carbon cloth at 0.1 mA.

Fig. 2. Raman spectra of the NiO/CNWs/carbon cloth and CNWs/carbon cloth.

Therefore, the response current of NiO/CNWs/carbon cloth is higher than those of CNWs/carbon cloth and carbon cloth. Charge–discharge curves were measured for 100 cycles. The result of NiO/CNWs/carbon cloth was plotted in Fig. 4. The result shows that the charge–discharge property was stable, and the triangular curve presented the capacitor features. The NiO nanostructures improved the electrode conductivity, and provided the pseudocapacitance to enhance the capacitance. The larger obtained capacitance can be attributed to the NiO surface oxidation and reduction reactions of nickel ions. The redox reaction of NiO in an alkaline electrolyte can be described as follow, NiO + OH− → NiOOH + e− ,

(1)

The redox reaction of Ni2+ to Ni3+ is shown in Eq. (1), and the electron can raise the current of capacitors. This pseudocapacitance behavior could be more efficient to enhance the capacitive current response [14,17]. Besides, the nano-size electrode structure exhibit large exposed interface with the electrolyte, which can promote the electrochemical reaction rate. The combination of low resistance, improved capacitance, and high surface area of nm-size structure makes the NiO/CNWs/carbon cloth ideal for the working electrode application in EDLC. The insert of Fig. 4 shows the applied voltage range of NiO/CNWs/carbon cloth was from 0.32 to 0.014 0.012 0.010

Carbon cloth CNWs/carbon cloth NiO/CNWs/carbon cloth

it , Vm

(2)

where C (F/g) is the capacitance, i (A) is the charge current, t (s) is the elapsed time in discharge, V (V) is the potential difference, and m (g) is the mass of the active material. The active material masses of the carbon cloth, CNWs/carbon cloth and NiO/CNWs/carbon cloth are 1.6, 1.9 and 2.1 mg, respectively. After 100 cycles measurement, the value of capacitance of NiO/CNWs/carbon cloth was 71.9 F/g, which was higher than that of CNWs/carbon cloth of 13.8 F/g and that of carbon cloth of 4.8 × 10−2 F/g. Additionally, the NiO/CNWs did not exfoliate from carbon cloth after the EDLC measurements, the combination of CNWs and carbon cloth exhibited a high adhesion in the KOH electrolyte. As a result, the NiO nanostructures synthesized by the vacuum annealing process and oxygen plasma treatment could improve electronic transmission, capacitive current response and kinetics of charge transportation [25], in addition to the relatively larger surface area of CNWs, the NiO/CNWs/carbon cloth is a suitable electrode material for EDLC applications.

We have synthesized the EDLC electrode with NiO/CNWs composite on carbon cloth successfully. A simple method of NiO nanostructures formation was provided. The NiO nanostructures could be formed onto the CNWs surface uniformly by the vacuum annealing process and oxygen plasma treatment. The electrochemical measurements showed that the NiO/CNWs/carbon cloth had good electrochemical capacitive performances. The combination of NiO/CNWs and carbon cloth exhibited a high adhesion in KOH electrolyte after the EDLC measurements. The NiO/CNWs/carbon cloth synthesized by the simple approach could be demonstrated as an applicable EDLC electrode.

0.006

Current (A)

C=

4. Conclusions

0.008 0.004 0.002 0.000 -0.002 -0.004 -0.006 -0.008 -0.010

-0.6

−0.26 V and the period of charge–discharge was about 50 s. These results indicated that the NiO nanostructure could improve the charge–discharge characteristics effectively. The charge–discharge curve of NiO/CNWs/carbon cloth was still stable after 100 cycles. The capacitance was evaluated from the following equation,

-0.4

-0.2

0.0

0.2

0.4

0.6

Voltage (V) Fig. 3. The cycle voltammograms at 50 mV/s for NiO/CNWs/carbon cloth, CNWs/carbon cloth, and carbon cloth.

Acknowledgements This work was financially supported by the National Science Council of Taiwan under Contract no. NSC-99-2221-E-011-072. The

8602

H.-C. Chang et al. / Applied Surface Science 258 (2012) 8599–8602

authors would like to acknowledge Professor Ying-Sheng Huang and Professor Liang-Chiun Chao for their valuable discussions and assistance in measurements. References [1] R. Shah, X. Zhang, S. Talapatra, Nanotechnology 20 (2009) 395202. [2] S. Mitani, S.I. Lee, K. Saito, Y. Korai, I. Mochida, Electrochimica Acta 51 (2006) 5487–5493. [3] S. Wen, M. Jung, O.S. Joo, S.I. Mho, Current Applied Physics 6 (2006) 1012–1015. [4] P. Justin, G.R. Rao, International Journal of Hydrogen Energy 35 (2010) 9709–9715. [5] Z. Sun, Z. Liu, B. Han, S. Miao, J. Du, Z. Miao, Carbon 44 (2005) 888–893. [6] C.C. Liu, D.S. Tsai, D. Susanti, W.C. Yeh, Y.S. Huang, F.J. Liu, Electrochimica Acta 55 (2010) 5768–5774. [7] G.H. Deng, X. Xiao, J.H. Chen, X.B. Zeng, D.L. He, Y.F. Kuang, Carbon 43 (2005) 1566–1569. [8] M.D. Stoller, S. Park, Y. Zhu, J. An, R.S. Ruoff, Nano Letters 8 (2008) 3498–3502. [9] Y.M. Chen, C.A. Chen, Y.S. Huang, K.Y. Lee, K.K. Tiong, Journal of Alloys and Compounds 487 (2009) 659–664. [10] H.R. Byon, S.W. Lee, S. Chen, P.T. Hammond, S.H. Yang, Carbon 49 (2011) 457–467. [11] B. Tao, J. Zhang, F. Miao, S. Hui, L.J. Wan, Electrochimica Acta 55 (2010) 5258–5262.

[12] U.M. Patil, R.R. Salunkhe, K.V. Gurac, C.D. Lokhande, Applied Surface Science 255 (2008) 2603–2607. [13] P.A. Nelson, J.R. Owen, Journal of the Electrochemical Society A 150 (2003) 1313–1317. [14] F.B. Zheng, Y.K. Zhou, H.L. Li, Materials Chemistry and Physics 83 (2004) 260–264. [15] C.D. Lokhande, D.P. Dubal, O.S. Joo, Current Applied Physics 11 (2010) 255–270. [16] K.C. Liu, M.A. Anderson, Journal of the Electrochemical Society 143 (1996) 124–130. [17] V. Srinivasan, J.W. Weidner, Journal of the Electrochemical Society 144 (1997) L210–L213. [18] R. John, A. Ashokreddy, C. Vijayan, T. Pradeep, Nanotechnology 22 (2011) 165701. [19] W.C. Shih, J.M. Jeng, J.T. Lo, H.C. Chen, I.N. Lin, Japanese Journal of Applied Physics 48 (2009) 081602–0816025. [20] L.M. Malarda, D.L. Mafra, S.K. Doornb, M.A. Pimentaa, Solid State Communications 149 (2009) 1136–1139. [21] C.P. Juan, C.C. Tsai, K.H. Chen, L.C. Chen, H.C. Cheng, Japanese Journal of Applied Physics 44 (2005) 8231–8236. [22] M. Hiramaysu, K. Shiji, H. Amano, M. Hori, Applied Physics Letters 84 (2004) 4708–4710. [23] C.C. Chiu, M. Yoshimura, K. Ueda, Japanese Journal of Applied Physics 47 (2008) 1952–1995. [24] N. Mironova-Ulmane, A. Kuzmin, I. Steins, J. Grabis, I. Sildos, M. Pärs, Journal of Physics 93 (2007) 012039. [25] C.Z. Yuan, B. Gao, L.G. Su, X.G. Zhang, Solid State Ionics 178 (2008) 1859–1866.