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A novel method to prepare metal oxide electrode: Spin-coating with thermal decomposition
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Chinese Chemical Letters 22 (2011) 354–357 www.elsevier.com/locate/cclet
A novel method to prepare metal oxide electrode: Spin-coating with thermal decomposition Hao Xu, Wei Yan *, Cheng Li Tang Department of Environmental Science and Technology, Xi’an Jiaotong University, Xi’an 710049, China Received 9 July 2010 Available online 19 December 2010
Abstract In this work, we propose a new spin-coating method coupling with high thermal decomposition, to prepare the tin-antimony (Sn– Sb) oxide electrode. The character of the spin-coating electrode was compared with the dip-coating electrode through X-ray diffraction (XRD), scanning electron microscopy (SEM), accelerated life test, cyclic voltammetry, and electrolytic degradability. The results showed that the spin-coating electrode had a better defined crystal form, a smoother and more compact surface than that of the dip-coating electrode. Service time of the spin-coating electrode was determined to be longer than 15 h, and it was less than 2 min for the dip-coating electrode. Electrochemical characterization analysis showed that the electrolytic degradability of the spincoating electrode is better than that of the dip-coating electrode. # 2010 Wei Yan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Spin-coating; Dip-coating; Thermal decomposition; Electro properties
In the past 20 years there has been lots of interest in the elimination of pollutants by electrochemical methods, such as direct oxidation on electrode surface, indirect oxidation [1] and electro-Fenton reactions through hydroxyl radicals [2]. In these methods, the key part is the anode used. Metal oxide anodes, which usually consist of a titanium substrate covered with metallic oxide films, are the most widely used type, e.g. Ti/PbO2 [3], Ti/SnO2–Sb2O5 [4], Ti/RuO2 [5], and Ti/IrO2 [6]. At present, the methods used for anode preparation include thermal decomposition [7], electrodeposition [4], spray pyrolysis [8], sol–gel process [9], sputtering [10], chemical vapor deposition [11], and electron beam evaporation [12]. Thermal decomposition is the most common and the easiest method to prepare metallic oxide electrodes. However, the precursor mixture of metallic oxide cannot distribute symmetrically on the substrate which may probably affect the electrochemical performance of the anodes. Thus, it is necessary to find a new method to solve this unsymmetrical distribution problem. The spin-coating method [13] is a simple method for preparing films from solution. As far as we know, there are few reports on using the spin-coating method to prepare electrodes. In this work, we established a new method, using spincoating followed with thermal decomposition, to prepare the metal oxide anode sticks. The as-prepared electrode was used to compare with the dip-coating electrode by means of the instrument analysis (e.g. SEM, XRD and cyclic voltammetry) in order to find out which one was better.
* Corresponding author. E-mail address: [email protected] (W. Yan). 1001-8417/$ – see front matter # 2010 Wei Yan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2010.10.027
H. Xu et al. / Chinese Chemical Letters 22 (2011) 354–357
355
1. Experimental Titanium metal sticks of 150 mm in length and a diameter of 10 mm were obtained commercially and were mechanically polished with 600-grid sand papers, rinsed with distilled water. Then, the sticks were immersed into a mixture of acetone and 1 mol L 1 NaOH (1:1, v/v) in an ultrasonic cleaner for removing organic compounds on the surface, etched in 10 wt% oxalic acid at 98 8C for 2 h, and then washed with distilled water. The precursor solution was prepared by dissolving 10 wt% SnCl46H2O and 1 wt% SbCl3 in a solution consisting of 10 mL n-butanol, 10 mL isopropanol, 10 mL ethanol and 2 mL hydrochloric acid (37%). The dip-coating preparation process was carried out followed by the literature [4,14,15]. The spin-coating preparation process was carried out on a proprietary equipment and procedure [16]. The titanium stick was clipped by the clamp, and then brushed with the precursor solution. Under the set temperature (120 8C), the stick was rotating at a speed of 1500 rpm for 15 min to allow the solvents to vaporize, and then it was calcined in an oven at 450 8C for 15 min. This procedure was repeated 10 times. Finally, the anode was annealed at 450 8C for 1 h. The structure of the as-prepared anodes was characterized by a Rigaku D/MAX-2400X X-Ray Diffractometer with CuKa radiation. The morphology of the metal oxide coating film was examined by SEM (JEOL, JSM-6390A). The electrochemical characters of the anode were performed in a three-electrode cell at room temperature in 1 mol L 1 H2SO4. The as-prepared electrodes were served as the working electrodes. The counter electrode was a copper plate, and an Ag/ AgCl/saturated KCl electrode was used as the reference electrode. The electrochemical measurement was made with an electrochemical system (LK3200A, Lanlike, China). The cyclic voltammetry was carried out at a scan speed of 50 mV s 1. During the accelerated life test, the current density was 100 mA cm 2. We used the as-prepared electrodes as the anodes and stainless steel as the cathode. The electrolysis experiment was carried out to dispose 450 mL 300 mg L 1 phenol with a current density of 5 mA cm 2. The COD value of the solution was examined by a COD tester (LianHua 5B-3C, China). 2. Results and discussion Fig. 1 shows the XRD pattern of the as-synthesized Sn–Sb oxide anode electrode prepared by dip-coating and spincoating coupling with the thermal decomposition method. The peaks at 26.78, 348, 51.98 are the characteristic peaks of the rutile SnO2 [17], indicating that Sn–Sb oxide film is formed on the Ti substrate surface. Compared with SnO2 prepared by the dip-coating method, the reflection intensity of SnO2 prepared by spin-coating method increased and the half-widths of the reflection peaks decreased, as shown in Fig. 1, which suggests better and larger crystals of SnO2 obtained from the spin-coating method. The Ti peaks were also present because the powder sample used for X-ray diffraction was scraped from the electrode mechanically, which allowed some Ti to transfer to the powder sample inadvertently. Fig. 2 shows the SEM images of the as-synthesized Sn–Sb electrodes prepared by dip-coating and spin-coating coupling with the thermal decomposition method. From earlier reports [4], we know that the Sb-doped SnO2 electrode prepared by the thermal decomposition method exhibited a typical cracked-mud structure, which would facilitate the electrolyte’s diffusion to the Ti substrate and accelerate the formation of TiO2 with poor conductivity and subsequent [()TD$FIG] 1400
dip-coating spin-coating
Ti Rutile (110)
1200
Rutile (101)
Ti Rutile (211)
Intensity
1000
Ti
800 600 400 200 0 20
30
40
50
60
70
80
2Theta / degree Fig. 1. XRD patterns of the as-prepared Sn–Sb electrodes by different methods.
[()TD$FIG] 356
5.5
Potential / (V vs Ag/AgCl)
Fig. 2. SEM images of the Ti/SnO2–Sb anode by different methods: (a) spin-coating; (b) dip-coating.
Potential / (V vs Ag/AgCl)
[()TD$FIG]
H. Xu et al. / Chinese Chemical Letters 22 (2011) 354–357
a
5.0 4.5 4.0 3.5
5.5
b
5.0 4.5 4.0 3.5 3.0
3.0 0
5
10
15
0
20
40
Time / h
60
80
100
Time / s
Fig. 3. Potential variation with time in accelerated life tests performed in 1 mol L (b) dip-coating electrode.
1
H2SO4 solution under 100 mA cm 2: (a) spin-coating electrode;
falling of Sb-doped SnO2 film. In Fig. 2a, the surface of the spin-coating electrode was much smoother and more compact than the dip-coating electrode (Fig. 2b). This may result in a longer accelerated life span of the spin-coating electrode than the dip-coating electrode. Fig. 3 shows the potential change with time in the accelerated life tests for two different electrodes. There was a long steady period (more than 10 h) for the spin-coating electrode (Fig. 3a). The dip-coating electrode demonstrated a sharp increase in potential (Fig. 3b). It was observed that the survival time (using 6.0 Vas the judging standard) of the spin-coating electrode was more than 15 h (Fig. 3a), but it was less than 2 min for the dip-coating electrode (Fig. 3b) which was consistent with the results showed in earlier reports [4,14]. Fig. 4 shows the cyclic voltammetry curves of the two kinds of electrodes. The Sn–Sb oxide anode prepared by spin-coating method exhibits a high oxygen evolution potential, i.e. the oxygen evolution potential is 2.01 V at 2 2 [()TD$FIG]1 mA cm , which is higher than the dip-coating one of 1.66 V at 1 mA cm . Therefore, the spin-coating electrode
Current density / mA cm
-2
140 120 100 80 60 dip-coating method spin-coating method
40 20 0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Potential / (V vs Ag/AgCl) Fig. 4. The cyclic voltammetry curves of the as-prepared Sn–Sb oxide anode by dip-coating and spin-coating methods in 1 mol L
1
H2SO4.
[()TD$FIG]
H. Xu et al. / Chinese Chemical Letters 22 (2011) 354–357
357
580
Solution COD / mgL
-1
560 540 520 500 480 460
dip-coating method spin-coating method
440 420 0
20
40
60
80
100
Time / h Fig. 5. The electrochemical degradation curves of two kinds of electrodes in 300 mg L
1
phenol solution.
can have a better performance in the electrochemical degradation of the organic contaminants in wastewater. Fig. 5 shows the electrochemical degradation curves of these two types of electrode, and the spin-coating electrode had higher degradation efficiency. The COD removal efficiency for the spin-coating electrode was 26% at 90 min, which was only 8.4% for the dip-coating electrode at the same time. 3. Conclusions We have prepared the Sn–Sb oxide anode with a spin-coating method followed by thermal decomposition. The XRD pattern indicated that the Sn–Sb oxide film prepared by a spin-coating method have a better defined crystal form than the film prepared by dip-coating method. The SEM images showed that the electrode surface prepared by spincoating method is much smoother and more compact than that prepared by dip-coating method. The test results mentioned above illustrate the spin-coating electrodes have better performance than the dip-coating electrodes in the accelerated life test. The spin-coating electrode has a higher oxygen evolution potential, which leads to a higher COD removal efficiency during the degradation of phenol wastewater. The point we have to make is that the spin-coating method is only suitable for the preparation of cylindrical electrodes. Acknowledgments The authors gratefully acknowledge the financial support from the Program for New Century Excellent Talents in University (No. NCET-07-0683), and President Research Fund of Xi’an Jiaotong University (No. 08140016). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
A. Carlos, H. Martinez, F. Sergio, Chem. Soc. Rev. 35 (2006) 1324. C.C. Jiang, J.F. Zhang, J. Zhejiang Univ. Sci. A 8 (2007) 1118. A.B. Velichenko, D.V. Girenko, F.I. Danilov, J. Electroanal. Chem. 405 (1996) 127. H.Y. Ding, Y.J. Feng, J.F. Liu, Mater. Lett. 61 (2007) 4920. Y.H. Cui, X.Y. Li, G.H. Chen, Wat. Res. 43 (2009) 1968. J.M. Hu, J.Q. Zhang, H.M. Meng, Electrochim. Acta 50 (2005) 5370. A.S. Huang, G.H. Zhao, H.X. Li, Chin. Chem. Lett. 18 (2007) 997. L.B. Correa, C. Comninellis, A. Battisti, J. Appl. Electrochem. 27 (1997) 970. J. Grimm, D. Bessarabov, W. Maier, Desalination 115 (1998) 295. N.Y. Shishkin, I.M. Zharsky, V.G. Lugin, Sens. Actuat. B 48 (1998) 403. S.C. Ray, M.K. Karanjai, D. Dasgupta, Thin Solid Films 307 (1997) 221. M. Yaowu, O. Yuzo, N. Takehito, Thin Solid Films 416 (2002) 248. H. Bai, G.Q. Shi, Sensors 7 (2007) 267. X.M. Chen, F.R. Gao, G.H. Chen, J. Appl. Electrochem. 35 (2005) 185. X.Y. Li, Y.H. Cui, Y.J. Feng, et al. Wat. Res. 39 (2005) 1972. W. Yan, H. Xu, C.L. Tang, Chinese Patent 200920245296.8. X.M. Chen, G.H. Chen, Electrochim. Acta 50 (2005) 4155.
Chinese Chemical Letters 22 (2011) 354–357 www.elsevier.com/locate/cclet
A novel method to prepare metal oxide electrode: Spin-coating with thermal decomposition Hao Xu, Wei Yan *, Cheng Li Tang Department of Environmental Science and Technology, Xi’an Jiaotong University, Xi’an 710049, China Received 9 July 2010 Available online 19 December 2010
Abstract In this work, we propose a new spin-coating method coupling with high thermal decomposition, to prepare the tin-antimony (Sn– Sb) oxide electrode. The character of the spin-coating electrode was compared with the dip-coating electrode through X-ray diffraction (XRD), scanning electron microscopy (SEM), accelerated life test, cyclic voltammetry, and electrolytic degradability. The results showed that the spin-coating electrode had a better defined crystal form, a smoother and more compact surface than that of the dip-coating electrode. Service time of the spin-coating electrode was determined to be longer than 15 h, and it was less than 2 min for the dip-coating electrode. Electrochemical characterization analysis showed that the electrolytic degradability of the spincoating electrode is better than that of the dip-coating electrode. # 2010 Wei Yan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Spin-coating; Dip-coating; Thermal decomposition; Electro properties
In the past 20 years there has been lots of interest in the elimination of pollutants by electrochemical methods, such as direct oxidation on electrode surface, indirect oxidation [1] and electro-Fenton reactions through hydroxyl radicals [2]. In these methods, the key part is the anode used. Metal oxide anodes, which usually consist of a titanium substrate covered with metallic oxide films, are the most widely used type, e.g. Ti/PbO2 [3], Ti/SnO2–Sb2O5 [4], Ti/RuO2 [5], and Ti/IrO2 [6]. At present, the methods used for anode preparation include thermal decomposition [7], electrodeposition [4], spray pyrolysis [8], sol–gel process [9], sputtering [10], chemical vapor deposition [11], and electron beam evaporation [12]. Thermal decomposition is the most common and the easiest method to prepare metallic oxide electrodes. However, the precursor mixture of metallic oxide cannot distribute symmetrically on the substrate which may probably affect the electrochemical performance of the anodes. Thus, it is necessary to find a new method to solve this unsymmetrical distribution problem. The spin-coating method [13] is a simple method for preparing films from solution. As far as we know, there are few reports on using the spin-coating method to prepare electrodes. In this work, we established a new method, using spincoating followed with thermal decomposition, to prepare the metal oxide anode sticks. The as-prepared electrode was used to compare with the dip-coating electrode by means of the instrument analysis (e.g. SEM, XRD and cyclic voltammetry) in order to find out which one was better.
* Corresponding author. E-mail address: [email protected] (W. Yan). 1001-8417/$ – see front matter # 2010 Wei Yan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2010.10.027
H. Xu et al. / Chinese Chemical Letters 22 (2011) 354–357
355
1. Experimental Titanium metal sticks of 150 mm in length and a diameter of 10 mm were obtained commercially and were mechanically polished with 600-grid sand papers, rinsed with distilled water. Then, the sticks were immersed into a mixture of acetone and 1 mol L 1 NaOH (1:1, v/v) in an ultrasonic cleaner for removing organic compounds on the surface, etched in 10 wt% oxalic acid at 98 8C for 2 h, and then washed with distilled water. The precursor solution was prepared by dissolving 10 wt% SnCl46H2O and 1 wt% SbCl3 in a solution consisting of 10 mL n-butanol, 10 mL isopropanol, 10 mL ethanol and 2 mL hydrochloric acid (37%). The dip-coating preparation process was carried out followed by the literature [4,14,15]. The spin-coating preparation process was carried out on a proprietary equipment and procedure [16]. The titanium stick was clipped by the clamp, and then brushed with the precursor solution. Under the set temperature (120 8C), the stick was rotating at a speed of 1500 rpm for 15 min to allow the solvents to vaporize, and then it was calcined in an oven at 450 8C for 15 min. This procedure was repeated 10 times. Finally, the anode was annealed at 450 8C for 1 h. The structure of the as-prepared anodes was characterized by a Rigaku D/MAX-2400X X-Ray Diffractometer with CuKa radiation. The morphology of the metal oxide coating film was examined by SEM (JEOL, JSM-6390A). The electrochemical characters of the anode were performed in a three-electrode cell at room temperature in 1 mol L 1 H2SO4. The as-prepared electrodes were served as the working electrodes. The counter electrode was a copper plate, and an Ag/ AgCl/saturated KCl electrode was used as the reference electrode. The electrochemical measurement was made with an electrochemical system (LK3200A, Lanlike, China). The cyclic voltammetry was carried out at a scan speed of 50 mV s 1. During the accelerated life test, the current density was 100 mA cm 2. We used the as-prepared electrodes as the anodes and stainless steel as the cathode. The electrolysis experiment was carried out to dispose 450 mL 300 mg L 1 phenol with a current density of 5 mA cm 2. The COD value of the solution was examined by a COD tester (LianHua 5B-3C, China). 2. Results and discussion Fig. 1 shows the XRD pattern of the as-synthesized Sn–Sb oxide anode electrode prepared by dip-coating and spincoating coupling with the thermal decomposition method. The peaks at 26.78, 348, 51.98 are the characteristic peaks of the rutile SnO2 [17], indicating that Sn–Sb oxide film is formed on the Ti substrate surface. Compared with SnO2 prepared by the dip-coating method, the reflection intensity of SnO2 prepared by spin-coating method increased and the half-widths of the reflection peaks decreased, as shown in Fig. 1, which suggests better and larger crystals of SnO2 obtained from the spin-coating method. The Ti peaks were also present because the powder sample used for X-ray diffraction was scraped from the electrode mechanically, which allowed some Ti to transfer to the powder sample inadvertently. Fig. 2 shows the SEM images of the as-synthesized Sn–Sb electrodes prepared by dip-coating and spin-coating coupling with the thermal decomposition method. From earlier reports [4], we know that the Sb-doped SnO2 electrode prepared by the thermal decomposition method exhibited a typical cracked-mud structure, which would facilitate the electrolyte’s diffusion to the Ti substrate and accelerate the formation of TiO2 with poor conductivity and subsequent [()TD$FIG] 1400
dip-coating spin-coating
Ti Rutile (110)
1200
Rutile (101)
Ti Rutile (211)
Intensity
1000
Ti
800 600 400 200 0 20
30
40
50
60
70
80
2Theta / degree Fig. 1. XRD patterns of the as-prepared Sn–Sb electrodes by different methods.
[()TD$FIG] 356
5.5
Potential / (V vs Ag/AgCl)
Fig. 2. SEM images of the Ti/SnO2–Sb anode by different methods: (a) spin-coating; (b) dip-coating.
Potential / (V vs Ag/AgCl)
[()TD$FIG]
H. Xu et al. / Chinese Chemical Letters 22 (2011) 354–357
a
5.0 4.5 4.0 3.5
5.5
b
5.0 4.5 4.0 3.5 3.0
3.0 0
5
10
15
0
20
40
Time / h
60
80
100
Time / s
Fig. 3. Potential variation with time in accelerated life tests performed in 1 mol L (b) dip-coating electrode.
1
H2SO4 solution under 100 mA cm 2: (a) spin-coating electrode;
falling of Sb-doped SnO2 film. In Fig. 2a, the surface of the spin-coating electrode was much smoother and more compact than the dip-coating electrode (Fig. 2b). This may result in a longer accelerated life span of the spin-coating electrode than the dip-coating electrode. Fig. 3 shows the potential change with time in the accelerated life tests for two different electrodes. There was a long steady period (more than 10 h) for the spin-coating electrode (Fig. 3a). The dip-coating electrode demonstrated a sharp increase in potential (Fig. 3b). It was observed that the survival time (using 6.0 Vas the judging standard) of the spin-coating electrode was more than 15 h (Fig. 3a), but it was less than 2 min for the dip-coating electrode (Fig. 3b) which was consistent with the results showed in earlier reports [4,14]. Fig. 4 shows the cyclic voltammetry curves of the two kinds of electrodes. The Sn–Sb oxide anode prepared by spin-coating method exhibits a high oxygen evolution potential, i.e. the oxygen evolution potential is 2.01 V at 2 2 [()TD$FIG]1 mA cm , which is higher than the dip-coating one of 1.66 V at 1 mA cm . Therefore, the spin-coating electrode
Current density / mA cm
-2
140 120 100 80 60 dip-coating method spin-coating method
40 20 0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Potential / (V vs Ag/AgCl) Fig. 4. The cyclic voltammetry curves of the as-prepared Sn–Sb oxide anode by dip-coating and spin-coating methods in 1 mol L
1
H2SO4.
[()TD$FIG]
H. Xu et al. / Chinese Chemical Letters 22 (2011) 354–357
357
580
Solution COD / mgL
-1
560 540 520 500 480 460
dip-coating method spin-coating method
440 420 0
20
40
60
80
100
Time / h Fig. 5. The electrochemical degradation curves of two kinds of electrodes in 300 mg L
1
phenol solution.
can have a better performance in the electrochemical degradation of the organic contaminants in wastewater. Fig. 5 shows the electrochemical degradation curves of these two types of electrode, and the spin-coating electrode had higher degradation efficiency. The COD removal efficiency for the spin-coating electrode was 26% at 90 min, which was only 8.4% for the dip-coating electrode at the same time. 3. Conclusions We have prepared the Sn–Sb oxide anode with a spin-coating method followed by thermal decomposition. The XRD pattern indicated that the Sn–Sb oxide film prepared by a spin-coating method have a better defined crystal form than the film prepared by dip-coating method. The SEM images showed that the electrode surface prepared by spincoating method is much smoother and more compact than that prepared by dip-coating method. The test results mentioned above illustrate the spin-coating electrodes have better performance than the dip-coating electrodes in the accelerated life test. The spin-coating electrode has a higher oxygen evolution potential, which leads to a higher COD removal efficiency during the degradation of phenol wastewater. The point we have to make is that the spin-coating method is only suitable for the preparation of cylindrical electrodes. Acknowledgments The authors gratefully acknowledge the financial support from the Program for New Century Excellent Talents in University (No. NCET-07-0683), and President Research Fund of Xi’an Jiaotong University (No. 08140016). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
A. Carlos, H. Martinez, F. Sergio, Chem. Soc. Rev. 35 (2006) 1324. C.C. Jiang, J.F. Zhang, J. Zhejiang Univ. Sci. A 8 (2007) 1118. A.B. Velichenko, D.V. Girenko, F.I. Danilov, J. Electroanal. Chem. 405 (1996) 127. H.Y. Ding, Y.J. Feng, J.F. Liu, Mater. Lett. 61 (2007) 4920. Y.H. Cui, X.Y. Li, G.H. Chen, Wat. Res. 43 (2009) 1968. J.M. Hu, J.Q. Zhang, H.M. Meng, Electrochim. Acta 50 (2005) 5370. A.S. Huang, G.H. Zhao, H.X. Li, Chin. Chem. Lett. 18 (2007) 997. L.B. Correa, C. Comninellis, A. Battisti, J. Appl. Electrochem. 27 (1997) 970. J. Grimm, D. Bessarabov, W. Maier, Desalination 115 (1998) 295. N.Y. Shishkin, I.M. Zharsky, V.G. Lugin, Sens. Actuat. B 48 (1998) 403. S.C. Ray, M.K. Karanjai, D. Dasgupta, Thin Solid Films 307 (1997) 221. M. Yaowu, O. Yuzo, N. Takehito, Thin Solid Films 416 (2002) 248. H. Bai, G.Q. Shi, Sensors 7 (2007) 267. X.M. Chen, F.R. Gao, G.H. Chen, J. Appl. Electrochem. 35 (2005) 185. X.Y. Li, Y.H. Cui, Y.J. Feng, et al. Wat. Res. 39 (2005) 1972. W. Yan, H. Xu, C.L. Tang, Chinese Patent 200920245296.8. X.M. Chen, G.H. Chen, Electrochim. Acta 50 (2005) 4155.