- Email: [email protected]
MnO2@SnO2 core–shell heterostructured nanorods for supercapacitors
Materials Letters 130 (2014) 107–110
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
MnO2@SnO2 core–shell heterostructured nanorods for supercapacitors Y.M. Dai a,b,1, S.C. Tang a,1, J.Q. Peng b, H.Y. Chen b, Z.X. Ba b, Y.J. Ma a, X.K. Meng a,n a Institute of Materials Engineering, National Laboratory of Solid State Microstructures and College of Engineering and Applied Sciences, Nanjing University, Jiangsu, PR China b School of Materials Engineering, Nanjing Institute of Technology, Jiangsu, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 29 March 2014 Accepted 8 May 2014 Available online 23 May 2014
A facile, low-cost synthesis of MnO2@SnO2 core–shell heterostructured nanorods with superior supercapacitance is proposed. The synthesis involves sensitizing MnO2 nanorods with an aqueous SnCl2 solution to ensure the formation of a thin, uniform, and complete shell layer. The SnO2 coatings have rough surfaces and their thickness is about 18 nm. The MnO2@SnO2 composites have a specific capacitance of 367.5 F/g at 50 mV/s in 1 M Na2SO4, which is about four and six times of the pure MnO2 nanorods and SnO2 products. Meanwhile, they have 91.3% capacitance retention over 2000 cycles, which is much better than pure MnO2 nanorods. The remarkable performances with a low-cost imply that they have potential for supercapacitors applications. & 2014 Elsevier B.V. All rights reserved.
Keywords: Supercapacitors Manganese oxide Tin oxide Nanocomposites Energy storage and conversion
1. Introduction Based on their advantages in energy storage comparing with batteries due to high power density, and long cycle life, supercapacitors are promising in future high-power applications [1,2]. Developing electrode materials with high specific capacitance (SC), good long-term stability and low cost have gained much interest. The low SC and high cost limit practical applications of carbon materials, while metal oxides have ten times SC compared them due to pseudocapacitance mechanism [3]. Although RuO2 has the best performance among the reported metal oxides, the extremely high cost limits its commercial applications [4]. Base metal oxides such as MnO2 are the most promising alternatives for their high energy density, low cost and environmental compatibility [5]. However, actual SC of MnO2 is too low for its poor native electrical conductivity (EC) [6]. Combining them with conductive materials [7,8] are effective approaches to enhance the EC. For example, electrochemical growth of MnO2 on nano-porous gold film [9] can improve SC approaching the theoretical value (1370 F/g) [10]. However, an interfacial force between MnO2 and the metal frame is weak and especially the high proportion of noble metals in composites results in a high cost. As a comparison, a combination of MnO2 with conductive metal oxides can improve SC while still keeping a low cost.
n
Corresponding author. Tel.: þ 86 25 83685585; fax: þ 86 25 83595535. E-mail address: [email protected] (X.K. Meng). 1 These authors contributed equally.
http://dx.doi.org/10.1016/j.matlet.2014.05.090 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Recently, we report that a hierarchical MnO2 microstructure being covered with conductive Ag2O nanoparticles have a high SC at rapid charging–discharging and long-term durability [11]. Inspired by this, surface coating of MnO2 nano/microstructures via conductive metal oxides is an effective route to enhance electrochemical performances. However, due to an absence of surface functional groups, it is still a challenge to grow uniform nanocoatings on MnO2 nanostructures via heterogeneous nucleation and growth process. As one non-toxic and low-cost electrode material, SnO2 is attracting many attentions in supercapacitors due to its high EC and chemical stability [12]. In this work, MnO2@SnO2 core–shell heterostructured nanorods are prepared via a two-step process. The synthesis includes sensitizing pre-prepared MnO2 nanorods by SnCl2 to obtain thin Sn(OH)Cl coating, and a subsequent drying process leads to conductive and rough SnO2 coatings. To the best of our knowledge, a combination of MnO2 with SnO2 in nanoscale has been few studied. The electrochemical performances of the MnO2@SnO2 composites are also investigated.
2. Experimental Preparation of MnO2 nanorods: To prepare MnO2 nanorods, 20 mmol KClO3 and 10 mmol MnSO4 were dissolved in 40 mL deionized water. Then the solution was transferred into a 50 mL Teflon-lined stainless steel autoclave, the autoclave was then heated at 140 1C for 12 h. Finally, the precipitates were collected by centrifugation, washed repeatedly with deionized water. MnO2@SnO2 core–shell heterostructured nanorods: The above MnO2 nanorods product was added into a SnCl2 solution
108
Y.M. Dai et al. / Materials Letters 130 (2014) 107–110
Fig. 1. SEM images of (a) MnO2 nanorods and (b) MnO2@SnO2 core–shell heterostructured nanorods, the inset magnifies the marked rectangles; (c) TEM image and (d) SAED pattern of the MnO2@SnO2 core–shell heterostructured nanorods.
(0.3 mol/L, 5 mL), then ultrasonically irradiated at 25 1C for 30 min. The precipitates were collected and finally dried at 150 1C for 12 h. Characterizations: The morphology and microstructure of the products were characterized by field-emission scanning electron microscopy (SEM, S-4800, Hitachi) at 10 kV, transmission electron microscopy (TEM, JEM-2100, JEOL) at 200 kV, X-ray diffraction (XRD, Ultima-IV, Rigaku) using Cu Kα radiation at a scan rate of 101/min, and X-ray photoelectron spectroscopy (XPS, ESCA2000, Thermo) with a CLAM4 hemispherical analyser. Raman spectra were tested on a confocal microscopy Raman system (Invia, Renishaw) with 514 nm wavelength laser. Electrochemical measurements: The cyclic voltammetry (CV) and galvanostatic measurements were performed on a workstation (CHI660D, Chenhua), using a three electrode mode in a 1 M Na2SO4 aqueous solution at 25 1C. The working electrodes were prepared by grinding the active materials, acetylene black and polytetrafluoroethylene (mass ratio is 7:2:1). Then, the mixture was rolled into 1 cm2 film and coated onto Ni foam to form the electrode layer by drying at 120 1C for 10 h. After that, the electrode was compressed with the pressure of 10 MPa. The counter and reference electrodes were Pt and Ag/AgCl, respectively. The potential range for CV tests was 0 to 1 V at a scan rate of 50 mV/s. SC values were calculated using the following formula. SC ¼ Q =2vmΔV
ð1Þ
where Q is the integral area of the CV curve, v is the scan rate, m is the mass of active material, and ΔV is the potential window. Galvanostatic measurements and capacitance retention were tested at a charge/discharge current density of 5 A/g, and a potential window of 0 to 1 V. Capacitance retention was measured on a battery analyser (C5-100, BettaTeQ). The anode is same with the working electrode described above, and the cathode is
graphite sheet. The separator film is polyethylene (PE) fibrous paper and the electrolyte is 1 M Na2SO4 aqueous solution. 3. Results and discussion Reaction mechanism: The MnO2 nanorods with uniform size and good stability can be acquired. Sensitizing MnO2 nanorods by SnCl2, thin and uniform Sn(OH)Cl coatings will be generated on the surface of the MnO2 nanorod. The Sn(OH)Cl layer is not stable and it will be oxidized to SnO2, the released gas will make the layer loose. The reactions [13,14] are as follows. 3MnSO4 þ2KClO3 þ3H2O-3MnO2↓ þCl2↑ þK2SO4 þ2H2SO4
(2)
SnCl2 þ H2O-Sn(OH)Cl↓ þHCl↑
(3)
Sn(OH)Cl þH2O-SnO2 þHCl↑ þH2↑
(4)
Microscopic analysis: As shown in Fig. 1a, the MnO2 nanorods have an average diameter of 4575 nm. After SnO2 coating, the diameters of the nanorods are 63 74 nm (Fig. 1b). The increment ( 18 nm) in diameter is the thickness of SnO2 coatings. The image also shows the coatings have densely covered cracks that are beneficial to the diffusion of electrolyte. TEM image (Fig. 1c) shows that the diameters of the composites are 7075 nm, consistent with the SEM results. As seen from SAED pattern of the composites (Fig. 1d), two distinct diffraction spots reveal that the as-product is composed of MnO2 and SnO2. Fig. 2a shows XRD patterns of the two samples. All the diffraction peaks of the MnO2 nanorods correspond to the crystal planes of MnO2 (JCPDS no. 44-0141). In the pattern of the composites, there are diffraction peaks corresponding to the planes of SnO2 (JCPDS no. 44-1445) besides MnO2. Combined with
Y.M. Dai et al. / Materials Letters 130 (2014) 107–110
109
Fig. 2. (a) XRD patterns, (b) Raman spectra and (c) XPS surveys of the pure SnO2, MnO2 nanorods and MnO2@SnO2 core–shell heterostructured nanorods; (d)–(f) XPS spectra of Mn 2p, Sn 3d and O 1s of the MnO2@SnO2 core–shell heterostructured nanorods.
the SEM and SAED analysis, the composites are confirmed to have a core–shell (MnO2 nanorods@SnO2 coatings) heterostructure. In Raman spectra (Fig. 2b), the band at 347 cm 1 in heterostructured nanorods was not found in pure SnO2 or MnO2 nanorods, which may be attributed to the new stretching vibration of Sn–O–Mn [15]. XPS surveys spectra of the two samples (Fig. 2c) show that they both have been detected peaks of Mn 2p1/2, Mn 2p3/2 and O 1s. The
composites also have Sn 3p1/2, Sn 3p3/2, Sn 3d3/2 and Sn 3d5/2 peaks. In addition, the XPS results reveal that the atomic percentage of Sn in the composites is 18.2%, which is much higher than the EDS result of 4.0%. Fig. 2d–f are the high resolution spectra of Mn 2p, Sn 3d and O1s of the composites. The results further confirm SnO2 coatings are on the surface of MnO2 cores. Electrochemical performance: The CV curves of these samples are shown in Fig. 3a. The SC of the composites (367.5 F/g) is four
110
Y.M. Dai et al. / Materials Letters 130 (2014) 107–110
measurements showed that the order of potential jumps [16] Δφ1, Δφ2 and Δφ3 for pure SnO2, MnO2 nanorods and composites is Δφ1 o Δφ3 o Δφ2 (Fig. 3b). The result indicates that the composites have higher conductivity than the MnO2 nanorods. The conducive coatings enhance SC of the composites. Fig. 3c shows the capacitance retention of the two samples. The composites exhibits excellent stability, its capacitance retention is still 91.3% over 2000 cycles. However, the capacitance retention of the MnO2 nanorods decreases monotonously, and the value is only 74.6% over 2000 cycles.
4. Conclusions In summary, a simple method is developed to fabricate MnO2@SnO2 core–shell heterostructured nanorods with a superior SC of 367.5 F/g at 50 mV/s, which is four times of the MnO2 nanorods. Regarding durability, the composites have 91.3% capacitance retention over 2000 cycles, which is much better than the MnO2 nanorods. The heterostructure in MnO2@SnO2 composites plays a key role for the enhancement of the SC and the structural stability.
Acknowledgments The authors kindly acknowledge the joint support by the PAPD, the Fundamental Research Funds for the Central Universities, the Natural Science Research Program for Universities of Jiangsu Province, the Research Innovation Program for College Students of Jiangsu Province, the Innovation Fund of Jiangsu Province, the National Natural Science Foundation of China, and the State Key Program for Basic Research of China. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] Fig. 3. Electrochemical performance of the pure SnO2, MnO2 nanorods and MnO2@SnO2 core–shell heterostructured nanorods. (a) CV curves at 50 mV/s. (b) Galvanostatic charge/discharge curves at 5 A/g. (c) Capacitance retention at 5 A/g over 2000 cycles.
times of the MnO2 nanorods (85.1 F/g) and six times of the pure SnO2 (60.2 F/g). This may be attributed to the structure of Sn–O–Mn enhance the SC of electrode materials. Galvanostatic
[16]
Yang PH, Xiao X, Li YZ, Ding Y, Qiang PF, et al. ACS Nano 2013;7:2617–26. Mai LQ, Yang F, Zhao YL, Xu X, Xu L, et al. Nat Commun 2011;2:1387. Burke AJ. Power Sources 2000;91:37–50. Xia H, Meng YS, Yuan GL, Cui C, Luc L. Electrochem Solid State 2012;15:A60–3. Wu MS. Appl Phys Lett 2005;87:153102. Zhao DD, Zhao YQ, Zhang X, Xu CL, Peng Y, et al. Mater Lett 2013;107:115–8. Yang PH, Li YZ, Lin ZY, Ding Y, Yue S, et al. J Mater Chem A 2014;2:595–9. Dai YM, Tang SC, Ba ZX, Zhu SS, Wang Q, et al. Mater Lett 2014;117:104–7. Lang XY, Hirata A, Fujita T, Chen MW. Nat Nanotechnol 2011;6:232–6. Toupin M, Brousse T, Belanger D. Chem Mater 2004;16:3184–90. Dai YM, Tang SC, Vongehr S, Meng XK. ACS Sustainable Chem Eng 2014;2:692–8. Li RZ, Ren X, Zhang F, Du C, Liu JP. Chem Commun 2012;48:5010–2. Khan Y, Durrani SK, Mehmood M, Khan MR. J Mater Res 2011;26:2268–75. Lee JS, Kim YJ, Lee YU, Cho SH, Kim YH, et al. ECS Trans 2010;33:283–8. Lou FL, Zhou HT, Huang F, Vullum-Bruer F, Tran TD, et al. J Mater Chem A 2013;1:3757–67. Ma SB, Nam KW, Yoon WS, Yang XQ, Ahn KY, et al. Electrochem Commun 2007;9:2807–11.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
MnO2@SnO2 core–shell heterostructured nanorods for supercapacitors Y.M. Dai a,b,1, S.C. Tang a,1, J.Q. Peng b, H.Y. Chen b, Z.X. Ba b, Y.J. Ma a, X.K. Meng a,n a Institute of Materials Engineering, National Laboratory of Solid State Microstructures and College of Engineering and Applied Sciences, Nanjing University, Jiangsu, PR China b School of Materials Engineering, Nanjing Institute of Technology, Jiangsu, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 29 March 2014 Accepted 8 May 2014 Available online 23 May 2014
A facile, low-cost synthesis of MnO2@SnO2 core–shell heterostructured nanorods with superior supercapacitance is proposed. The synthesis involves sensitizing MnO2 nanorods with an aqueous SnCl2 solution to ensure the formation of a thin, uniform, and complete shell layer. The SnO2 coatings have rough surfaces and their thickness is about 18 nm. The MnO2@SnO2 composites have a specific capacitance of 367.5 F/g at 50 mV/s in 1 M Na2SO4, which is about four and six times of the pure MnO2 nanorods and SnO2 products. Meanwhile, they have 91.3% capacitance retention over 2000 cycles, which is much better than pure MnO2 nanorods. The remarkable performances with a low-cost imply that they have potential for supercapacitors applications. & 2014 Elsevier B.V. All rights reserved.
Keywords: Supercapacitors Manganese oxide Tin oxide Nanocomposites Energy storage and conversion
1. Introduction Based on their advantages in energy storage comparing with batteries due to high power density, and long cycle life, supercapacitors are promising in future high-power applications [1,2]. Developing electrode materials with high specific capacitance (SC), good long-term stability and low cost have gained much interest. The low SC and high cost limit practical applications of carbon materials, while metal oxides have ten times SC compared them due to pseudocapacitance mechanism [3]. Although RuO2 has the best performance among the reported metal oxides, the extremely high cost limits its commercial applications [4]. Base metal oxides such as MnO2 are the most promising alternatives for their high energy density, low cost and environmental compatibility [5]. However, actual SC of MnO2 is too low for its poor native electrical conductivity (EC) [6]. Combining them with conductive materials [7,8] are effective approaches to enhance the EC. For example, electrochemical growth of MnO2 on nano-porous gold film [9] can improve SC approaching the theoretical value (1370 F/g) [10]. However, an interfacial force between MnO2 and the metal frame is weak and especially the high proportion of noble metals in composites results in a high cost. As a comparison, a combination of MnO2 with conductive metal oxides can improve SC while still keeping a low cost.
n
Corresponding author. Tel.: þ 86 25 83685585; fax: þ 86 25 83595535. E-mail address: [email protected] (X.K. Meng). 1 These authors contributed equally.
http://dx.doi.org/10.1016/j.matlet.2014.05.090 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Recently, we report that a hierarchical MnO2 microstructure being covered with conductive Ag2O nanoparticles have a high SC at rapid charging–discharging and long-term durability [11]. Inspired by this, surface coating of MnO2 nano/microstructures via conductive metal oxides is an effective route to enhance electrochemical performances. However, due to an absence of surface functional groups, it is still a challenge to grow uniform nanocoatings on MnO2 nanostructures via heterogeneous nucleation and growth process. As one non-toxic and low-cost electrode material, SnO2 is attracting many attentions in supercapacitors due to its high EC and chemical stability [12]. In this work, MnO2@SnO2 core–shell heterostructured nanorods are prepared via a two-step process. The synthesis includes sensitizing pre-prepared MnO2 nanorods by SnCl2 to obtain thin Sn(OH)Cl coating, and a subsequent drying process leads to conductive and rough SnO2 coatings. To the best of our knowledge, a combination of MnO2 with SnO2 in nanoscale has been few studied. The electrochemical performances of the MnO2@SnO2 composites are also investigated.
2. Experimental Preparation of MnO2 nanorods: To prepare MnO2 nanorods, 20 mmol KClO3 and 10 mmol MnSO4 were dissolved in 40 mL deionized water. Then the solution was transferred into a 50 mL Teflon-lined stainless steel autoclave, the autoclave was then heated at 140 1C for 12 h. Finally, the precipitates were collected by centrifugation, washed repeatedly with deionized water. MnO2@SnO2 core–shell heterostructured nanorods: The above MnO2 nanorods product was added into a SnCl2 solution
108
Y.M. Dai et al. / Materials Letters 130 (2014) 107–110
Fig. 1. SEM images of (a) MnO2 nanorods and (b) MnO2@SnO2 core–shell heterostructured nanorods, the inset magnifies the marked rectangles; (c) TEM image and (d) SAED pattern of the MnO2@SnO2 core–shell heterostructured nanorods.
(0.3 mol/L, 5 mL), then ultrasonically irradiated at 25 1C for 30 min. The precipitates were collected and finally dried at 150 1C for 12 h. Characterizations: The morphology and microstructure of the products were characterized by field-emission scanning electron microscopy (SEM, S-4800, Hitachi) at 10 kV, transmission electron microscopy (TEM, JEM-2100, JEOL) at 200 kV, X-ray diffraction (XRD, Ultima-IV, Rigaku) using Cu Kα radiation at a scan rate of 101/min, and X-ray photoelectron spectroscopy (XPS, ESCA2000, Thermo) with a CLAM4 hemispherical analyser. Raman spectra were tested on a confocal microscopy Raman system (Invia, Renishaw) with 514 nm wavelength laser. Electrochemical measurements: The cyclic voltammetry (CV) and galvanostatic measurements were performed on a workstation (CHI660D, Chenhua), using a three electrode mode in a 1 M Na2SO4 aqueous solution at 25 1C. The working electrodes were prepared by grinding the active materials, acetylene black and polytetrafluoroethylene (mass ratio is 7:2:1). Then, the mixture was rolled into 1 cm2 film and coated onto Ni foam to form the electrode layer by drying at 120 1C for 10 h. After that, the electrode was compressed with the pressure of 10 MPa. The counter and reference electrodes were Pt and Ag/AgCl, respectively. The potential range for CV tests was 0 to 1 V at a scan rate of 50 mV/s. SC values were calculated using the following formula. SC ¼ Q =2vmΔV
ð1Þ
where Q is the integral area of the CV curve, v is the scan rate, m is the mass of active material, and ΔV is the potential window. Galvanostatic measurements and capacitance retention were tested at a charge/discharge current density of 5 A/g, and a potential window of 0 to 1 V. Capacitance retention was measured on a battery analyser (C5-100, BettaTeQ). The anode is same with the working electrode described above, and the cathode is
graphite sheet. The separator film is polyethylene (PE) fibrous paper and the electrolyte is 1 M Na2SO4 aqueous solution. 3. Results and discussion Reaction mechanism: The MnO2 nanorods with uniform size and good stability can be acquired. Sensitizing MnO2 nanorods by SnCl2, thin and uniform Sn(OH)Cl coatings will be generated on the surface of the MnO2 nanorod. The Sn(OH)Cl layer is not stable and it will be oxidized to SnO2, the released gas will make the layer loose. The reactions [13,14] are as follows. 3MnSO4 þ2KClO3 þ3H2O-3MnO2↓ þCl2↑ þK2SO4 þ2H2SO4
(2)
SnCl2 þ H2O-Sn(OH)Cl↓ þHCl↑
(3)
Sn(OH)Cl þH2O-SnO2 þHCl↑ þH2↑
(4)
Microscopic analysis: As shown in Fig. 1a, the MnO2 nanorods have an average diameter of 4575 nm. After SnO2 coating, the diameters of the nanorods are 63 74 nm (Fig. 1b). The increment ( 18 nm) in diameter is the thickness of SnO2 coatings. The image also shows the coatings have densely covered cracks that are beneficial to the diffusion of electrolyte. TEM image (Fig. 1c) shows that the diameters of the composites are 7075 nm, consistent with the SEM results. As seen from SAED pattern of the composites (Fig. 1d), two distinct diffraction spots reveal that the as-product is composed of MnO2 and SnO2. Fig. 2a shows XRD patterns of the two samples. All the diffraction peaks of the MnO2 nanorods correspond to the crystal planes of MnO2 (JCPDS no. 44-0141). In the pattern of the composites, there are diffraction peaks corresponding to the planes of SnO2 (JCPDS no. 44-1445) besides MnO2. Combined with
Y.M. Dai et al. / Materials Letters 130 (2014) 107–110
109
Fig. 2. (a) XRD patterns, (b) Raman spectra and (c) XPS surveys of the pure SnO2, MnO2 nanorods and MnO2@SnO2 core–shell heterostructured nanorods; (d)–(f) XPS spectra of Mn 2p, Sn 3d and O 1s of the MnO2@SnO2 core–shell heterostructured nanorods.
the SEM and SAED analysis, the composites are confirmed to have a core–shell (MnO2 nanorods@SnO2 coatings) heterostructure. In Raman spectra (Fig. 2b), the band at 347 cm 1 in heterostructured nanorods was not found in pure SnO2 or MnO2 nanorods, which may be attributed to the new stretching vibration of Sn–O–Mn [15]. XPS surveys spectra of the two samples (Fig. 2c) show that they both have been detected peaks of Mn 2p1/2, Mn 2p3/2 and O 1s. The
composites also have Sn 3p1/2, Sn 3p3/2, Sn 3d3/2 and Sn 3d5/2 peaks. In addition, the XPS results reveal that the atomic percentage of Sn in the composites is 18.2%, which is much higher than the EDS result of 4.0%. Fig. 2d–f are the high resolution spectra of Mn 2p, Sn 3d and O1s of the composites. The results further confirm SnO2 coatings are on the surface of MnO2 cores. Electrochemical performance: The CV curves of these samples are shown in Fig. 3a. The SC of the composites (367.5 F/g) is four
110
Y.M. Dai et al. / Materials Letters 130 (2014) 107–110
measurements showed that the order of potential jumps [16] Δφ1, Δφ2 and Δφ3 for pure SnO2, MnO2 nanorods and composites is Δφ1 o Δφ3 o Δφ2 (Fig. 3b). The result indicates that the composites have higher conductivity than the MnO2 nanorods. The conducive coatings enhance SC of the composites. Fig. 3c shows the capacitance retention of the two samples. The composites exhibits excellent stability, its capacitance retention is still 91.3% over 2000 cycles. However, the capacitance retention of the MnO2 nanorods decreases monotonously, and the value is only 74.6% over 2000 cycles.
4. Conclusions In summary, a simple method is developed to fabricate MnO2@SnO2 core–shell heterostructured nanorods with a superior SC of 367.5 F/g at 50 mV/s, which is four times of the MnO2 nanorods. Regarding durability, the composites have 91.3% capacitance retention over 2000 cycles, which is much better than the MnO2 nanorods. The heterostructure in MnO2@SnO2 composites plays a key role for the enhancement of the SC and the structural stability.
Acknowledgments The authors kindly acknowledge the joint support by the PAPD, the Fundamental Research Funds for the Central Universities, the Natural Science Research Program for Universities of Jiangsu Province, the Research Innovation Program for College Students of Jiangsu Province, the Innovation Fund of Jiangsu Province, the National Natural Science Foundation of China, and the State Key Program for Basic Research of China. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] Fig. 3. Electrochemical performance of the pure SnO2, MnO2 nanorods and MnO2@SnO2 core–shell heterostructured nanorods. (a) CV curves at 50 mV/s. (b) Galvanostatic charge/discharge curves at 5 A/g. (c) Capacitance retention at 5 A/g over 2000 cycles.
times of the MnO2 nanorods (85.1 F/g) and six times of the pure SnO2 (60.2 F/g). This may be attributed to the structure of Sn–O–Mn enhance the SC of electrode materials. Galvanostatic
[16]
Yang PH, Xiao X, Li YZ, Ding Y, Qiang PF, et al. ACS Nano 2013;7:2617–26. Mai LQ, Yang F, Zhao YL, Xu X, Xu L, et al. Nat Commun 2011;2:1387. Burke AJ. Power Sources 2000;91:37–50. Xia H, Meng YS, Yuan GL, Cui C, Luc L. Electrochem Solid State 2012;15:A60–3. Wu MS. Appl Phys Lett 2005;87:153102. Zhao DD, Zhao YQ, Zhang X, Xu CL, Peng Y, et al. Mater Lett 2013;107:115–8. Yang PH, Li YZ, Lin ZY, Ding Y, Yue S, et al. J Mater Chem A 2014;2:595–9. Dai YM, Tang SC, Ba ZX, Zhu SS, Wang Q, et al. Mater Lett 2014;117:104–7. Lang XY, Hirata A, Fujita T, Chen MW. Nat Nanotechnol 2011;6:232–6. Toupin M, Brousse T, Belanger D. Chem Mater 2004;16:3184–90. Dai YM, Tang SC, Vongehr S, Meng XK. ACS Sustainable Chem Eng 2014;2:692–8. Li RZ, Ren X, Zhang F, Du C, Liu JP. Chem Commun 2012;48:5010–2. Khan Y, Durrani SK, Mehmood M, Khan MR. J Mater Res 2011;26:2268–75. Lee JS, Kim YJ, Lee YU, Cho SH, Kim YH, et al. ECS Trans 2010;33:283–8. Lou FL, Zhou HT, Huang F, Vullum-Bruer F, Tran TD, et al. J Mater Chem A 2013;1:3757–67. Ma SB, Nam KW, Yoon WS, Yang XQ, Ahn KY, et al. Electrochem Commun 2007;9:2807–11.