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Biotemplate assisted synthesis of 3D hierarchical porous NiO for supercapatior application with excellent rate performance
Materials Letters 128 (2014) 117–120
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Biotemplate assisted synthesis of 3D hierarchical porous NiO for supercapatior application with excellent rate performance Jing He a, Yufeng Zhao a,n, Ding-Bang Xiong b, Wei Ran a, Jiang Xu a, Yuqin Ren c, Long Zhang a, Yongfu Tang a, Faming Gao a a
Key Laboratory of Applied Chemistry, Yanshan University, Qinhuangdao 066004, China State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, Shanghai 200240, China c Beidaihe Center Experiment Station, Chinese Academy of Fishery Science, 066100 Beidaihe, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 23 January 2014 Accepted 22 April 2014 Available online 2 May 2014
A novel 3D hierarchical porous nickel oxide (NiO) was fabricated by a facile biotemplate assisted method. Physicochemical characterizations indicate that the as prepared hierarchical porous NiO is assembled by multiple-layered porous nanosheets, of which the pore structure is highly ordered. The electrochemical performance of the as prepared hierarchical porous NiO was carried out in 6 M KOH, exhibited relatively high specific capacitance value of 493 F g 1 at a current density of 0.3 A g 1, good rate performance ( 93% capacity retention from 0.3 A g 1 to 10 A g 1), as well as good cycling stability ( 96% retention upon 2000 charge/discharge cycles at 10 A g 1). & 2014 Elsevier B.V. All rights reserved.
Keywords: Hierarchical porous Nickel oxide Supercapacitor AFM Ceramics
1. Introduction Nickel oxide (NiO) is a promising electrode material for supercapacitors, owing to its high theoretical capacity ( 2584 F g 1 within 0.5 V), low cost, easy availability and relatively environmental friendliness [1–3]. However, the poor stability and rate performance, as well as much lower specific capacitance (SC) of NiO electrode than theoretical value, have seriously restricted their extensive applications [4,5]. It is widely reported that the electrochemical performance of NiO is notably related to its morphology and microstructure [6,7]. So far, nickel oxides with various nanostructures, such as nanosheets [8], nanotubes [9], nanospheres [10] and some nanoporous structures [11–15], have been successfully fabricated and used for the electrode materials of supercapacitors. In particular, NiO with three dimensional (3D) hierarchical porous nanostructures, which can normally provide high surface area, continuous electron pathway and fast ion transportation, has shown its unique advantages in improving the cycling stability, rate performance, as well as providing high SC value when used as an electrode for supercapacitors. Nevertheless, most researchers mainly focus on two-dimensional (2D) structured hierarchical porous film [12,13] or hierarchically porous spheres [14,15]. There is few research about the preparation and
n
Corresponding author. Tel.: þ 86 335 8387743. E-mail addresses: [email protected], [email protected] (Y. Zhao), [email protected] (Y. Tang). http://dx.doi.org/10.1016/j.matlet.2014.04.152 0167-577X/& 2014 Elsevier B.V. All rights reserved.
application of NiO with three-dimensional (3D) hierarchical porous structure for supercapacitors. Recently, great efforts have been devoted to synthesis hierarchical porous structure with a template-assisted method, remarkably, biotemplates (such as egg-shell [16], pinwood [17], pollen [18], bacteria [19], etc.) with precise sizes, uniform geometries and stable structure, have been used as producing materials with controllable complex morphologies and multiple porous structures. Previously, we have successfully synthesized hierarchical porous LiNiCuZn-oxides using Artemia cyst shells (AS) as hard template [20]. In this work, a novel 3D hierarchical porous NiO was synthesized by a facile biotemplate assisted method with AS as the hard template and poly(vinylpyrrolidone) (PVP) as the structure-directing agent. The as-prepared NiO successfully replicates the structure of natural Artemia cyst shell, and shows good capacitive performance.
2. Experimental The hierarchical porous NiO was synthesized through a biotemplate assisted method. To elaborate, 0.3 g of PVP and 0.6 g of nickel acetate tetrahydrate (Ni(CH3COOH)2 4H2O) were dissolved in 30 ml ethylene glycol (EG). 0.6 g of ball-milled shells, as the hard template, was added to the obtained solution. The mixture was stirred for 2 h and then kept in the vacuum oven for 6 h at room temperature. Then the as-prepared product was heated at
118
J. He et al. / Materials Letters 128 (2014) 117–120
80 1C for 12 h. Finally, hierarchical porous NiO was obtained after calcination in air at 500 1C for 6 h. The morphology of NiO samples was characterized by FESEM (Hitachi-S4800, 15 kV) and TEM (Hitachi-7650, 80 kV). Powder X-ray diffraction (XRD) patterns of NiO samples were recorded using an X-ray diffractometer (Rigaku, λ ¼1.5418 Å). The specific Brunauer–Emmett–Teller (BET) surface area and pore size distribution were measured using a Micromeritics ASAP2020 analyzer. The electrochemical measurements were carried out through a three-electrode electrochemical system in 6 M KOH electrolyte. Platinum foil, Hg/HgO (0.1 M KOH) and NiO active material coated nickel foam were used as the counterelectrode, reference electrode and working electrode, respectively. The working electrode was fabricated as follows. 80 wt% of as-prepared NiO sample, 15 wt% of acetylene carbon black and 5 wt% PTFE (polytetrafluoroethylene) were mixed to obtain homogeneous slurry. The obtained slurry was coated on a 1 1 cm2 area foam nickel substrate and dried in vacuum at 120 1C for 12 h. The active material loading of the electrode was 4.0 mg cm 2. Cyclic voltammetry (CV) and the electrochemical impedance spectra (EIS) were tested on a CHI660c electrochemical workstation (Chenhua, China). Galvanostatical charge–discharge test was conducted on a LAND battery program-control test system (Land, CT2001A, China).
3. Results and discussion The morphology and microstructure of Artemia cyst shells and the as prepared NiO are shown in Fig. 1. The original Artemia cyst shell is in spherical shape (Fig. 1a). After being ball milled into small pieces, the hierarchical porous structure of Artemia cyst shell is fully exposed (Fig. 1b). The Artemia cyst shell is mainly composed of macropores with diameters from 200 nm to 1 μm. FESEM image of the as-prepared NiO (Fig. 1c) shows that the 3D
hierarchical porous NiO is assembled by highly ordered macropores from 200 to 500 nm of which the structure is multi-layered and perfectly interconnected. And the pore wall is assembled by NiO nanoparticles from 20 to 75 nm (inset of Fig. 1d). The TEM image (Fig. 1d) confirms the hierarchical porous architecture of the as-prepared NiO, which indicates that the as-prepared hierarchical porous NiO has successfully replicated the original structure of Artemia cyst shells. The XRD patterns of the as-prepared product (Fig. 1e) indicate characteristic peaks of cubic NiO (space group Fm3m (225)), according to the standard card of JCPDS no. 47-1049. No impurities are observed. Fig. 2a shows the nitrogen adsorption–desorption isotherm and the corresponding pore-size distribution curve for hierarchical porous NiO. According to the International Union of Pure and Applied Chemistry (IUPAC) classification, the isotherm curve can be classified as type IV. The hierarchical porous NiO exhibits a specific BET surface of 70.02 m2 g 1. Barrett–Joyner–Halenda (BJH) pore size distribution curve (Fig. 2a, inset) shows a single peak at 10 nm, indicating the uniform mesoporous behavior. These results combined with the FESEM analysis further confirm the hierarchical porous nature of as-prepared sample, which can enhance the ionic diffusion and the charge transfer on the surface of active material [8,19]. The growth mechanism of the hierarchical porous NiO is schematically illustrated in Fig. 2b. First, nickel alkoxide (EG–Ni2 þ (complex)) was obtained and reacted with the hydrated H2O molecules of nickel acetate via a hydrolysis reaction. And then, the hydrolyzed molecules can link together through a condensation reaction to from EG–Ni–O–Ni–EG complex [21,22]. Here, PVP not only is a structure-directing agent to promote the formation of spherical structure, but also can adjust the system viscoelasticity [23]. With the Artemia cyst shells added as the hard template, the obtained product can be slowly immersed into the pores and arranged the wall of pore structure of the shells. Both
500nm 200nm 300nm
500nm
1μm
1μm 200nm
500nm
Pore
Fig. 1. FESEM images of original Artemia cyst shells (a), and Artemia cyst shells after ball milling (b). FESEM images of hierarchical porous NiO (c) and at high magnification (inset). TEM of hierarchical porous NiO (d) and at high magnification (inset). XRD pattern of hierarchical porous NiO (e).
J. He et al. / Materials Letters 128 (2014) 117–120
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Fig. 2. Nitrogen adsorption–desorption isotherms plots and corresponding pore size distribution curve of hierarchical porous NiO (inset) (a). Schematic illustration of the growth mechanism of hierarchical porous NiO (b).
Fig. 3. CV curves of hierarchical porous NiO at different scanning rates (a); discharge curves of hierarchical porous NiO at different current densities (b); specific capacitance variation at different current densities (c); cycling performance of hierarchical porous NiO at 10 A g 1(d) and EIS of hierarchical porous NiO (inset).
PVP and Artemia cyst shells can be removed through calcination in air at 500 1C. Cyclic voltammetry (CV) measurements were evaluated in potential window of 0–0.6 V (vs Hg/HgO), at the scan rates of 5–100 mV s 1 (Fig. 3a). Two strong peaks around 0.3–0.4 V and 0.45–0.55 V are observed from the CV curves, indicating that the superficial faradic reduction and oxidation reactions have taken place respectively. Moreover, the redox couple is owed to the
conversion between NiO and NiOOH, expressed as NiO þ OH
charge
⇄
discharge
NiOOH þ e
ð1Þ
The galvanostatic charge/discharge curves of the as-prepared sample from 0.3 A g 1 to 10 A g 1 can be shown in Fig. 3b. The SC value achieves 493 F g 1 at a low current destiny of 0.3 A g 1, and still retains 459 F g 1 at the current destiny of 10 A g 1, indicating
120
J. He et al. / Materials Letters 128 (2014) 117–120
the high rate performance ( 93%) of the as-prepared product (Fig. 3c). Fig. 3d shows the cycle performance of the sample. The SC remains 443 F g 1 after 2000 cycles at high current density of 10 A g 1, which is about 96% capacitance retention. The EIS of the as-prepared sample were tested under the ac modulation 5 mV in the frequency range from 10 2 to 10 5 Hz (Fig. 3d (inset)). The electrode exhibits low contact resistance and vertical curve at low frequency. This result is comparable to the work from the literature [7,12,15], and presents superior rate performance, which could be mainly attributed to the special interconnected hierarchical porous structure, which creates an effective diffusion channels for OH ions in the electrode/electrolyte, ensuring fast Faradic reactions at high current densities [7,11,14,15]. 4. Conclusions In summary, we introduced a facile and novel biotemplate assisted method to fabricate the hierarchical porous NiO. The original structure of Artemia cyst shells has been successfully replicated. The unique porous structure, with the nanoparticles assembled on the pore wall, promotes good electrochemical performance, including high SC values, high rate performance and good cycling stability. Acknowledgment Financial support from the National Natural Science Foundation of China (Grant 51202213), Natural Science Foundation of Hebei
Province (Grant B2012203043), China Postdoctoral Science Foundation (Grant 2013M530889), Excellent Young Scientist Funding of Hebei Province (Grant Y2012005) and Postdoctoral Foundation in Hebei Province is acknowledged.
References [1] Cheng K, Yang F, Ye K, Yang SN, Yin JL, Wang GL, et al. J Mater Chem A 2013;1:14246–52. [2] Meher SK, Justin P, Rao GR. ACS Appl Mater Interfaces 2011;3:2063–73. [3] Wang YG, Xia YY. Electrochim Acta 2006;51:3223–7. [4] Zhi MJ, Xiang CC, Li JT, Li M, Wu NQ. Nanoscale 2013;5:72–88. [5] Jiang H, Sun T, Li CZ, Ma J. RSC Adv 2011;1:954–7. [6] Meher SK, Justin P, Rao GR. Nanoscale 2011;3:683–92. [7] Xiong SL, Yuan CZ, Zhang XG, Qian YT. CrystEngComm 2011;13:626–32. [8] Liang ZH, Zhu YJ, Hu XL. J Phys Chem B 2004;108:3488–91. [9] Song XF, Gao L, Mathur S. J Phys Chem C 2011;115:21730–5. [10] Song XF, Gao L. J Phys Chem C 2008;112:15299–305. [11] Liu MM, Chang J, Sun J, Gao L. Electrochim Acta 2013;107:9–15. [12] Zhang YQ, Xia XH, Tu JP, Shi YJ, Wang XL, Gu CD. J Power Sources 2012;199:413–7. [13] Xia XH, Tu JP, Wang XL, Gu CD, Zhao XB. J Mater Chem 2011;21:671–9. [14] Yan XY, Tong XL, Wang J, Gong CW, Zhang MG, Liang LP. Mater Lett 2013;95:1–4. [15] Yuan CZ, Zhang XG, Su LH, Gao B, Shen LF. J Mater Chem 2009;19:5772–7. [16] Yang BD, Qi LM, Ma JM. Adv Mater 2002;14:1543–6. [17] Liu ZT, Fan TX, Zhang D. J Am Ceram Soc 2006;89:662–5. [18] Xia Y, Zhang WK, Xiao Z, Huang H, Zeng HJ, Chen XR, et al. J Mater Chem 2012;22:9209–15. [19] Shim HW, Lim AH, Kim JC, Jong JC, Seo SD, et al. Sci Rep 2013;3:1–9. [20] Zhao YF, He J, Fan LD, Ran W, Zhang CM, Gao DW, et al. Int J Hydrog Energy 2013;38:16558–62. [21] Sawangphruk M, Limtrakul J. Mater Lett 2012;68:230–3. [22] Lin LY, Liu TM, Miao B, Zeng W. Mater Lett 2013;102–103:43–6. [23] Ren B, Fan MQ, Wang J, Song DL, Bai XF. Electrochim Acta 2013;92:197–204.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Biotemplate assisted synthesis of 3D hierarchical porous NiO for supercapatior application with excellent rate performance Jing He a, Yufeng Zhao a,n, Ding-Bang Xiong b, Wei Ran a, Jiang Xu a, Yuqin Ren c, Long Zhang a, Yongfu Tang a, Faming Gao a a
Key Laboratory of Applied Chemistry, Yanshan University, Qinhuangdao 066004, China State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, Shanghai 200240, China c Beidaihe Center Experiment Station, Chinese Academy of Fishery Science, 066100 Beidaihe, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 23 January 2014 Accepted 22 April 2014 Available online 2 May 2014
A novel 3D hierarchical porous nickel oxide (NiO) was fabricated by a facile biotemplate assisted method. Physicochemical characterizations indicate that the as prepared hierarchical porous NiO is assembled by multiple-layered porous nanosheets, of which the pore structure is highly ordered. The electrochemical performance of the as prepared hierarchical porous NiO was carried out in 6 M KOH, exhibited relatively high specific capacitance value of 493 F g 1 at a current density of 0.3 A g 1, good rate performance ( 93% capacity retention from 0.3 A g 1 to 10 A g 1), as well as good cycling stability ( 96% retention upon 2000 charge/discharge cycles at 10 A g 1). & 2014 Elsevier B.V. All rights reserved.
Keywords: Hierarchical porous Nickel oxide Supercapacitor AFM Ceramics
1. Introduction Nickel oxide (NiO) is a promising electrode material for supercapacitors, owing to its high theoretical capacity ( 2584 F g 1 within 0.5 V), low cost, easy availability and relatively environmental friendliness [1–3]. However, the poor stability and rate performance, as well as much lower specific capacitance (SC) of NiO electrode than theoretical value, have seriously restricted their extensive applications [4,5]. It is widely reported that the electrochemical performance of NiO is notably related to its morphology and microstructure [6,7]. So far, nickel oxides with various nanostructures, such as nanosheets [8], nanotubes [9], nanospheres [10] and some nanoporous structures [11–15], have been successfully fabricated and used for the electrode materials of supercapacitors. In particular, NiO with three dimensional (3D) hierarchical porous nanostructures, which can normally provide high surface area, continuous electron pathway and fast ion transportation, has shown its unique advantages in improving the cycling stability, rate performance, as well as providing high SC value when used as an electrode for supercapacitors. Nevertheless, most researchers mainly focus on two-dimensional (2D) structured hierarchical porous film [12,13] or hierarchically porous spheres [14,15]. There is few research about the preparation and
n
Corresponding author. Tel.: þ 86 335 8387743. E-mail addresses: [email protected], [email protected] (Y. Zhao), [email protected] (Y. Tang). http://dx.doi.org/10.1016/j.matlet.2014.04.152 0167-577X/& 2014 Elsevier B.V. All rights reserved.
application of NiO with three-dimensional (3D) hierarchical porous structure for supercapacitors. Recently, great efforts have been devoted to synthesis hierarchical porous structure with a template-assisted method, remarkably, biotemplates (such as egg-shell [16], pinwood [17], pollen [18], bacteria [19], etc.) with precise sizes, uniform geometries and stable structure, have been used as producing materials with controllable complex morphologies and multiple porous structures. Previously, we have successfully synthesized hierarchical porous LiNiCuZn-oxides using Artemia cyst shells (AS) as hard template [20]. In this work, a novel 3D hierarchical porous NiO was synthesized by a facile biotemplate assisted method with AS as the hard template and poly(vinylpyrrolidone) (PVP) as the structure-directing agent. The as-prepared NiO successfully replicates the structure of natural Artemia cyst shell, and shows good capacitive performance.
2. Experimental The hierarchical porous NiO was synthesized through a biotemplate assisted method. To elaborate, 0.3 g of PVP and 0.6 g of nickel acetate tetrahydrate (Ni(CH3COOH)2 4H2O) were dissolved in 30 ml ethylene glycol (EG). 0.6 g of ball-milled shells, as the hard template, was added to the obtained solution. The mixture was stirred for 2 h and then kept in the vacuum oven for 6 h at room temperature. Then the as-prepared product was heated at
118
J. He et al. / Materials Letters 128 (2014) 117–120
80 1C for 12 h. Finally, hierarchical porous NiO was obtained after calcination in air at 500 1C for 6 h. The morphology of NiO samples was characterized by FESEM (Hitachi-S4800, 15 kV) and TEM (Hitachi-7650, 80 kV). Powder X-ray diffraction (XRD) patterns of NiO samples were recorded using an X-ray diffractometer (Rigaku, λ ¼1.5418 Å). The specific Brunauer–Emmett–Teller (BET) surface area and pore size distribution were measured using a Micromeritics ASAP2020 analyzer. The electrochemical measurements were carried out through a three-electrode electrochemical system in 6 M KOH electrolyte. Platinum foil, Hg/HgO (0.1 M KOH) and NiO active material coated nickel foam were used as the counterelectrode, reference electrode and working electrode, respectively. The working electrode was fabricated as follows. 80 wt% of as-prepared NiO sample, 15 wt% of acetylene carbon black and 5 wt% PTFE (polytetrafluoroethylene) were mixed to obtain homogeneous slurry. The obtained slurry was coated on a 1 1 cm2 area foam nickel substrate and dried in vacuum at 120 1C for 12 h. The active material loading of the electrode was 4.0 mg cm 2. Cyclic voltammetry (CV) and the electrochemical impedance spectra (EIS) were tested on a CHI660c electrochemical workstation (Chenhua, China). Galvanostatical charge–discharge test was conducted on a LAND battery program-control test system (Land, CT2001A, China).
3. Results and discussion The morphology and microstructure of Artemia cyst shells and the as prepared NiO are shown in Fig. 1. The original Artemia cyst shell is in spherical shape (Fig. 1a). After being ball milled into small pieces, the hierarchical porous structure of Artemia cyst shell is fully exposed (Fig. 1b). The Artemia cyst shell is mainly composed of macropores with diameters from 200 nm to 1 μm. FESEM image of the as-prepared NiO (Fig. 1c) shows that the 3D
hierarchical porous NiO is assembled by highly ordered macropores from 200 to 500 nm of which the structure is multi-layered and perfectly interconnected. And the pore wall is assembled by NiO nanoparticles from 20 to 75 nm (inset of Fig. 1d). The TEM image (Fig. 1d) confirms the hierarchical porous architecture of the as-prepared NiO, which indicates that the as-prepared hierarchical porous NiO has successfully replicated the original structure of Artemia cyst shells. The XRD patterns of the as-prepared product (Fig. 1e) indicate characteristic peaks of cubic NiO (space group Fm3m (225)), according to the standard card of JCPDS no. 47-1049. No impurities are observed. Fig. 2a shows the nitrogen adsorption–desorption isotherm and the corresponding pore-size distribution curve for hierarchical porous NiO. According to the International Union of Pure and Applied Chemistry (IUPAC) classification, the isotherm curve can be classified as type IV. The hierarchical porous NiO exhibits a specific BET surface of 70.02 m2 g 1. Barrett–Joyner–Halenda (BJH) pore size distribution curve (Fig. 2a, inset) shows a single peak at 10 nm, indicating the uniform mesoporous behavior. These results combined with the FESEM analysis further confirm the hierarchical porous nature of as-prepared sample, which can enhance the ionic diffusion and the charge transfer on the surface of active material [8,19]. The growth mechanism of the hierarchical porous NiO is schematically illustrated in Fig. 2b. First, nickel alkoxide (EG–Ni2 þ (complex)) was obtained and reacted with the hydrated H2O molecules of nickel acetate via a hydrolysis reaction. And then, the hydrolyzed molecules can link together through a condensation reaction to from EG–Ni–O–Ni–EG complex [21,22]. Here, PVP not only is a structure-directing agent to promote the formation of spherical structure, but also can adjust the system viscoelasticity [23]. With the Artemia cyst shells added as the hard template, the obtained product can be slowly immersed into the pores and arranged the wall of pore structure of the shells. Both
500nm 200nm 300nm
500nm
1μm
1μm 200nm
500nm
Pore
Fig. 1. FESEM images of original Artemia cyst shells (a), and Artemia cyst shells after ball milling (b). FESEM images of hierarchical porous NiO (c) and at high magnification (inset). TEM of hierarchical porous NiO (d) and at high magnification (inset). XRD pattern of hierarchical porous NiO (e).
J. He et al. / Materials Letters 128 (2014) 117–120
119
Fig. 2. Nitrogen adsorption–desorption isotherms plots and corresponding pore size distribution curve of hierarchical porous NiO (inset) (a). Schematic illustration of the growth mechanism of hierarchical porous NiO (b).
Fig. 3. CV curves of hierarchical porous NiO at different scanning rates (a); discharge curves of hierarchical porous NiO at different current densities (b); specific capacitance variation at different current densities (c); cycling performance of hierarchical porous NiO at 10 A g 1(d) and EIS of hierarchical porous NiO (inset).
PVP and Artemia cyst shells can be removed through calcination in air at 500 1C. Cyclic voltammetry (CV) measurements were evaluated in potential window of 0–0.6 V (vs Hg/HgO), at the scan rates of 5–100 mV s 1 (Fig. 3a). Two strong peaks around 0.3–0.4 V and 0.45–0.55 V are observed from the CV curves, indicating that the superficial faradic reduction and oxidation reactions have taken place respectively. Moreover, the redox couple is owed to the
conversion between NiO and NiOOH, expressed as NiO þ OH
charge
⇄
discharge
NiOOH þ e
ð1Þ
The galvanostatic charge/discharge curves of the as-prepared sample from 0.3 A g 1 to 10 A g 1 can be shown in Fig. 3b. The SC value achieves 493 F g 1 at a low current destiny of 0.3 A g 1, and still retains 459 F g 1 at the current destiny of 10 A g 1, indicating
120
J. He et al. / Materials Letters 128 (2014) 117–120
the high rate performance ( 93%) of the as-prepared product (Fig. 3c). Fig. 3d shows the cycle performance of the sample. The SC remains 443 F g 1 after 2000 cycles at high current density of 10 A g 1, which is about 96% capacitance retention. The EIS of the as-prepared sample were tested under the ac modulation 5 mV in the frequency range from 10 2 to 10 5 Hz (Fig. 3d (inset)). The electrode exhibits low contact resistance and vertical curve at low frequency. This result is comparable to the work from the literature [7,12,15], and presents superior rate performance, which could be mainly attributed to the special interconnected hierarchical porous structure, which creates an effective diffusion channels for OH ions in the electrode/electrolyte, ensuring fast Faradic reactions at high current densities [7,11,14,15]. 4. Conclusions In summary, we introduced a facile and novel biotemplate assisted method to fabricate the hierarchical porous NiO. The original structure of Artemia cyst shells has been successfully replicated. The unique porous structure, with the nanoparticles assembled on the pore wall, promotes good electrochemical performance, including high SC values, high rate performance and good cycling stability. Acknowledgment Financial support from the National Natural Science Foundation of China (Grant 51202213), Natural Science Foundation of Hebei
Province (Grant B2012203043), China Postdoctoral Science Foundation (Grant 2013M530889), Excellent Young Scientist Funding of Hebei Province (Grant Y2012005) and Postdoctoral Foundation in Hebei Province is acknowledged.
References [1] Cheng K, Yang F, Ye K, Yang SN, Yin JL, Wang GL, et al. J Mater Chem A 2013;1:14246–52. [2] Meher SK, Justin P, Rao GR. ACS Appl Mater Interfaces 2011;3:2063–73. [3] Wang YG, Xia YY. Electrochim Acta 2006;51:3223–7. [4] Zhi MJ, Xiang CC, Li JT, Li M, Wu NQ. Nanoscale 2013;5:72–88. [5] Jiang H, Sun T, Li CZ, Ma J. RSC Adv 2011;1:954–7. [6] Meher SK, Justin P, Rao GR. Nanoscale 2011;3:683–92. [7] Xiong SL, Yuan CZ, Zhang XG, Qian YT. CrystEngComm 2011;13:626–32. [8] Liang ZH, Zhu YJ, Hu XL. J Phys Chem B 2004;108:3488–91. [9] Song XF, Gao L, Mathur S. J Phys Chem C 2011;115:21730–5. [10] Song XF, Gao L. J Phys Chem C 2008;112:15299–305. [11] Liu MM, Chang J, Sun J, Gao L. Electrochim Acta 2013;107:9–15. [12] Zhang YQ, Xia XH, Tu JP, Shi YJ, Wang XL, Gu CD. J Power Sources 2012;199:413–7. [13] Xia XH, Tu JP, Wang XL, Gu CD, Zhao XB. J Mater Chem 2011;21:671–9. [14] Yan XY, Tong XL, Wang J, Gong CW, Zhang MG, Liang LP. Mater Lett 2013;95:1–4. [15] Yuan CZ, Zhang XG, Su LH, Gao B, Shen LF. J Mater Chem 2009;19:5772–7. [16] Yang BD, Qi LM, Ma JM. Adv Mater 2002;14:1543–6. [17] Liu ZT, Fan TX, Zhang D. J Am Ceram Soc 2006;89:662–5. [18] Xia Y, Zhang WK, Xiao Z, Huang H, Zeng HJ, Chen XR, et al. J Mater Chem 2012;22:9209–15. [19] Shim HW, Lim AH, Kim JC, Jong JC, Seo SD, et al. Sci Rep 2013;3:1–9. [20] Zhao YF, He J, Fan LD, Ran W, Zhang CM, Gao DW, et al. Int J Hydrog Energy 2013;38:16558–62. [21] Sawangphruk M, Limtrakul J. Mater Lett 2012;68:230–3. [22] Lin LY, Liu TM, Miao B, Zeng W. Mater Lett 2013;102–103:43–6. [23] Ren B, Fan MQ, Wang J, Song DL, Bai XF. Electrochim Acta 2013;92:197–204.