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Synthesis and electrochemical properties of multilayered porous hexagonal Mn(OH)2 nanoplates as supercapacitor electrode material
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Synthesis and electrochemical properties of multilayered porous hexagonal Mn(OH)2 nanoplates as supercapacitor electrode material De Yan, Yanhong Li, Ying Liu, Renfu Zhuo, Zhiguo Wu, Baisong Geng, Jun Wang, Pingyuang Ren, Pengxun Yan, Zhongrong Geng
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(14)01466-9 http://dx.doi.org/10.1016/j.matlet.2014.08.010 MLBLUE17530
To appear in:
Materials Letters
Received date: 14 May 2014 Accepted date: 2 August 2014 Cite this article as: De Yan, Yanhong Li, Ying Liu, Renfu Zhuo, Zhiguo Wu, Baisong Geng, Jun Wang, Pingyuang Ren, Pengxun Yan, Zhongrong Geng, Synthesis and electrochemical properties of multilayered porous hexagonal Mn(OH)2 nanoplates as supercapacitor electrode material, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2014.08.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis and electrochemical properties of multilayered porous hexagonal Mn(OH)2 nanoplates as supercapacitor electrode material De Yan a, *, Yanhong Li a, Ying Liu a, Renfu Zhuo a, Zhiguo Wu a, Baisong Geng a, Jun Wang a, Pingyuang Ren a, Pengxun Yan a, b, Zhongrong Geng c a
b
School of Physical Science and Technology, Lanzhou University, 730000, China Key Laboratory of Solid Lubrication, Institute of Chemistry and Physics, Chinese
Academy of Science, Lanzhou, 730000, China c
School of Mechatronic Engineering, Lanzhou Jiaotong University, Lanzhou 730070,
China * Corresponding author. Tel: +86-931-8912719; Fax: +86-931-8913554; E-mail: [email protected]. (De Yan)
Abstract: Hexagonal Mn(OH)2 nanoplates with thickness of about 20 nm were synthesized by a simple hydrothermal method. Each nanoplate consists of several porous nanosheets and the pores in nanosheets are of about 10nm. Electrochemical tests reveal that the as-prepared multilayered porous Mn(OH)2 nanoplate has a capacitance of 147.4 F/g at 0.1 A/g, good rate capability of 21.6 F/g even at a high current density of 10 A/g. These porous nanoplates also show excellent cycle stability with capacitance retention of 86.3% after 5000 cycles at a relative high current density of 5A/g. The excellent performance of the sample can be attributed to its multilayered porous structure. This material has great potential application in supercapacitor electrode material, especially where long cycle life and excellent cycle stability are required. Key words: energy storage and conversion; porous materials; nanocrystalline materials 1
1. Introduction Recently, supercapacitor electrode material [1], such as the oxides of Mn, Ni, Co and V, has attracted great attention because of the wide application of supercapacitor. Manganese oxides/hydroxides [2, 3] were among the most promising electrode materials because of their low cost, environmental friendliness, and excellent capacitive performance in aqueous electrolytes [4-6]. Among them, δ-MnO2 with a layered structure is extensively studied because of its high theoretical specific capacitance, but the poor cycle stability caused by Jahn-Teller effect [7] and the poor conductivity [8] greatly hindered its application. Mn(OH)2 has a layered crystal structure with interlayer spacing is 0.47nm. This particular structure, which is similar to δ-MnO2, can not only accommodate large number of ions but also greatly facilitate the diffusion of ions in it. So it is deduced that Mn(OH)2 may also have good supercapacitive property. However, among the few reports referred to Mn(OH)2, it is often used as an intermediate to prepare Mn2O3 [9, 10]. Liu et al. [11] prepared Mn(OH)2 nanoparticles on multi-walled carbon nanotube and the composite material shows a high specific capacitance of 297.5 F/g calculated by CV curve at a scan rate of 20 mV/s, but they did not show the supercapacitive property of sole Mn(OH)2. To the best of our knowledge, the supercapacitive study on sole Mn(OH)2 is not previously reported and the supercapacitive property of their composite material is also rarely seen in literature. Here, we report the hydrothermal preparation and supercapacitive property of multilayered porous hexagonal Mn(OH)2 nanoplates. The relation between its structure, 2
morphology and supercapacitive property were also discussed. 2. Experiment 200 mg KMnO4, 200 mg NaOH and 200 mg glucose were dissolved in deionized water with total volume 30 mL. After stirring, the solution was transferred into an autoclave and heated at 200 °C for 72 h. Then cool down to room temperature naturally. The product was repeatedly washed with deionized water and ethanol, and then dried at 80°C for 10 h. The product was characterized by X-ray diffraction (XRD, a Philips X’ Pert Pro. Diffractometer), field emission scanning electron microscopy (FESEM, JSM -6701F) and transmission electron microscope (TEM, Tecnai-G2-F30). Electrochemical tests were performed on an electrochemical workstation (CHI 660E) in 1M Na2SO4 solution in a three-electrode system. The working electrode was fabricated by mixing the product: acetylene black: polytetrafluorene -ethylene (PTFE) at a mass ratio of 90:5:5. The mixture was pressed onto nickel foam and dried at 80 °C overnight. The mass loading is about 2.9 mg. 3. Results and discussion All peaks in XRD pattern (Fig. 1(a)) of the sample can be well indexed to hexagonal Mn(OH)2 (pyrochroite, JCPDS No. 73-1604). The hexagonal Mn(OH)2 is a layered brucite crystal, each layer comprises edge-sharing Mn(II)(OH)6 octahedron and neighboring layers are bound together by van der Waal forces [9, 10]. FESEM image (Fig. 1(b)) of the sample reveal that the sample is hexagonal nanoplates with thickness of about 20 nm and lateral dimension of about several hundreds of nanometers to several microns. TEM images (Fig. 1(c)) reveal that the hexagonal nanoplate is actually 3
porous, and the plate is composed of several nanosheets seen form the lateral part of the plate. HRTEM image (Fig. 1(d)) clearly reveals that the pore size in the stacked nanosheets is about 10nm. The important point is not the pore size but its mesoporous nature which can greatly facilitate the ion diffusion in it, so the nitrogen adsorption method is not employed. The d-spacing of 0.49nm shown in the inset of Fig. 1(d) corresponds to the (001) plane of Mn(OH)2 with a little lattice expansion. Cyclic voltammetry (CV) curves of the sample in 1 M Na2SO4 electrolyte at 5, 50 and 200 mV/s were shown in Fig. 2(a). The CV curve shows little deviation from rectangular shape at 5 mV/s, indicating the existence of pseudocapacitance. The deviation becomes obvious with increasing voltage scan rate. This can be ascribed to the change of ion transplant surrounding, for which the ions can only reach the outer surface of the electrode and not enter into the interior pores at a large scan rate [12, 13]. Galvanostatic charging/discharging (GCD) curves at various current densities were shown in Fig. 2 (b) and (c). The charge and discharge curve shows little deviation from symmetric variation of the voltage at 0.1 A/g. With the current density increasing, the deviation becomes obvious, which can be attributed to the polarization of the electrode. Specific capacitance at different current densities was calculated from the discharge plot of the GCD curve. A high specific capacitance of 147.4 F/g was obtained at 0.1A/g, which is higher than sole δ-MnO2 of 110 F/g [5] reported by Wei et al., and this performance can be greatly promoted by combining with carbonaceous material, such as CNT [11] and graphene [14]. Therefore, Mn(OH)2 is also a promising supercapacitor electrode material. The specific capacitance is 137.7, 131.8, 116.1, 95, 84.3, 70, 57.3, 4
48.9, 41.2, 34.4, 26.7 and 21.6 F/g at 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 A/g, respectively. The decrease of specific capacitance with increasing current density can be explained by an increased internal polarization at higher current densities [15, 16]. An endurance test was conducted using GCD cycles (Fig. 2(e)) to investigate the cycling stability of the product. Result shows that the capacitance retention reaches 86.3% after 5000 cycles at a current density of 5A/g in the potential range of 0-1V (vs. SCE). This reveals the excellent cycle stability of hexagonal multilayered porous Mn(OH)2 . Electrochemical impedance spectroscopy (EIS) measurements were carried out from 100 kHz to 0.01 Hz at open circuit potential with an ac perturbation of 5 mV, and the results are shown in Fig. 3(a). The EIS curves were analyzed using the complex nonlinear least-squares (CNLS) fitting method on the basis of the equivalent circuit, which is given in the inset of Fig. 3(a). The high frequency intercept on the real impedance axis yields the electrolyte resistance Rs, the diameter of the semi-circle gives an indication of the charge transfer resistance Rct, Cdl is the double-layer capacitance of the grain surface, CL is the limit capacitance [17], Q1 and Q2 are the constant phase angle elements relates to the pseudocapacitance. Two EIS curves in Fig. 3(a) show almost the same profile, which means the electrochemical kinetics of the system does not have an obvious change after 5000 cycles. The increase of the diameter of the semicircle indicates the increase of the charge transfer resisitance Rct, which may be caused by the decrease of effective contact between the active electrode material and the current collector caused by the morphology change (Fig. 3(b)) and phase change during cycling. The follower-like morphology and the nanosheet array vertically grew on the 5
surface of the plate are the typical morphology of δ-MnO2. The excellent electrochemical properties of Mn(OH)2 can be attributed to its unique structure. Firstly, the as-prepared Mn(OH)2 hexagonal nanoplate has a layered crystal structure with interlayer spacing of 0.49nm, which can not only accommodate a large number of ions but also facilitate the ion diffusion in it. Secondly, the nanoplate is composed of several stacked nanosheets and the space between these sheets can also accommodate ions. These may greatly contribute to the specific capacitance and rate capability of the sample. Thirdly, each of the stacked nanosheet is porous with pores of about 10nm. These pores can greatly increase the electrode/electrolyte interface, facilitate ion diffusion and shorten the diffusion path of ions in the electrode, and thus make contribution to the rate capability and cycle stability of the electrode. Therefore, the multilayered porous Mn(OH)2 hexagonal nanoplates exhibit high specific capacitance, good rate capability, long cycle life and excellent cycle stability. 4. Conclusions Multilayered porous hexagonal Mn(OH)2 nanoplates were synthesized by a simple hydrothermal method. The sample exhibits a specific capacitance of 147.4 F/g at a current density of 0.1 A/g, good rate capability of 21.6 F/g even at a high current density of 10 A/g, and long cycle life and excellent cycle stability with capacitance retention of 86.3% after 5000 cycles at a relative high current density of 5A/g. The excellent performance of Mn(OH)2 was attributed to its unique multilayered porous structure, which can greatly increase the electrode/electrolyte interface, facilitate ion diffusion and shorten the ion diffusion path. 6
Acknowledgement This work is supported by the National Natural Science Foundation of China (Grant NO. 11204114 and Grant NO. 11104126). References [1] Miller JR, Simon P, Science 321 (2008) 651-652. [2] Liu Y, Yan D, Zhuo RF, et al. J Power Sources 242 (2013) 78-85. [3] Yan D, Li YH, Liu Y, et al. Mater Lett 117 (2014) 62- 65. [4] Yan J, Wei T, Cheng J, et al. Mater Res Bull 45 (2010) 210-215. [5] Wei WF, Cui XW, Chen WX, et al. Chem Soc Rev 40 (2011) 1679-1721. [6] Crossa A, Morelb A, Cormiea A, et al. J Power Sources 196 (2011) 7847-7853. [7] Mendiboure A, Delmas C, Hagenmuller P, J Solid State Chem 57 (1985) 323-331. [8] Toupin M, Brousse T, Belanger D, Chem Mater 16 (2004) 3184-3190. [9] Zhang X, Xing Z, Wang LL, et al. J Mater Chem 22 (2012) 17864-17869 [10] Zhang X, Qian YT, Zhu YC, et al. Nanoscale, 6 (2014) 1725-1731 [11] Liu JM, Hu Y, Chuang TL, et al. Thin Solid Films 544 (2013) 186-190. [12] Pech D, Brunet M, Durou H, et al. Nat Nanotechnol 5 (2010) 651-654. [13] Lang XY, Hirata A, Fujita T, et al. Nat Nanotechnol 6 (2011) 232-236. [14] Liu Y, Yan D, Zhuo RF, et al. J Power Sources 242 (2013) 78-85. [15] Niu JJ, Pell WG, Conway BE, J Power Sources 156 (2006) 725-740. [16] Mi HY, Zhang XG, Ye XG, et al. J Power Sources 176 (2008) 403-409. [17] Wu MS, Huang CY, Lin KH, J Power Sources 186 (2009) 557-564.
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Figures and captions: Fig. 1. (a) XRD pattern, (b) FESEM image, and (c)-(d) TEM and HRTEM images of the sample. Fig. 2. (a) CV curve, (b)-(c) GCD curves of the electrode. (d) Specific capacitance at different current densities calculated from the discharge plot. (e) Plot of capacitance retention vs. cycle number. Fig. 3. (a) EIS curve of the electrode before and after 5000 cycles, and the corresponding equivalent circuit, (b) FESEM image of the sample after cycling.
Fig. 1.
Fig. 2.
8
Fig. 3. ¾ Multilayered porous hexagonal Mn(OH)2 nanoplates were synthesized. ¾ Mn(OH)2 nanoplates exhibit a specific capacitance of 147.4 F/g at 0.1 A/g. ¾ Capacitance retention reaches 86.3% after 5000 cycles at 5 A/g. ¾ The excellent cycle stability can be ascribed to its multilayered porous structure.
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Synthesis and electrochemical properties of multilayered porous hexagonal Mn(OH)2 nanoplates as supercapacitor electrode material De Yan, Yanhong Li, Ying Liu, Renfu Zhuo, Zhiguo Wu, Baisong Geng, Jun Wang, Pingyuang Ren, Pengxun Yan, Zhongrong Geng
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(14)01466-9 http://dx.doi.org/10.1016/j.matlet.2014.08.010 MLBLUE17530
To appear in:
Materials Letters
Received date: 14 May 2014 Accepted date: 2 August 2014 Cite this article as: De Yan, Yanhong Li, Ying Liu, Renfu Zhuo, Zhiguo Wu, Baisong Geng, Jun Wang, Pingyuang Ren, Pengxun Yan, Zhongrong Geng, Synthesis and electrochemical properties of multilayered porous hexagonal Mn(OH)2 nanoplates as supercapacitor electrode material, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2014.08.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis and electrochemical properties of multilayered porous hexagonal Mn(OH)2 nanoplates as supercapacitor electrode material De Yan a, *, Yanhong Li a, Ying Liu a, Renfu Zhuo a, Zhiguo Wu a, Baisong Geng a, Jun Wang a, Pingyuang Ren a, Pengxun Yan a, b, Zhongrong Geng c a
b
School of Physical Science and Technology, Lanzhou University, 730000, China Key Laboratory of Solid Lubrication, Institute of Chemistry and Physics, Chinese
Academy of Science, Lanzhou, 730000, China c
School of Mechatronic Engineering, Lanzhou Jiaotong University, Lanzhou 730070,
China * Corresponding author. Tel: +86-931-8912719; Fax: +86-931-8913554; E-mail: [email protected]. (De Yan)
Abstract: Hexagonal Mn(OH)2 nanoplates with thickness of about 20 nm were synthesized by a simple hydrothermal method. Each nanoplate consists of several porous nanosheets and the pores in nanosheets are of about 10nm. Electrochemical tests reveal that the as-prepared multilayered porous Mn(OH)2 nanoplate has a capacitance of 147.4 F/g at 0.1 A/g, good rate capability of 21.6 F/g even at a high current density of 10 A/g. These porous nanoplates also show excellent cycle stability with capacitance retention of 86.3% after 5000 cycles at a relative high current density of 5A/g. The excellent performance of the sample can be attributed to its multilayered porous structure. This material has great potential application in supercapacitor electrode material, especially where long cycle life and excellent cycle stability are required. Key words: energy storage and conversion; porous materials; nanocrystalline materials 1
1. Introduction Recently, supercapacitor electrode material [1], such as the oxides of Mn, Ni, Co and V, has attracted great attention because of the wide application of supercapacitor. Manganese oxides/hydroxides [2, 3] were among the most promising electrode materials because of their low cost, environmental friendliness, and excellent capacitive performance in aqueous electrolytes [4-6]. Among them, δ-MnO2 with a layered structure is extensively studied because of its high theoretical specific capacitance, but the poor cycle stability caused by Jahn-Teller effect [7] and the poor conductivity [8] greatly hindered its application. Mn(OH)2 has a layered crystal structure with interlayer spacing is 0.47nm. This particular structure, which is similar to δ-MnO2, can not only accommodate large number of ions but also greatly facilitate the diffusion of ions in it. So it is deduced that Mn(OH)2 may also have good supercapacitive property. However, among the few reports referred to Mn(OH)2, it is often used as an intermediate to prepare Mn2O3 [9, 10]. Liu et al. [11] prepared Mn(OH)2 nanoparticles on multi-walled carbon nanotube and the composite material shows a high specific capacitance of 297.5 F/g calculated by CV curve at a scan rate of 20 mV/s, but they did not show the supercapacitive property of sole Mn(OH)2. To the best of our knowledge, the supercapacitive study on sole Mn(OH)2 is not previously reported and the supercapacitive property of their composite material is also rarely seen in literature. Here, we report the hydrothermal preparation and supercapacitive property of multilayered porous hexagonal Mn(OH)2 nanoplates. The relation between its structure, 2
morphology and supercapacitive property were also discussed. 2. Experiment 200 mg KMnO4, 200 mg NaOH and 200 mg glucose were dissolved in deionized water with total volume 30 mL. After stirring, the solution was transferred into an autoclave and heated at 200 °C for 72 h. Then cool down to room temperature naturally. The product was repeatedly washed with deionized water and ethanol, and then dried at 80°C for 10 h. The product was characterized by X-ray diffraction (XRD, a Philips X’ Pert Pro. Diffractometer), field emission scanning electron microscopy (FESEM, JSM -6701F) and transmission electron microscope (TEM, Tecnai-G2-F30). Electrochemical tests were performed on an electrochemical workstation (CHI 660E) in 1M Na2SO4 solution in a three-electrode system. The working electrode was fabricated by mixing the product: acetylene black: polytetrafluorene -ethylene (PTFE) at a mass ratio of 90:5:5. The mixture was pressed onto nickel foam and dried at 80 °C overnight. The mass loading is about 2.9 mg. 3. Results and discussion All peaks in XRD pattern (Fig. 1(a)) of the sample can be well indexed to hexagonal Mn(OH)2 (pyrochroite, JCPDS No. 73-1604). The hexagonal Mn(OH)2 is a layered brucite crystal, each layer comprises edge-sharing Mn(II)(OH)6 octahedron and neighboring layers are bound together by van der Waal forces [9, 10]. FESEM image (Fig. 1(b)) of the sample reveal that the sample is hexagonal nanoplates with thickness of about 20 nm and lateral dimension of about several hundreds of nanometers to several microns. TEM images (Fig. 1(c)) reveal that the hexagonal nanoplate is actually 3
porous, and the plate is composed of several nanosheets seen form the lateral part of the plate. HRTEM image (Fig. 1(d)) clearly reveals that the pore size in the stacked nanosheets is about 10nm. The important point is not the pore size but its mesoporous nature which can greatly facilitate the ion diffusion in it, so the nitrogen adsorption method is not employed. The d-spacing of 0.49nm shown in the inset of Fig. 1(d) corresponds to the (001) plane of Mn(OH)2 with a little lattice expansion. Cyclic voltammetry (CV) curves of the sample in 1 M Na2SO4 electrolyte at 5, 50 and 200 mV/s were shown in Fig. 2(a). The CV curve shows little deviation from rectangular shape at 5 mV/s, indicating the existence of pseudocapacitance. The deviation becomes obvious with increasing voltage scan rate. This can be ascribed to the change of ion transplant surrounding, for which the ions can only reach the outer surface of the electrode and not enter into the interior pores at a large scan rate [12, 13]. Galvanostatic charging/discharging (GCD) curves at various current densities were shown in Fig. 2 (b) and (c). The charge and discharge curve shows little deviation from symmetric variation of the voltage at 0.1 A/g. With the current density increasing, the deviation becomes obvious, which can be attributed to the polarization of the electrode. Specific capacitance at different current densities was calculated from the discharge plot of the GCD curve. A high specific capacitance of 147.4 F/g was obtained at 0.1A/g, which is higher than sole δ-MnO2 of 110 F/g [5] reported by Wei et al., and this performance can be greatly promoted by combining with carbonaceous material, such as CNT [11] and graphene [14]. Therefore, Mn(OH)2 is also a promising supercapacitor electrode material. The specific capacitance is 137.7, 131.8, 116.1, 95, 84.3, 70, 57.3, 4
48.9, 41.2, 34.4, 26.7 and 21.6 F/g at 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 A/g, respectively. The decrease of specific capacitance with increasing current density can be explained by an increased internal polarization at higher current densities [15, 16]. An endurance test was conducted using GCD cycles (Fig. 2(e)) to investigate the cycling stability of the product. Result shows that the capacitance retention reaches 86.3% after 5000 cycles at a current density of 5A/g in the potential range of 0-1V (vs. SCE). This reveals the excellent cycle stability of hexagonal multilayered porous Mn(OH)2 . Electrochemical impedance spectroscopy (EIS) measurements were carried out from 100 kHz to 0.01 Hz at open circuit potential with an ac perturbation of 5 mV, and the results are shown in Fig. 3(a). The EIS curves were analyzed using the complex nonlinear least-squares (CNLS) fitting method on the basis of the equivalent circuit, which is given in the inset of Fig. 3(a). The high frequency intercept on the real impedance axis yields the electrolyte resistance Rs, the diameter of the semi-circle gives an indication of the charge transfer resistance Rct, Cdl is the double-layer capacitance of the grain surface, CL is the limit capacitance [17], Q1 and Q2 are the constant phase angle elements relates to the pseudocapacitance. Two EIS curves in Fig. 3(a) show almost the same profile, which means the electrochemical kinetics of the system does not have an obvious change after 5000 cycles. The increase of the diameter of the semicircle indicates the increase of the charge transfer resisitance Rct, which may be caused by the decrease of effective contact between the active electrode material and the current collector caused by the morphology change (Fig. 3(b)) and phase change during cycling. The follower-like morphology and the nanosheet array vertically grew on the 5
surface of the plate are the typical morphology of δ-MnO2. The excellent electrochemical properties of Mn(OH)2 can be attributed to its unique structure. Firstly, the as-prepared Mn(OH)2 hexagonal nanoplate has a layered crystal structure with interlayer spacing of 0.49nm, which can not only accommodate a large number of ions but also facilitate the ion diffusion in it. Secondly, the nanoplate is composed of several stacked nanosheets and the space between these sheets can also accommodate ions. These may greatly contribute to the specific capacitance and rate capability of the sample. Thirdly, each of the stacked nanosheet is porous with pores of about 10nm. These pores can greatly increase the electrode/electrolyte interface, facilitate ion diffusion and shorten the diffusion path of ions in the electrode, and thus make contribution to the rate capability and cycle stability of the electrode. Therefore, the multilayered porous Mn(OH)2 hexagonal nanoplates exhibit high specific capacitance, good rate capability, long cycle life and excellent cycle stability. 4. Conclusions Multilayered porous hexagonal Mn(OH)2 nanoplates were synthesized by a simple hydrothermal method. The sample exhibits a specific capacitance of 147.4 F/g at a current density of 0.1 A/g, good rate capability of 21.6 F/g even at a high current density of 10 A/g, and long cycle life and excellent cycle stability with capacitance retention of 86.3% after 5000 cycles at a relative high current density of 5A/g. The excellent performance of Mn(OH)2 was attributed to its unique multilayered porous structure, which can greatly increase the electrode/electrolyte interface, facilitate ion diffusion and shorten the ion diffusion path. 6
Acknowledgement This work is supported by the National Natural Science Foundation of China (Grant NO. 11204114 and Grant NO. 11104126). References [1] Miller JR, Simon P, Science 321 (2008) 651-652. [2] Liu Y, Yan D, Zhuo RF, et al. J Power Sources 242 (2013) 78-85. [3] Yan D, Li YH, Liu Y, et al. Mater Lett 117 (2014) 62- 65. [4] Yan J, Wei T, Cheng J, et al. Mater Res Bull 45 (2010) 210-215. [5] Wei WF, Cui XW, Chen WX, et al. Chem Soc Rev 40 (2011) 1679-1721. [6] Crossa A, Morelb A, Cormiea A, et al. J Power Sources 196 (2011) 7847-7853. [7] Mendiboure A, Delmas C, Hagenmuller P, J Solid State Chem 57 (1985) 323-331. [8] Toupin M, Brousse T, Belanger D, Chem Mater 16 (2004) 3184-3190. [9] Zhang X, Xing Z, Wang LL, et al. J Mater Chem 22 (2012) 17864-17869 [10] Zhang X, Qian YT, Zhu YC, et al. Nanoscale, 6 (2014) 1725-1731 [11] Liu JM, Hu Y, Chuang TL, et al. Thin Solid Films 544 (2013) 186-190. [12] Pech D, Brunet M, Durou H, et al. Nat Nanotechnol 5 (2010) 651-654. [13] Lang XY, Hirata A, Fujita T, et al. Nat Nanotechnol 6 (2011) 232-236. [14] Liu Y, Yan D, Zhuo RF, et al. J Power Sources 242 (2013) 78-85. [15] Niu JJ, Pell WG, Conway BE, J Power Sources 156 (2006) 725-740. [16] Mi HY, Zhang XG, Ye XG, et al. J Power Sources 176 (2008) 403-409. [17] Wu MS, Huang CY, Lin KH, J Power Sources 186 (2009) 557-564.
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Figures and captions: Fig. 1. (a) XRD pattern, (b) FESEM image, and (c)-(d) TEM and HRTEM images of the sample. Fig. 2. (a) CV curve, (b)-(c) GCD curves of the electrode. (d) Specific capacitance at different current densities calculated from the discharge plot. (e) Plot of capacitance retention vs. cycle number. Fig. 3. (a) EIS curve of the electrode before and after 5000 cycles, and the corresponding equivalent circuit, (b) FESEM image of the sample after cycling.
Fig. 1.
Fig. 2.
8
Fig. 3. ¾ Multilayered porous hexagonal Mn(OH)2 nanoplates were synthesized. ¾ Mn(OH)2 nanoplates exhibit a specific capacitance of 147.4 F/g at 0.1 A/g. ¾ Capacitance retention reaches 86.3% after 5000 cycles at 5 A/g. ¾ The excellent cycle stability can be ascribed to its multilayered porous structure.
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