1.3 Synthesis of sputtered Î±-MnO2 nanorods. 1.4 Preparation of symmetric supercapacitor device. 1.5 Characterization. 1.6 Electrochemical characterization. 2.
Supporting Information Copyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, 2016
Performance of High Energy Density Symmetric Supercapacitor Based on Sputtered MnO2 Nanorods Ashwani Kumar+, Amit Sanger+, Arvind Kumar, Yogendra Kumar Mishra,* and Ramesh Chandra*
Table of Content: 1. Experimental Section: 1.1 Materials and Chemicals 1.2 Synthesis of Ag coated porous anodized alumina 1.3 Synthesis of sputtered α-MnO2 nanorods 1.4 Preparation of symmetric supercapacitor device 1.5 Characterization 1.6 Electrochemical characterization
2. Figure: FIGURE S1. (a) XRD pattern of α-MnO2 nanorods, and (b) Raman spectra of α-MnO2 nanorods. FIGURE S2. (a) SEM image of α-MnO2 nanorods at 200 and 100 nm scale. (b) SEM image of α-MnO2 nanorods with diameter of 27 nm and average lengths of 1.5-2 μm. (c) EDX elemental mapping of α-MnO2 nanorods. (d) TEM image of α-MnO2 nanorods. (e) High resolution TEM image of α-MnO2 nanorods. (f) SAED pattern of α-MnO2 nanorods. FIGURE S3. (a) Nitrogen adsorption-desorption isotherms of α-MnO2 nanorods. (b) Pore size distributions of the αMnO2 nanorods. FIGURE S4. XPS spectra of α-MnO2/Ag/AAO working electrode (a) full spectra and, (b) Ag 3d. FIGURE S5. CV curve of Ag/AAO current collector and α-MnO2/Ag/AAO working electrode at scan rate of 50 mV/s. FIGURE S6. CV curve of symmetric supercapacitor device measured at different potential window at a scan rate of 50 mV/s. FIGURE S7. (a) GCD curves for few initial and final cycles of symmetric device at 2 mA/cm2 current density. (b) CV curves of the symmetric device after charge/discharge cycles at a scan rate of 50 mV/s. FIGURE S8. (a) SEM image of α-MnO2/Ag/AAO working electrode after 3000 cycles. (b) EDX spectra and, (c) EDX elemental mapping.
3. Table: Table S1. Comparison of surface area of our MnO 2 with previously reported nanostructures produced by different synthetic routes. Table S2. Comparison of electrochemical performance of our MnO2 nanorods electrode with previously reported nanostructures using standard three-electrode cell. Table S3. Comparison of specific capacitances and energy density of the reported MnO 2/graphene and MnO2/other carbon nanomaterials composite-based electrodes. Table S4. Various performance parameters of the symmetric supercapacitor of the present work. Table S5. The energy density and power density based on mass of fully packaged cell device.
4. Calculations 5. Supplementary References
1. Experimental Section: 1.1 Materials and Chemicals Manganese (Mn) and silver (Ag) targets (2” diameter) of high purity (99.99%) were purchased from Testbourne Ltd. UK. The argon (Ar) and oxygen (O2) gas cylinder of high purity (99.9%) were obtained from Sigma Gases, India. Oxalic acid (H2C2O4), sodium sulphate (Na2SO4) and aluminium foil (0.3 mm thick) were obtained from Merck, India. Deionized water was used for electrochemical anodization. 1.2 Synthesis of Ag coated porous anodized alumina Aluminium foil were first degreased in acetone and ethanol by ultrasonication for 15 min and rinsed in deionized water. The anodizing step employed 0.3 M oxalic acid under a constant dc voltage of 80 V for 1 hour at 0° C. The schematic representation of anodizing cell is shown in author’s previous study. Unfortunately, the AAO template cannot be used as supercapacitor electrode because it is an insulator. However, the structural features of the AAO membrane provide a hint for the design of nanostructured electrode for supercapacitors. Therefore after anodization, deionized water rinsed porous AAO substrate was kept in the sputtering chamber at a distance of 5 cm from the Ag target. The sputtering chamber was initially evacuated to a base pressure of 2 × 10−6 Torr. Thereafter working pressure of sputtering chamber was kept constant at 10 mTorr by constant flow of Ar gas using mass flow controller (MKS). The deposition of Ag was carried out for a period of 5 sec by applying 50W sputtering power at room temperature. The resistance of the same can be reduced up to 1 Ω using the conformal coating of Ag nanoparticle. This electrode has two more important features such as the binder free and corrosion rate this electrode, i.e., good for current collector supercapacitor application.
1.3 Synthesis of sputtered α-MnO2 nanorods α-MnO2 nanorods were deposited directly on liquid nitrogen cooled cold finger made of oxygenfree high thermal conductivity (OFHC) copper by reactive DC sputtering technique (Scheme 1). The distance between target (Mn) and cold finger was kept at 4.5 cm. Prior to deposition, the sputtering chamber was initially evacuated to a base pressure of 5 × 10−7 Torr. The working pressure was kept constant at 30 mTorr by constant flow of Ar (40 sccm) and O2 (10 sccm) gas using mass flow controller. The deposition of α-MnO2 was carried out for a period of 1 hour by applying 60W sputtering power at -194 °C. After deposition, α-MnO2 nanorods were scratched carefully from cold finger at room temperature. 1.4 Preparation of symmetric supercapacitor device The working electrode was prepared by the same procedure with deposition of α-MnO2 nanorods for 30 min. directly on the Ag coated porous AAO current collector (Scheme 1). After deposition, the sample was taken out at room temperature and dried in oven at 80 °C for 5 hours. The working electrodes with an exposed area 1×1 cm2 were used in two electrode system cell with an electrode gap of 0.26 mm controlled by spacer. The loading mass of α-MnO2 was about 0.26 mg/cm2. The loading mass was calculated by taking difference between measured weight of the materials coated and uncoated Ag/AAO substrate . The symmetric supercapacitors were assembled by using two α-MnO2 nanorods working electrodes with a separator (Whatman, Grade GF/C) and 1M Na2SO4 aqueous electrolyte.
1.5 Characterization XRD patterns of the α-MnO2 nanorods and working electrode were recorded using Bruker AXSD8 Advance diffractometer. The morphologies and chemical composition of the samples were characterized by FE-SEM (Carl Zeiss, Ultra plus), TEM (FEI TECNAI G2), XPS (Perkin Elmer model 1257) and Raman spectroscopy (Renishaw, United Kingdom). Surface area of α-MnO2 nanorods was determined by BET principle and the pore parameters by BJH method using surface area analyzer (Quantachrome, USA at 77K). 1.6 Electrochemical characterization Cyclic voltammetry were measured in a voltage range of 0-0.8 V at different scan rates using an electrochemical work station (CHI 660D). The GCD and EIS measurements were measured by Gamry instrument (Interface 1000). The charge/discharge cycles were measured within a voltage range of 0-1.3 V at different current densities to evaluate the specific capacitance and its retention at high current density. Three thousand cycles were performed to check the capacitance retention over GCD curves. EIS was observed from 10 mHz to 100 kHz.
FIGURE S1. (a) XRD pattern of α-MnO2 nanorods, and (b) Raman spectra of α-MnO2 nanorods.
FIGURE S2. (a) SEM image of α-MnO2 nanorods at 200 and 100 nm scale. (b) SEM image of α-MnO2 nanorods with diameter of 27 nm and average lengths of 1.5-2 μm. (c) EDX elemental mapping of α-MnO2 nanorods. (d) TEM image of α-MnO2 nanorods. (e) High resolution TEM image of α-MnO2 nanorods. (f) SAED pattern of α-MnO2 nanorods.
FIGURE S3. (a) Nitrogen adsorption-desorption isotherms of α-MnO2 nanorods. (b) Pore size distributions of the α-MnO2 nanorods.
FIGURE S4. XPS spectra of α-MnO2/Ag/AAO working electrode (a) full spectra and, (b) Ag 3d.
FIGURE S5. CV curve of Ag/AAO current collector and α-MnO2/Ag/AAO working electrode at scan rate of 50 mV/s.
FIGURE S6. CV curve of symmetric supercapacitor device measured at different potential window at a scan rate of 50 mV/s.
FIGURE S7. (a) GCD curves for few initial and final cycles of symmetric device at 2 mA/cm2 current density. (b) CV curves of the symmetric device after charge/discharge cycles at a scan rate of 50 mV/s.
FIGURE S8. (a) SEM image of α-MnO2/Ag/AAO working electrode after 3000 cycles. (b) EDX spectra and, (c) EDX elemental mapping.
Table S1. Comparison of surface area of our MnO2 with previously reported nanostructures produced by different synthetic routes. Methoda
Plate like nanorods
Solution phase assembly
Chemical bath deposition
α-MnO2 urchin like
Simple chemical reaction
γ-MnO2 hollow structure
Facile one step method
(a) Different synthesis methods for supercapacitors electrode. (b) Different active material morphology. (c) BET surface area m2/g.
Table S2. Comparison of electrochemical performance of our MnO2 nanorods electrode with previously reported nanostructures using standard three-electrode cell.
(a) Different synthesis methods for MnO2 based electrode. (b) Different morphology of MnO2 based active material. (c) Specific capacitance in F/g. (d) Scan rate in mV/s. (e) Current densities in A/g.
Table S3. Comparison of specific capacitances and energy density of the reported MnO2/graphene and MnO2/other carbon nanomaterials composite-based electrodes.
235 (20 mV/s)
MnO2 nanowires/graphene (Asymmetric)
MnO2 thin film/carbon nanofibers
MnO2 nanorods on Ag/AAO
132 (0.5 mA/cm2)
(a) MnO2 based active material deposited on different current collectors. (b) Specific capacitance in F/g with respect to different current densities and scan rates. (c) Energy density in Wh/kg.
Table S4. Various performance parameters of the symmetric supercapacitor of the present work.
(a) Current density in A/g. (b) Discharge time in seconds. (c) Specific capacitance in F/g. (d) Specific energy in Wh/Kg. (e) Specific power in kW/Kg.
Table S5. The energy density and power density based on mass of fully packaged cell device. EDa
(a) Energy density in Wh/kg. (b) Power density in W/kg.
4. Calculations: 1. Calculation of active material mass on as-deposited Ag-AAO current collector (size = 6.15 cm2) Weight of Ag/AAO current collector = 0.7548 gm Weight of α-MnO2/Ag/AAO working electrode = 0.7564 gm Weight of active material (area 6.15 cm2) = 1.6 mg 2. Calculation of active material mass on working electrode (size = 1 cm2) Density of deposited mass ρ =
𝑚𝑎𝑠𝑠 𝑎𝑟𝑒𝑎 × 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
1.6 10−3 6.15 ×984 × 10−7
= 2.6 gm/cm3
Active material weight on working electrode (area = 1 cm2) = ρ× 𝑎𝑟𝑒𝑎 × 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 = 2.6× 1 × 984 × 10−7 m = 0.2658 mg 3. Calculation of total mass of fully packaged one symmetric supercapacitor device Weight of electrode (MnO2 + Ag/AAO) = 11.3 mg Weight of separator = 7.2 mg Weight of electrolyte = 3.2 mg Total mass of symmetric cell device = 2 (11.3 + 7.2 +3.2) = 32 mg 4. Capacitance calculation of electrode
The areal capacitance (Ca) and specific capacitance (Cs) of the electrode could be calculated from their cyclic curve by the following equations
∫−𝑉 𝐼(𝑉)𝑑𝑉 𝑚𝑣𝛥𝑉
∫−𝑉 𝐼(𝑉)𝑑𝑉 𝑆 𝑣 𝛥𝑉
Where Cs (in F/g) is the specific capacitance of the three-electrode cell, 𝑄 (in coulomb, C) is the total charge obtained by integrating the positive and negative sweeps in a CV curve, m (in grams, g) is the mass of the active materials electrodes (if the area Ca (mF/cm2) is more important for specific applications can be substituted by the electrode area), 𝑣 (in V/s) is the scan rate, and V=V+ ̶ V-, is the potential window between the positive (V+) and negative (V-) electrodes. 5. Calculation of capacitance, energy density and power density for symmetric supercapacitor cell The areal capacitance (Ca) and specific capacitance (Cs) of the symmetric supercapacitor device were calculated from cyclic voltammograms according to equation 𝑉
4 ∫−𝑉 𝐼(𝑉)𝑑𝑉 𝑆 𝑣 𝛥𝑉
4 ∫−𝑉 𝐼(𝑉)𝑑𝑉 𝑚 𝑣 𝛥𝑉
where S is the total geometrical area of the thin film electrodes in symmetric testing cell (11 cm2), 𝑣 is the scan rates (V/s), ΔV is the working potential window, I(V) is the response current during discharge. If the area replaced by mass of two electrodes the specific capacitance Cs (F/g). The specific capacitance (Cs) and areal capacitance (Ca) of the symmetric supercapacitor device were calculated from their charge-discharge curves according to the following equations 𝐶𝑠 =
where I is the discharge current, ∆t (=T2-T1) is the discharge time (corresponding to Vmax to 0), ∆V (=Vmax0) is the potential window during the discharge process removed the IR drop, m is the total mass of active materials of the two electrode, S is the effective area of the cell. For the symmetric device, the energy and power densities were calculated according to the following relations: 𝐶 𝑉2
𝐸𝐷 = 23.6(2𝑚) 𝑃𝐷 =
𝐸𝐷 3600 𝑇𝑠
where V is the voltage drop in the near-linear portion of the discharge curve after the IR drop (i.e. attainable cell voltage); m is the mass of active material on one electrode; C is the total capacitance measured from the two-electrode system; and Ts is the discharge time. 6. Supporting information video: After charging at 1 mA for 40 s, the device consisting of three supercapacitors units of area (11 cm2) could light the light emitting diode (LED) for over 5 min.
5. Supplementary References:     
       
           
W. Lee, S.-J. Park, Chem. Rev. 2014, 114, 7487-7556. A. Sanger, A. Kumar, S. Chauhan, Y. K. Gautam, R. Chandra, Sens. Actuator B-Chem. 2015, 213, 252-260. H. Zhao, C. Wang, R. Vellacheri, M. Zhou, Y. Xu, Q. Fu, M. Wu, F. Grote, Y. Lei, Adv. Mater. 2014, 26, 7654-7659. K. Wong-ek, P. Eiamchai, M. Horprathum, V. Patthanasettakul, P. Limnonthakul, P. Chindaudom, N. Nuntawong, Thin Solid Films 2010, 518, 7128-7132. a) W. Gao, N. Singh, L. Song, Z. Liu, A. L. M. Reddy, L. Ci, R. Vajtai, Q. Zhang, B. Wei, P. M. Ajayan, Nat. Nano 2011, 6, 496-500; b) D. Yang, J. Power Sources 2011, 196, 88438849. Z. K. Ghouri, M. Shaheer Akhtar, A. Zahoor, N. A. M. Barakat, W. Han, M. Park, B. Pant, P. S. Saud, C. H. Lee, H. Y. Kim, J. Alloys Compd. 2015, 642, 210-215. V. Subramanian, H. Zhu, R. Vajtai, P. M. Ajayan, B. Wei, J. Phys. Chem. B 2005, 109, 20207-20214. T. H. Mahato, G. K. Prasad, B. Singh, K. Batra, K. Ganesan, Microporous Mesoporous Mater. 2010, 132, 15-21. L. Deng, G. Zhu, J. Wang, L. Kang, Z.-H. Liu, Z. Yang, Z. Wang, J. Power Sources 2011, 196, 10782-10787. D. P. Dubal, D. Aradilla, G. Bidan, P. Gentile, T. J. S. Schubert, J. Wimberg, S. Sadki, P. Gomez-Romero, Sci. Rep. 2015, 5, 9771. K.-N. Jung, A. Riaz, S.-B. Lee, T.-H. Lim, S.-J. Park, R.-H. Song, S. Yoon, K.-H. Shin, J.W. Lee, J. Power Sources 2013, 244, 328-335. F. Xiaobo, F. Jiyun, W. Huan, N. Ka Ming, Nanotechnology 2009, 20, 375601. R. Ranjusha, A. Sreekumaran Nair, S. Ramakrishna, P. Anjali, K. Sujith, K. R. V. Subramanian, N. Sivakumar, T. N. Kim, S. V. Nair, A. Balakrishnan, J. Mater. Chem. 2012, 22, 20465-20471. G. Zhao, J. Li, X. Ren, J. Hu, W. Hu, X. Wang, RSC Adv. 2013, 3, 12909-12914. Y. Ma, R. Wang, H. Wang, J. Key, S. Ji, J. Power Sources 2015, 280, 526-532. M. N. Patel, X. Wang, B. Wilson, D. A. Ferrer, S. Dai, K. J. Stevenson, K. P. Johnston, J. Mater. Chem. 2010, 20, 390-398. C.-L. Ho, M.-S. Wu, The J. Phys. Chem. C 2011, 115, 22068-22074. D. Liu, Q. Wang, L. Qiao, F. Li, D. Wang, Z. Yang, D. He, J. Mater. Chem. 2012, 22, 483487. S. Dong, X. Chen, L. Gu, X. Zhou, L. Li, Z. Liu, P. Han, H. Xu, J. Yao, H. Wang, X. Zhang, C. Shang, G. Cui, L. Chen, Energy Environ Sci . 2011, 4, 3502-3508. P. Lv, P. Zhang, Y. Feng, Y. Li, W. Feng, Electrochim. Acta 2012, 78, 515-523. Q. Li, X.-F. Lu, H. Xu, Y.-X. Tong, G.-R. Li, ACS Appl. Mater. Interfaces 2014, 6, 27262733. S. F. Chin, S. C. Pang, Mater. Chem. Phys. 2010, 124, 29-32. Z. Sun, S. Firdoz, E. Ying-Xuan Yap, L. Li, X. Lu, Nanoscale 2013, 5, 4379-4387. X. Feng, Z. Yan, N. Chen, Y. Zhang, Y. Ma, X. Liu, Q. Fan, L. Wang, W. Huang, J. Mater. Chem. A 2013, 1, 12818-12825. Q. Cheng, J. Tang, J. Ma, H. Zhang, N. Shinya, L.-C. Qin, Carbon 2011, 49, 2917-2925.
     
R. B. Rakhi, W. Chen, D. Cha, H. N. Alshareef, Journal of Materials Chemistry 2011, 21, 16197-16204. Z.-S. Wu, W. Ren, D.-W. Wang, F. Li, B. Liu, H.-M. Cheng, ACS Nano 2010, 4, 58355842. J. Liu, J. Essner, J. Li, Chemistry of Materials 2010, 22, 5022-5030. L. Peng, X. Peng, B. Liu, C. Wu, Y. Xie, G. Yu, Nano Letters 2013, 13, 2151-2157. C.-Y. Chen, C.-Y. Fan, M.-T. Lee, J.-K. Chang, Journal of Materials Chemistry 2012, 22, 7697-7700. G. Yu, L. Hu, M. Vosgueritchian, H. Wang, X. Xie, J. R. McDonough, X. Cui, Y. Cui, Z. Bao, Nano Letters 2011, 11, 2905-2911.