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Effect Of Surface Treatments On Supercapacitive Performance Of SnO2-RuO2 Composite Thin Films
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Science Direct Materials Today: Proceedings 18 (2019) 2848–2858
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ICMPC-2019
Effect Of Surface Treatments On Supercapacitive Performance Of SnO2-RuO2 Composite Thin Films S.N. Pusawaleab*, Prashant S. Jadhavab a
Rajarambapu Institute of Technology, Sakharale, Maharashtra. b Shivaji University, Kolhapur , Maharashtra.
Abstract
In the present work, we have adopted a simple and inexpensive route to prepare tin oxide-ruthenium oxide (SnO2RuO2) composite thin film electrodes via a chemical approach. Further, the fabricated films are treated with different surface treatments in order to tune their morphology and see its effect on the supercapacitor properties. The surface treatments that we used are annealing in air, ultrasonic weltering in NaOH and anodization. It is observed that with air annealing the specific capacitance of the pristine electrode is decreased from 166 F/g to 12 F/g this is due to the loss of hydrous content from the electrode. The electrode then has undergone another surface treatment of ultrasonic weltering where there is change in the morphology of the electrode. The specific capacitance is decreased to 106 F/g for ultrasonically weltered electrode. The effect of anodization treatment is then studied and it is observed that with this treatment the specific capacitance of the electrode is increased to 269 F/g. The increase in the specific capacitance is attributed to the comparatively smooth morphology and improvement in the conductivity of the electrode. This shows that the supercapacitive performance of the electrode can be improved by using different kind of surface treatments. In our research anodization is found to be a good surface treatment to enhance the specific capacitance of the pristine electrode. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Thin films; Supercapacitor, Chemical Synthesis; Surface treatments.
1. Introduction Supercapacitors are in growing demand nowadays due to their wide range of applications in hybrid electric vehicles, telecommunications, particularly associated with cellular phones for a reduction of the size of the batteries 1
Corresponding author. E-mail address: [email protected]
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
2849
[1]. Various materials have been researched for their supercapacitive performance such as metal oxides, polymers, and carbon. Among these hydrous form of RuO2 has shown excellent supercapacitive performance but due to its low cost, it restricts its commercial application. In order to reduce the cost, other metal oxides such as TiO2, SnO2, and MnO2 etc. were combined with RuO2. It was observed that the performance of supercapacitor electrode is strongly depend upon the active materials involved, their reversible redox transitions between various oxidation states and morphology [2]. The morphology of the supercapacitor electrode is an important aspect, as it is well known that the porous morphology of the electrode is useful for supercapacitor application because such morphology provides higher effective surface area. The morphology and hence the supercapacitive performance of electrode can be tuned by various surface treatments. In earlier studies, specific capacitance of ruthenium oxide has been enhanced by surface treatments like annealing in air [3, 4] electrochemical anodization in aqueous media [5] and ultrasonic weltering in NaOH [6]. In the present work, tin oxide-ruthenium oxide (SnO2-RuO2) composite electrodes prepared by SILAR (Successive ionic layer adsorption and reaction) and CBD (chemical bath deposition) methods are treated by various surface treatments such as annealing in air, ultrasonic weltering in NaOH and anodization. The effect of these surface treatments on the morphology, wettability and specific capacitance of the SnO2-RuO2 composite film is studied. 2. Experimental 2.1 Preparation of SnO2-RuO2 composite films and surface treatments applied The optimized SnO2–RuO2 composite films showing maximum specific capacitance value were prepared by SILAR (SnO2: RuO2= 1:3) and CBD (15 vol%) methods as described in our earlier work [7, 8]. The deposition was taken on large area stainless steel (> 16 cm2 ) substrates. The substrate is then cut into 4 identical substrates of ~ 4 cm2 area and used for surface treatment study. For air annealing, SnO2-RuO2 composite electrode was annealed in air at 423 K for 2 h. For ultrasonic weltering, the substrate coated with SnO2-RuO2 was ultrasonically weltered in 1 M NaOH for 30 min in ultrasonic cleaner and the anodization treatment was carried out in 0.1 M H2SO4 at +1.2 V for 1.30 h using potentiostat/ Galvanostat. It was observed that the SnO2-RuO2 composite film prepared by SILAR is unstable in NaOH solution so that the ultrasonic weltering was not done for SILAR deposited SnO2-RuO2 composite film. 2.2 Characterization techniques The microstructure of the films was observed using scanning electron microscopy (JEOL, JEM-6360, Japan). Static water contact angle measurement was carried out using RameHart Instrument Co., USA equipped with CCD camera. The transmission electron micrograph was obtained by Jeol JEM-2100F unit. The electrochemical study was performed in a three-electrode configuration cell consisting of SnO2-RuO2 as a working electrode, platinum as a counter electrode and saturated calomel electrode (SCE) as a reference electrode.
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S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
3. Result 3.1 Effect of Surface Treatments on SnO2-RuO2 Composite Film Prepared by SILAR Method 3.1.1 Effect of Air Annealing The morphology of pristine and air annealed SnO2-RuO2 composite film prepared by SILAR method is shown in Fig. 1 (a, b). The pristine SnO2-RuO2 composite film surface contains porous irregular shaped agglomerated morphology, which changed to a granular and comparatively smooth surface with overgrowth of particles after air annealing. The contact angle image for pristine and air annealed SnO2-RuO2 composite film is shown in Fig. 2 (a, b). The contact angle for pristine SnO2-RuO2 composite film is 1210 changed to 130 for annealed SnO2-RuO2 composite film, which shows the hydrophobic nature of the composite film is changed to hydrophilic after air annealing. It was observed that the surfaces with high surface energy are hydrophilic. As with air annealing, there is possibility of formation of nanocrystalline structure for SnO2-RuO2 composite, the nanocrystalline surface has greater surface energy, resulting in the decrease in water contact angle [9]. The supercapacitive performance of annealed SnO2-RuO2 composite electrode is studied using cyclic voltammetry (CV) in 0.5 M H2SO4 electrolyte at 5 mV/s scan rate in the potential range of -0.2 to +0.6 V vs. SCE. The cyclic voltammogram (Fig. 3) showed that specific capacitance is decreased from 183 to 67 F/g for annealed SnO2-RuO2 composite electrode compared with pristine electrode. The loss in specific capacitance value is due to the a significant loss in the water content resulting in a more ordered structure which render a higher barrier for proton diffusion in comparison with their pristine structure [10]. Also, there may be formation of nanocrystalline structure with decrease in defects (i.e. electroactive sites), decreasing the specific capacitance of electroactive species [6].
Fig. 1: The morphology of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
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(a)- Pristine (b)- Air Annealed
1.0
-2
Current density (mA.cm )
Fig. 2: The water contact angle images of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
0.5
0.0 (a) (b)
-0.5
-0.2
0.0
0.2
0.4
0.6
Voltage (V vs.SCE)
Fig. 3: The CV curves for pristine and air annealed SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 5 mV/s between -0.2 to +0.6 V vs. SCE.
3.1.2 Effect of Anodization The effect of anodization on the morphology and wettability of SnO2-RuO2 composite film is studied. Fig. 4 (a) shows the morphology of SnO2-RuO2 composite film after anodization treatment. The spongy and porous morphology is observed for SnO2-RuO2 composite film after anodization. The water contact angle decreased to 720 compared with pristine SnO2-RuO2 composite film as observed from Fig. 4 (b). The CV curve for anodized SnO2-RuO2 composite electrode is shown in Fig. 5. From the CV curve, decrease in voltammetric current is observed for anodized SnO2-RuO2 composite electrode. The specific capacitance decreased from 183 to 106 F/g for anodized SnO2-RuO2 composite electrode compared with pristine composite electrode.
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Fig. 4: (a) The morphology and (b) water contact angle image of anodized SnO2-RuO2 composite film.
Pristine Anodized
-2
Current density (mA.cm )
1.0
0.5
0.0 (a) (b)
-0.5 -0.2
0.0
0.2
0.4
0.6
Voltage (V vs. SCE) Fig. 5: The CV curves for pristine and anodized SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 5 mV/s between -0.2 to +0.6 V vs. SCE.
The comparative study of surface treatments on the contact angle and specific capacitance value of SnO2–RuO2 composite is shown in table 1.
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
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Table 1 Effect of surface treatments on specific capacitance value of SILAR deposited SnO2-RuO2 composite electrode. Specific Capacitance (F/g) Sr. Surface treatment Sample Area Contact (cm2)
No.
Angle (0)
1
Pristine
1
121
183
2.
Air annealing (423 K, 2 h)
1
13
67
3.
Anodization (0.1M H2SO4 at +1.2 V vs.
1
72
106
SCE for 1.30 h)
3.2 Effect of Surface Treatment on SnO2-RuO2 Composite Film prepared by CBD Method 3.2.1 Effect of Air Annealing In general, hydrous ruthenium oxide annealed in the temperature region close to its crystallization temperature showed a very high specific capacitance (≥720 F/g) [3]. This has been attributed to the local structures of hydrous ruthenium oxide retaining facile transport pathways for both protons and electrons [11]. The SEM images for pristine and air annealed SnO2-RuO2 composite films are shown in Fig. 6 (a, b) and water contact angle image for pristine SnO2-RuO2 composite film prepared by CBD method are shown in Fig. 7 (a, b). The larger pits observed in case of pristine SnO2-RuO2 composite electrode is vanished in annealed electrode. There is no much difference in water contact angle of pristine and annealed SnO2–RuO2 composite electrode. The CV curve for pristine and annealed SnO2-RuO2 composite electrode in the potential range of 0 to +0.8 V vs. SCE at 20 mV/s in 0.5 M H2SO4 electrolyte is shown in Fig. 8. The current was reduced significantly for annealed composite electrode reducing its specific capacitance value from 166 to 12 F/g. The significant decrease in specific capacitance value after annealing is attributed to the loss of hydrous content from the sample [12].
Fig. 6: The morphologies of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
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2
(a)- Pristine (b)- Air Annealed
-2
Current density (mA.cm )
Fig. 7: The water contact angle images of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
1
0 (a)
-1
(b)
-2 0.0
0.2
0.4
0.6
0.8
Voltage (V vs. SCE)
Fig. 8: The CV curves for pristine and annealed SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 20 mV/s between 0 to +0.8 V vs. SCE. 3.2.2 Effect of Ultrasonic Weltering The effect of ultrasonic weltering in NaOH on SnO2-RuO2 composite electrode is studied. Fig. 9 (a, b) shows the surface morphology and water contact angle image for ultrasonically weltered SnO2-RuO2 composite electrode respectively. The bigger pits and elongated structure observed for pristine SnO2-RuO2 composite is vanished for ultrasonically weltered composite electrode with small pits distributed all over the surface. The water contact angle for ultrasonically weltered SnO2-RuO2 composite film is not much altered with slight decrease compared with pristine composite film.
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
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Fig. 10 shows the CV curves for pristine and ultrasonically weltered SnO2-RuO2 composite electrode. The specific capacitance value is decreased from 166 to 106 F/g for ultrasonically weltered SnO2-RuO2 composite electrode compared with pristine electrode. This means the ultrasonic weltering treatment is not suitable for SnO2RuO2 composite electrode as decrease in specific capacitance value was observed. Slight loss in weight of deposited film was observed after ultrasonic treatment due to the removal of unbound surface particles.
Fig. 9: (a) The morphology and (b) water contact angle image of ultrasonically weltered SnO2-RuO2 composite film.
(a)- Pristine (b)- Ultrasonic W eltered
-2
Current density (mA.cm )
2
1
0
-1
(a) (b)
-2 0.0
0.2
0.4
0.6
0.8
Voltage (V vs. SCE) Fig. 10: The CV curves for pristine and ultrasonically weltered SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 20 mV/s between 0 to +0.8 V vs. SCE.
3.2.3 Effect of Anodization The effect of anodization on SnO2-RuO2 composite electrode is studied. Fig. 11 (a, b) shows the morphology and contact angle image for SnO2-RuO2 composite electrode after anodization. The morphology of the
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S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
electrode is changed from rough with irregular pits and elongated structure to relatively smooth surface covered all over the substrate after the anodization. The hydrophilic surface of pristine SnO2-RuO2 composite electrode was changed to superhydrophilic with water contact angle ~70. The CV curve for pristine and anodized SnO2-RuO2 electrode is shown in Fig. 12. From which it is observed that there is an increase in current response for SnO2-RuO2 electrode after anodization. There is possibility of presence of some chloride precursors in pristine samples, with anodization there is formation of impurity-free SnO2-RuO2, which improves the conductivity. Also as the surface is smooth and porous the electrolyte can easily access the bulk of the electrode, which results into maximum current response. [5]. Thus, anodization method is found to be useful surface treatment for SnO2-RuO2 composite electrode prepared by CBD method.
-2
Current density (mA.cm )
Fig. 11: (a) The morphology and (b) water contact angle image of anodized SnO2-RuO2 composite Film.
3.0
(a)- Pristine (b)- Anodized
1.5 0.0 -1.5
(a) (b)
-3.0 -4.5 0.0
0.2
0.4
0.6
0.8
Voltage (V vs. SCE) Fig. 12: The CV curves for pristine and anodized SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 20 mV/s between 0 to +0.8 V vs. SCE.
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
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The comparative study of surface treatments on the contact angle and specific capacitance value of SnO2–RuO2 composite is shown in Table 2. Table 2: Effect of surface treatments on specific capacitance value of CBD deposited SnO2-RuO2 Sr.
Surface Treatment
Sample
Contact 2
No.
0
Specific
Area (cm )
Angle ( )
Capacitance (F/g)
1
Pristine
1
14
166
2.
Air annealing (423 K, 2 h)
1
13
12
3.
Ultrasonic weltering (in 1 M NaOH for 30
1
12
106
1
7
269
min) 4.
Anodization (0.1 M H2SO4 at +1.2 V vs. SCE for 1.30 h)
Conclusions The effect of surface treatments on the morphology, wettability and specific capacitance on SnO2-RuO2 composite films deposited by SILAR and CBD method is studied successfully. It is observed that the morphology of the SnO2-RuO2 composite film deposited by SILAR method changed with annealing and anodization, in addition, the hydrophobic surface of pristine composite film changed to hydrophilic. The specific capacitance value decreased for both annealed and anodized SnO2-RuO2 composite electrode deposited by SILAR method. In case of SnO2-RuO2 composite films deposited by CBD method, the surface treatments changed the morphology to relatively smooth surface. The decrease in specific capacitance is observed for annealed and ultrasonically weltered SnO2-RuO2 composite films deposited by CBD method. However, with anodization treatment, the specific capacitance of the composite electrode deposited by CBD method is increased from 166 to 269 F/g. Thus anodization is found to be useful surface treatment for this electrode. References
[1] R. Kotz, M. Carlen,Principles and applications of electrochemical capacitors, Electrochim. Acta, 2000, 45, 24832498. [2] M. Wu, L. Zhang, D. Wang, C. Xiao, S. Zhang, Cathodic deposition and characterization of tin oxide coatings on graphite for electrochemical capacitors, J. Power Sources 175 (2008) 669-674. [3] J. P. Zheng, P. J. Cygan, T. R. Jow, Hydrous Ruthenium oxide as electrode material for electrochemical capacitors, J. Electrochem. Soc. 142 (1995) 2699-2703. [4] B. O. Park, C. D. Lokhande, H. S. Park, K. D. Jung, O. S. Joo, Performance of with electrodeposited ruthenium oxide film electrode –effect of film thickness, J. Power Sources 134 (2004) 148-152. [5] C. C. Hu and C. C. Wang, Improving the utilization of ruthenium oxide within thick carbon –ruthenium oxide composites by annealing and anodizing for electrochemical capacitors, Electrochem. Commun. 4 (2002) 554559.
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[6] C. C. Wang and C. C. Hu, Electrochemical and textural characterization of binary Ru Sn oxides synthesized under mild hydrothermal conditions for supercapacitors, Electrochim. Acta, 50 (2005) 2573-2581. [7] S.N. Pusawale, P. R. Deshmukh, J. L. Gunjakar, C. D. Lokhande, SnO2-RuO2 composite films by chemical deposition for supercapacitor application, Mat. Chem. Phy. 139 (2013) 416-422. [8] S. N. Pusawale, P. R. Deshmukh, P. S. Jadhav, C. D. Lokhande, Electrochemical properties of chemically synthesized SnO2-RuO2 mixed films, Mat. Renew. Sust. Ene. 8 (2019) 1. [9] K. K. S. Lau, J. Bico, K. B. K. Teo, M. Chhowalla, G. A. J. Amaratunga, W. I. Milne, G. H. McKinley, K. K. Gleason, Superhydrophobic carbon nanotube forests, Nano Lett. 3 (2003) 1701-1705. [10] O. Barbieri, M. Hahn, A. Foelske, R. Kotz, Effect of electronic resistance and water content on the performance of RuO2 supercapacitors, J. Electrochem. Soc. 153 (2006) A2049-A2054. [11] D. A. McKeown, P. L. Hagans, L. P. L. Carette, A. E. Russell, K. E. Swider, D. R. Rolison, Structure of hydrous ruthenium oxides: Implications for charge storage, J. Phys. Chem. B 103 (1999) 4825-4832. [12] P. R. Deshmukh, S. N. Pusawale, R. N. Bulakhe, C. D. Lokhande, Supercapacative performance of hydrous ruthenium oxide (RuO2.nH2O) thin films synthesized by chemical route at low temperature, Bull.Mat. sci., 36(2013) 1171-1176.
Science Direct Materials Today: Proceedings 18 (2019) 2848–2858
www.materialstoday.com/proceedings
ICMPC-2019
Effect Of Surface Treatments On Supercapacitive Performance Of SnO2-RuO2 Composite Thin Films S.N. Pusawaleab*, Prashant S. Jadhavab a
Rajarambapu Institute of Technology, Sakharale, Maharashtra. b Shivaji University, Kolhapur , Maharashtra.
Abstract
In the present work, we have adopted a simple and inexpensive route to prepare tin oxide-ruthenium oxide (SnO2RuO2) composite thin film electrodes via a chemical approach. Further, the fabricated films are treated with different surface treatments in order to tune their morphology and see its effect on the supercapacitor properties. The surface treatments that we used are annealing in air, ultrasonic weltering in NaOH and anodization. It is observed that with air annealing the specific capacitance of the pristine electrode is decreased from 166 F/g to 12 F/g this is due to the loss of hydrous content from the electrode. The electrode then has undergone another surface treatment of ultrasonic weltering where there is change in the morphology of the electrode. The specific capacitance is decreased to 106 F/g for ultrasonically weltered electrode. The effect of anodization treatment is then studied and it is observed that with this treatment the specific capacitance of the electrode is increased to 269 F/g. The increase in the specific capacitance is attributed to the comparatively smooth morphology and improvement in the conductivity of the electrode. This shows that the supercapacitive performance of the electrode can be improved by using different kind of surface treatments. In our research anodization is found to be a good surface treatment to enhance the specific capacitance of the pristine electrode. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Thin films; Supercapacitor, Chemical Synthesis; Surface treatments.
1. Introduction Supercapacitors are in growing demand nowadays due to their wide range of applications in hybrid electric vehicles, telecommunications, particularly associated with cellular phones for a reduction of the size of the batteries 1
Corresponding author. E-mail address: [email protected]
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
2849
[1]. Various materials have been researched for their supercapacitive performance such as metal oxides, polymers, and carbon. Among these hydrous form of RuO2 has shown excellent supercapacitive performance but due to its low cost, it restricts its commercial application. In order to reduce the cost, other metal oxides such as TiO2, SnO2, and MnO2 etc. were combined with RuO2. It was observed that the performance of supercapacitor electrode is strongly depend upon the active materials involved, their reversible redox transitions between various oxidation states and morphology [2]. The morphology of the supercapacitor electrode is an important aspect, as it is well known that the porous morphology of the electrode is useful for supercapacitor application because such morphology provides higher effective surface area. The morphology and hence the supercapacitive performance of electrode can be tuned by various surface treatments. In earlier studies, specific capacitance of ruthenium oxide has been enhanced by surface treatments like annealing in air [3, 4] electrochemical anodization in aqueous media [5] and ultrasonic weltering in NaOH [6]. In the present work, tin oxide-ruthenium oxide (SnO2-RuO2) composite electrodes prepared by SILAR (Successive ionic layer adsorption and reaction) and CBD (chemical bath deposition) methods are treated by various surface treatments such as annealing in air, ultrasonic weltering in NaOH and anodization. The effect of these surface treatments on the morphology, wettability and specific capacitance of the SnO2-RuO2 composite film is studied. 2. Experimental 2.1 Preparation of SnO2-RuO2 composite films and surface treatments applied The optimized SnO2–RuO2 composite films showing maximum specific capacitance value were prepared by SILAR (SnO2: RuO2= 1:3) and CBD (15 vol%) methods as described in our earlier work [7, 8]. The deposition was taken on large area stainless steel (> 16 cm2 ) substrates. The substrate is then cut into 4 identical substrates of ~ 4 cm2 area and used for surface treatment study. For air annealing, SnO2-RuO2 composite electrode was annealed in air at 423 K for 2 h. For ultrasonic weltering, the substrate coated with SnO2-RuO2 was ultrasonically weltered in 1 M NaOH for 30 min in ultrasonic cleaner and the anodization treatment was carried out in 0.1 M H2SO4 at +1.2 V for 1.30 h using potentiostat/ Galvanostat. It was observed that the SnO2-RuO2 composite film prepared by SILAR is unstable in NaOH solution so that the ultrasonic weltering was not done for SILAR deposited SnO2-RuO2 composite film. 2.2 Characterization techniques The microstructure of the films was observed using scanning electron microscopy (JEOL, JEM-6360, Japan). Static water contact angle measurement was carried out using RameHart Instrument Co., USA equipped with CCD camera. The transmission electron micrograph was obtained by Jeol JEM-2100F unit. The electrochemical study was performed in a three-electrode configuration cell consisting of SnO2-RuO2 as a working electrode, platinum as a counter electrode and saturated calomel electrode (SCE) as a reference electrode.
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3. Result 3.1 Effect of Surface Treatments on SnO2-RuO2 Composite Film Prepared by SILAR Method 3.1.1 Effect of Air Annealing The morphology of pristine and air annealed SnO2-RuO2 composite film prepared by SILAR method is shown in Fig. 1 (a, b). The pristine SnO2-RuO2 composite film surface contains porous irregular shaped agglomerated morphology, which changed to a granular and comparatively smooth surface with overgrowth of particles after air annealing. The contact angle image for pristine and air annealed SnO2-RuO2 composite film is shown in Fig. 2 (a, b). The contact angle for pristine SnO2-RuO2 composite film is 1210 changed to 130 for annealed SnO2-RuO2 composite film, which shows the hydrophobic nature of the composite film is changed to hydrophilic after air annealing. It was observed that the surfaces with high surface energy are hydrophilic. As with air annealing, there is possibility of formation of nanocrystalline structure for SnO2-RuO2 composite, the nanocrystalline surface has greater surface energy, resulting in the decrease in water contact angle [9]. The supercapacitive performance of annealed SnO2-RuO2 composite electrode is studied using cyclic voltammetry (CV) in 0.5 M H2SO4 electrolyte at 5 mV/s scan rate in the potential range of -0.2 to +0.6 V vs. SCE. The cyclic voltammogram (Fig. 3) showed that specific capacitance is decreased from 183 to 67 F/g for annealed SnO2-RuO2 composite electrode compared with pristine electrode. The loss in specific capacitance value is due to the a significant loss in the water content resulting in a more ordered structure which render a higher barrier for proton diffusion in comparison with their pristine structure [10]. Also, there may be formation of nanocrystalline structure with decrease in defects (i.e. electroactive sites), decreasing the specific capacitance of electroactive species [6].
Fig. 1: The morphology of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
2851
(a)- Pristine (b)- Air Annealed
1.0
-2
Current density (mA.cm )
Fig. 2: The water contact angle images of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
0.5
0.0 (a) (b)
-0.5
-0.2
0.0
0.2
0.4
0.6
Voltage (V vs.SCE)
Fig. 3: The CV curves for pristine and air annealed SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 5 mV/s between -0.2 to +0.6 V vs. SCE.
3.1.2 Effect of Anodization The effect of anodization on the morphology and wettability of SnO2-RuO2 composite film is studied. Fig. 4 (a) shows the morphology of SnO2-RuO2 composite film after anodization treatment. The spongy and porous morphology is observed for SnO2-RuO2 composite film after anodization. The water contact angle decreased to 720 compared with pristine SnO2-RuO2 composite film as observed from Fig. 4 (b). The CV curve for anodized SnO2-RuO2 composite electrode is shown in Fig. 5. From the CV curve, decrease in voltammetric current is observed for anodized SnO2-RuO2 composite electrode. The specific capacitance decreased from 183 to 106 F/g for anodized SnO2-RuO2 composite electrode compared with pristine composite electrode.
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Fig. 4: (a) The morphology and (b) water contact angle image of anodized SnO2-RuO2 composite film.
Pristine Anodized
-2
Current density (mA.cm )
1.0
0.5
0.0 (a) (b)
-0.5 -0.2
0.0
0.2
0.4
0.6
Voltage (V vs. SCE) Fig. 5: The CV curves for pristine and anodized SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 5 mV/s between -0.2 to +0.6 V vs. SCE.
The comparative study of surface treatments on the contact angle and specific capacitance value of SnO2–RuO2 composite is shown in table 1.
S.N. Pusawale and P.S. Jadhav / Materials Today: Proceedings 18 (2019) 2848–2858
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Table 1 Effect of surface treatments on specific capacitance value of SILAR deposited SnO2-RuO2 composite electrode. Specific Capacitance (F/g) Sr. Surface treatment Sample Area Contact (cm2)
No.
Angle (0)
1
Pristine
1
121
183
2.
Air annealing (423 K, 2 h)
1
13
67
3.
Anodization (0.1M H2SO4 at +1.2 V vs.
1
72
106
SCE for 1.30 h)
3.2 Effect of Surface Treatment on SnO2-RuO2 Composite Film prepared by CBD Method 3.2.1 Effect of Air Annealing In general, hydrous ruthenium oxide annealed in the temperature region close to its crystallization temperature showed a very high specific capacitance (≥720 F/g) [3]. This has been attributed to the local structures of hydrous ruthenium oxide retaining facile transport pathways for both protons and electrons [11]. The SEM images for pristine and air annealed SnO2-RuO2 composite films are shown in Fig. 6 (a, b) and water contact angle image for pristine SnO2-RuO2 composite film prepared by CBD method are shown in Fig. 7 (a, b). The larger pits observed in case of pristine SnO2-RuO2 composite electrode is vanished in annealed electrode. There is no much difference in water contact angle of pristine and annealed SnO2–RuO2 composite electrode. The CV curve for pristine and annealed SnO2-RuO2 composite electrode in the potential range of 0 to +0.8 V vs. SCE at 20 mV/s in 0.5 M H2SO4 electrolyte is shown in Fig. 8. The current was reduced significantly for annealed composite electrode reducing its specific capacitance value from 166 to 12 F/g. The significant decrease in specific capacitance value after annealing is attributed to the loss of hydrous content from the sample [12].
Fig. 6: The morphologies of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
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2
(a)- Pristine (b)- Air Annealed
-2
Current density (mA.cm )
Fig. 7: The water contact angle images of (a) pristine and (b) after air annealing for SnO2-RuO2 composite film.
1
0 (a)
-1
(b)
-2 0.0
0.2
0.4
0.6
0.8
Voltage (V vs. SCE)
Fig. 8: The CV curves for pristine and annealed SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 20 mV/s between 0 to +0.8 V vs. SCE. 3.2.2 Effect of Ultrasonic Weltering The effect of ultrasonic weltering in NaOH on SnO2-RuO2 composite electrode is studied. Fig. 9 (a, b) shows the surface morphology and water contact angle image for ultrasonically weltered SnO2-RuO2 composite electrode respectively. The bigger pits and elongated structure observed for pristine SnO2-RuO2 composite is vanished for ultrasonically weltered composite electrode with small pits distributed all over the surface. The water contact angle for ultrasonically weltered SnO2-RuO2 composite film is not much altered with slight decrease compared with pristine composite film.
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Fig. 10 shows the CV curves for pristine and ultrasonically weltered SnO2-RuO2 composite electrode. The specific capacitance value is decreased from 166 to 106 F/g for ultrasonically weltered SnO2-RuO2 composite electrode compared with pristine electrode. This means the ultrasonic weltering treatment is not suitable for SnO2RuO2 composite electrode as decrease in specific capacitance value was observed. Slight loss in weight of deposited film was observed after ultrasonic treatment due to the removal of unbound surface particles.
Fig. 9: (a) The morphology and (b) water contact angle image of ultrasonically weltered SnO2-RuO2 composite film.
(a)- Pristine (b)- Ultrasonic W eltered
-2
Current density (mA.cm )
2
1
0
-1
(a) (b)
-2 0.0
0.2
0.4
0.6
0.8
Voltage (V vs. SCE) Fig. 10: The CV curves for pristine and ultrasonically weltered SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 20 mV/s between 0 to +0.8 V vs. SCE.
3.2.3 Effect of Anodization The effect of anodization on SnO2-RuO2 composite electrode is studied. Fig. 11 (a, b) shows the morphology and contact angle image for SnO2-RuO2 composite electrode after anodization. The morphology of the
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electrode is changed from rough with irregular pits and elongated structure to relatively smooth surface covered all over the substrate after the anodization. The hydrophilic surface of pristine SnO2-RuO2 composite electrode was changed to superhydrophilic with water contact angle ~70. The CV curve for pristine and anodized SnO2-RuO2 electrode is shown in Fig. 12. From which it is observed that there is an increase in current response for SnO2-RuO2 electrode after anodization. There is possibility of presence of some chloride precursors in pristine samples, with anodization there is formation of impurity-free SnO2-RuO2, which improves the conductivity. Also as the surface is smooth and porous the electrolyte can easily access the bulk of the electrode, which results into maximum current response. [5]. Thus, anodization method is found to be useful surface treatment for SnO2-RuO2 composite electrode prepared by CBD method.
-2
Current density (mA.cm )
Fig. 11: (a) The morphology and (b) water contact angle image of anodized SnO2-RuO2 composite Film.
3.0
(a)- Pristine (b)- Anodized
1.5 0.0 -1.5
(a) (b)
-3.0 -4.5 0.0
0.2
0.4
0.6
0.8
Voltage (V vs. SCE) Fig. 12: The CV curves for pristine and anodized SnO2-RuO2 composite electrode in 0.5 M H2SO4 electrolyte at 20 mV/s between 0 to +0.8 V vs. SCE.
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The comparative study of surface treatments on the contact angle and specific capacitance value of SnO2–RuO2 composite is shown in Table 2. Table 2: Effect of surface treatments on specific capacitance value of CBD deposited SnO2-RuO2 Sr.
Surface Treatment
Sample
Contact 2
No.
0
Specific
Area (cm )
Angle ( )
Capacitance (F/g)
1
Pristine
1
14
166
2.
Air annealing (423 K, 2 h)
1
13
12
3.
Ultrasonic weltering (in 1 M NaOH for 30
1
12
106
1
7
269
min) 4.
Anodization (0.1 M H2SO4 at +1.2 V vs. SCE for 1.30 h)
Conclusions The effect of surface treatments on the morphology, wettability and specific capacitance on SnO2-RuO2 composite films deposited by SILAR and CBD method is studied successfully. It is observed that the morphology of the SnO2-RuO2 composite film deposited by SILAR method changed with annealing and anodization, in addition, the hydrophobic surface of pristine composite film changed to hydrophilic. The specific capacitance value decreased for both annealed and anodized SnO2-RuO2 composite electrode deposited by SILAR method. In case of SnO2-RuO2 composite films deposited by CBD method, the surface treatments changed the morphology to relatively smooth surface. The decrease in specific capacitance is observed for annealed and ultrasonically weltered SnO2-RuO2 composite films deposited by CBD method. However, with anodization treatment, the specific capacitance of the composite electrode deposited by CBD method is increased from 166 to 269 F/g. Thus anodization is found to be useful surface treatment for this electrode. References
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