Anions on Morphologies of the Nanosized Nickel Hydroxide

Jun 24, 2010 - Changchun 130022, People's Republic of China, and The Amour Technology Institute of PLA,. Changchun 130117, People's Republic of ...
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Influence of OH- and SO42- Anions on Morphologies of the Nanosized Nickel Hydroxide Dehui Sun,*,† Jilin Zhang,*,‡ Huijuan Ren,† Zhenfeng Cui,† and Dexin Sun§ Changchun Institute of Technology, Changchun 130012, People’s Republic of China, State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China, and The Amour Technology Institute of PLA, Changchun 130117, People’s Republic of China ReceiVed: April 15, 2010; ReVised Manuscript ReceiVed: June 10, 2010

The nickel hydroxides (β-Ni(OH)2) with different shapes such as hexagonal nanosheets, irregular nanosheets, and nanoparticles were synthesized in the absence of SO42- ions and in the presence of 0.00-3.00 mmol of the added NaOH using a hydrothermal method. The β-Ni(OH)2 phase with brucite-type structure was confirmed by an energy-dispersive spectrum (EDS), Fourier transform infrared spectra (FTIR), and powder X-ray diffraction (XRD). The effect of the free OH- ions and the SO42- ions in the hydrothermal system on morphologies of the Ni(OH)2 products was investigated in detail. In the absence of SO42- ions system, when the added NaOH amount is less than 0.02 mmol, the irregular thin nickel hydroxide nanosheets with thickness of about 20-50 nm were obtained; when the added NaOH amount is between 0.35 and 0.55 mmol, the products have the regular hexagonal morphology with a width of 150-500 nm and thickness of 40-80 nm; while when the added NaOH amount is 1.50-3.00 mmol, the nickel hydroxide products became polyhedral nanoparticles with an average diameter of ca. 50-90 nm. The Ni(SO4)0.3(OH)1.4 nanowires or R-Ni(OH)2 nanowires containing the intercalated SO42- anions can only be obtained in the presence of SO42- ions. They have lengths of several micrometers and widths of 20-30 nm. A possible growth mechanism of the nanosheets, nanoparticles, and nanowires is suggested. 1. Introduction Ni(OH)2 has become a well-known positive electrode active material in the nickel-based rechargeable alkaline batteries (e.g., Ni/Cd, Ni/H2, Ni/MH, Ni/Fe, and Ni/Zn) due to its high proton diffusion coefficient, high power density, high energy, and so on. But its morphology has significant influence on the electrochemical performance.1-5 For example, compared with commercial Ni(OH)2, R-Ni(OH)2 with three-dimensional (3D) flowerlike nanostructures exhibited superior cycling reversibility and improved capacity.6 The nanoboards exhibited the highest specific capacity with being close to the theoretical capacity of β-Ni(OH)2.7 A mixture of β-Ni(OH)2 nanofibers and nanoparticles was expected to yield at least a 20% improvement in cathode energy content.8 Thus, considerable efforts have been recently devoted to synthesize different morphologies of nickel hydroxide such as nanofibres, nanotubes, nanorods, nanoribbons, nanoboards, and nanoflowers.6-13 On one hand, it is expected that the Ni(OH)2 nanostructure with various morphologies could have potential applications in high-energy-density batteries. On the other hand, it is expected that they could contribute to a better understanding of their formation mechanism so as to be able to control synthesis and to exhibit interesting electrochemical performance. Shapes of the Ni(OH)2 nanocrystals depend mainly on the intrinsic structure of the crystal and are affected by the external reaction conditions such as reaction temperature and pressure, adsorbent or coordination ions, and concentration of the reactants.14-16 Ocan˜a17 reported that preparation of the needlelike * To whom correspondence should be addressed. E-mail: dhsun998@ gmail.com (D.S.); [email protected] (J.Z.). † Changchun Institute of Technology. ‡ Chinese Academy of Sciences. § The Amour Technology Institute of PLA.

particles of nickel basic sulfate (Ni(OH)1.4(SO4)0.3) used a forced hydrolysis method in an aqueous solutions containing the appropriated concentration of the nickel(II) nitrate, nickel(II) sulfate, and sodium acetate. He found that the sulfate or acetate concentrations affected the morphological characteristics of the particles. The effects were attributed to the ability of such anions to form soluble metal complexes, which act as precursors to the solid phase formation. Liu’s group18 prepared Ni(OH)2 nanoribbons containing the intercalated SO42- anions (namely Ni(OH)1.66(SO4)0.17(H2O)0.29) by hydrothermal treatment of amorphous R-Ni(OH)2 powder in the presence of high concentrations of nickel sulfate. They confirmed that high concentrations of nickel sulfate were necessary in the treatment process for the synthesis of the nanoribbons. Zhang et al.19 prepared Ni(SO4)0.3(OH)1.4 nanobelts by a hydrothermal reaction using ammonia as precipitator and confirmed that the nanobelt is a single crystal grown parallel to (010) and enclosed by (100) and (001) as the top and side planes, respectively. Liang et al.20 obtained β-Ni(OH)2 nanosheets by a hydrothermal method at 200 °C using nickel acetate as the nickel source and aqueous ammonia as both an alkaline and complexing reagent. They investigated the influence of pH ) 7.5 and pH ) 9.6 on the product and found that there was no change of the morphology except the limited influence on the sizes of nanosheets under the same other experimental conditions. They have confirmed that the surface of the nanosheets is the {0001} planes of the hexagonal β-Ni(OH)2 phase. Dong et al.21 prepared R-Ni(OH)2 nanobelts, nanowires, short nanowires, and β-Ni(OH)2 nanoplates by a hydrothermal method containing NaOH, NiSO4, and water. They found that the molar ratio of NaOH to NiSO4 (R ) [Ni2+]/[OH-]) strongly affects the morphology and crystal phase of the Ni(OH)2. At R g 1, R-Ni(OH)2 nanobelts or nanowires and short nanowires containing the intercalated SO42-

10.1021/jp1033849  2010 American Chemical Society Published on Web 06/24/2010

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Figure 1. FE-SEM images (a, b, c, and e) and EDS spectra (d and f) of the β-Ni(OH)2 nanosheets prepared in the absence of SO42- ions and in the range of the 0.00-0.55 mmol NaOH amount: (a) 0.00 mmol; (b) 0.02 mmol; (c, d) 0.35 mmol; (e, f) 0.50 mmol.

anions (Ni(SO4)0.3(OH)1.4), JCPDF No. 41-1424) were always obtained after hydrothermal treatment regardless of the temperature. At R e 1/2, only β-Ni(OH)2 nanoplates were generated. At 1/2 e R e 1, such as R ) 3/4, temperature played a very important role in determining the morphology and crystallographic phase of the final product. However, the influence of anions such as SO42- and OH- on morphologies of the nanosized nickel hydroxide still needs further investigation because the previous works were performed in the presence of other anions such as SO42-, CH3COO-, NO3- together with OH-. In this paper, we found that under present hydrothermal conditions, the hexagonal β-Ni(OH)2 nanoplate, irregular nanosheets, and nanoparticles were always produced in the presence of 0.00-3.00 mmol of the added NaOH solution without containing SO42- ions in the system, while Ni(SO4)0.3(OH)1.4 nanowires or R-Ni(OH)2 nanowires containing intercalated SO42- anions were obtained in the presence of SO42ions. A possible growth mechanism of the nanosheets, nanowires, and nanoparticles is discussed.

2. Experimental Section Preparation of Nickel Hydroxide Samples. Nickel sulfate (NiSO4 · 6H2O), barium chloride (BaCl2), and sodium hydroxide (NaOH) were of analytical grade and were supplied by the Beijing Chemical Factory, People’s Republic of China. All chemicals were directly used without further purification. Deionized water was used throughout. The Ni(OH)2 nanosheets were synthesized in the absence of SO42- ions. In a typical procedure, an amorphous Ni(OH)2 precipitate was first prepared by adding 12.50 mL of NiSO4 (0.60 mol/L) solution to 3.50 mL of NaOH (5.00 mol/L) solution at room temperature under magnetic stirring. The precipitate was immediately filtered under reduced pressure and washed repeatedly with deionized water until the SO42- ions were not detected with one drop of BaCl2 solution (0.10 mol/L). Then the precipitate was transferred into a 40 mL of Teflon-lined stainless steel autoclave; subsequently, 0.00-0.55 mmol of NaOH and deionized water was added into the autoclave under stirring and reached 80% of autoclave volume. The autoclave

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Figure 2. FE-SEM images (a, b, c, and e) and EDS spectra (d and f) of the β-Ni(OH)2 nanoparticles prepared in the absence of SO42- ions and in the range of the 1.50-3.00 mmol NaOH amount: (a) 1.50 mmol; (b) 2.00 mmol; (c, d) 2.50 mmol; (e, f) 3.00 mmol.

was sealed and maintained in an oven at 180 °C for 24 h. After the reaction was completed, the autoclaves were cooled down naturally to room temperature. The resulting green Ni(OH)2 samples were filtered under reduced pressure and washed repeatedly with deionized water to remove any impurities possibly remaining in the final product, and finally dried at 45 °C in an oven in air. The nickel hydroxide nanoparticles can be prepared through controlling the amount of the added NaOH (1.50-3.00 mmol) according to the same method as the above nanosheet synthesis. The nanowire samples were prepared as follows: First, 5.0 g of NiSO4 · 6H2O were dissolved in 25 mL of deionized water to form a green NiSO4 solution. Then, the NiSO4 solution reacts with equivalent mole NaOH solution (5.0 mol/L) at room temperature under magnetic stirring, forming an Ni(OH)2 suspension with the excess NiSO4 solution. Subsequently, the suspension was transferred into a Teflon-lined stainless steel autoclave (40 mL), and deionized water was added into the autoclave until whole volume of the mixture reached 32.0 mL (namely, 80% of autoclave volume). Next, after stirring for 10

Figure 3. XRD patterns of the β-Ni(OH)2 nanosheets, nanoparticles, and amorphous β-Ni(OH)2 precipitate.

min, the autoclave was sealed and maintained in an oven at 180 °C for 24 h and then cooled down naturally to room

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Figure 4. FTIR spectra of the β-Ni(OH)2 nanosheets and nanoparticles.

temperature. The nanowire sample was obtained after filtered, washed repeatedly with deionized water, and dried at 45 °C in an oven in air. Characterization. Field emission scanning electron microscopy (FE-SEM) images and EDS (energy dispersive spectrum) were carried out on a PHILIPS XL30 scanning electron microscope equipped with energy dispersive spectroscopy. Powder X-ray diffraction (XRD) patterns were collected on a Rigaku D/2500 V/PC X-ray diffractometer using Cu KR radiation (λ ) 1.5418 Å) at a scanning speed rate of 15° min-1 and the detective range from 10° to 80°. Fourier transform infrared spectra (FTIR) were recorded with the KBr pellet technique in the range of 4000-400 cm-1 on a model FTS135 infrared spectrophotometer (American BIO-RAD Company) operated at a resolution of 2 cm-1. All the measurements were performed at room temperature (RT). 3. Results and Discussion 3.1. Morphologies of the Ni(OH)2 Nanosheets and Nanoparticles. The morphologies of the Ni(OH)2 nanosheets prepared in the absence of SO42- ions and in the range of 0.00-0.55 mmol of the added NaOH were investigated by FE-SEM. The SEM images in Figure 1 show that the Ni(OH)2 samples have the sheetlike morphologies. According to the experimental results, when the added NaOH amount is less than 0.02 mmol, the irregular thin nickel hydroxide nanosheets with thickness of about 20-50 nm were obtained, and when the added NaOH amount is between 0.35 and 0.55 mmol, the products have the regular hexagonal morphology with a width of 150-500 nm and thickness of 40-80 nm. Interestingly, when the added NaOH amount is 1.50-3.00 mmol, the nickel hydroxide products became nanoparticles, as are shown in Figure 2. These

J. Phys. Chem. C, Vol. 114, No. 28, 2010 12113 nanoparticles take on sphericity-like or polyhedral shape with an average diameter of ca. 50-90 nm. They seem homogeneously sized and well-dispersed. The corresponding EDS spectra in parts d and f of Figures 1 and 2 show that these products consist of nickel and oxygen elements due to exclusion of the Au and Si elements. This is because the Au in the EDS is from the sprayed gold on surface of the sample and Si roots in single silicon wafer used as supporting the samples. 3.2. Structure of the Ni(OH)2 Nanosheets and Nanoparticles. Figure 3 gives X-ray diffraction (XRD) patterns of the nanosheet, the nanoparticle, and the Ni(OH)2 precipitate before hydrothermal crystallization process. All the diffraction peaks can be readily indexed to the hexagonal β-Ni(OH)2 based on the JCPDS file No. 14-0117. The diffraction peaks in the Ni(OH)2 precipitate before hydrothermal treatment are remarkably broadened. This shows that it is amorphous. The diffraction peak positions and intensities in the nanosheet and the nanoparticle are well consistent with those of the hexagonal β-Ni(OH)2 structure (JCPDS 14-0117). This indicates that they are well-crystallized in the β-Ni(OH)2 phase. Their FTIR spectra in the Figure 4 almost have the same vibration absorption bands at ca. 3642, 3424, 1637, 527, and 454 cm-1. The bands at ca. 454 and 527 cm-1 result from an in-plane Ni-O-H bending vibration and Ni-O stretching vibration, respectively. The broad bands at ca. 1637 cm-1 can be assigned to the bending vibrational mode of the absorbed water. The broad band at ca. 3424 cm-1 is due to hydrogen-bonded O-H groups stretching vibration, while the narrow band at ca. 3642 cm-1 is attributed to non-hydrogen-bonded O-H groups stretching vibration.9,10,22,23 This can further confirm that the nanosheet and the nanoparticle have the same β-Ni(OH)2 structure. 3.3. Morphologies of the Ni(OH)2 Nanowires. FE-SEM image and EDS of the nanowire sample are presented in Figure 5. The FE-SEM image in Figure 5a reveals that the sample consists of a large number of nanowires. They have lengths of several micrometers and widths of 20-30 nm. EDS analyzing result of the nanowires in Figure 5b shows that the nanowires are composed of the nickel, oxygen, and sulfur elements. The presence of Au in the EDS is due to the sprayed gold on surface of the sample so as to obtain good electrical conduction. 3.4. Structue of the Ni(OH)2 Nanowires. Figure 6 shows the XRD pattern of the nanowire products. In the XRD pattern the diffraction peak positions and intensities of the nanowires are well agreement with those of the Ni(SO4)0.3(OH)1.4 (JCPDS 41-1424). This indicates that nanowire samples were Ni(SO4)0.3(OH)1.4 rather than β-Ni(OH)2. This is in accordance with the analysis result of the EDS. The conclusion can be further confirmed by FTIR result. The FTIR spectrum of the

Figure 5. FE-SEM image (a) and EDS spectrum (b) of the nanowire samples.

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Figure 9. FTIR of the nanosheet and nanowire sample. Figure 6. XRD of the Ni(SO4)0.3(OH)1.4 nanowires.

Figure 7. FTIR spectra of the Ni(SO4)0.3(OH)1.4 nanowires.

Ni(SO4)0.3(OH)1.4 nanowires is shown in Figure 7. The band at ca. 456 cm-1 can be assigned to Ni-O vibrations. The bands between 590 and 1200 cm-1 originate from SO42- and HSO4vibrations, and the band at ca. 1112 cm-1 is mainly due to HSO4- vibrations. The broad band at ca. 1627 and 3460 cm-1 may result from bending and stretch vibrational modes of the absorbed water or water in air, respectively. The narrow band at ca. 3607 cm-1 is attributed to the O-H bond stretching vibration.6,22-25 This indicates that the nanowire sample is R-Ni(OH)2 phase containing the intercalated SO42- anions. 3.5. Possible Growth Mechanism of the Products. Nickel hydroxide has a hexagonal layered structure with two poly-

Figure 10. XRD of the nanosheet and nanowire sample.

morphs, R- and β-phases.6,7 R-Ni(OH)2 is isostructural with hydrotalcite and consists of stacked Ni(OH)2-x layers intercalated with various anions or water molecules.7 It can be formulated as Ni(OH)2-x(An-)x/n · yH2O, where x ) 0.2-0.4, y ) 0.6-1, and A is chloride, sulfate, nitrate, carbonate, or other anions. β-Ni(OH)2 has a well-ordered brucite-like structure and is composed of an ABAB oxygen stacking sequence along the c axis.6,10,13 It does not contain any intercalated species.7,13 The R-Ni(OH)2 phase is thermodynamically unstable and rapidly transforms to the β-Ni(OH)2 phase upon aging in alkaline solution. For formation of the hexagonal nanosheets, irregular nanosheets, and nanoparticles with β-Ni(OH)2 structure in the

Figure 8. FE-SEM image of the sample prepared in the presence of the trace SO42- ions and 0.03 mmol of the added NaOH. (a) Low magnification. (b) High magnification.

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Figure 11. EDS spectra of the Ni(SO4)0.3(OH)1.4 nanowires (a) and β-Ni(OH)2 nanosheets (b) in the sample prepared in the presence of the trace SO42- ions and 0.03 mmol of the added NaOH amount.

Figure 12. Formation scheme of the Ni(OH)2 with different shapes and the Ni(SO4)0.3(OH)1.4 nanowires: (a) NaOH ) 0.00-0.020 mmol; (b) NaOH ) 0.35-0.55 mmol; (c) NaOH ) 1.50-3.00 mmol; (d) trace SO42- ions; (e) large numbers of SO42- ions.

absence of SO42- ions, we think that amorphous Ni(OH)2 first forms crystal seeds in the hydrothermal process and then gradually grows through “dissolution-crystallization mechanism”. This mainly deals with two sides. First, the intrinsic crystal structure is the key factor for the morphology growth of the platelike β-Ni(OH)2. Since the β-Ni(OH)2 is the layered structure composed of an ABAB oxygen stacking sequence along the c axis, it tends to form into a thin flake or sheet shape in natural/normal formation environments. This is because the Ni2+ ions bordering upon the (100) or (010) plane link with OH- ions, while the Ni2+ ions located at (001) plane were separated by two layers of OH- ions. Compared with the electrostatic repulsion of the (100) or (010) plane, that of the (001) planes is large because of possessing more negative electric charges on its surface. The structural feature is in favor of Ni(OH)2 rapid crystal growth alone 100 and 010 direction to form platelike products and thus to avoid a larger electrostatic repulsion.26 Moreover, the sheets with thickness direction along c-axis can be easily formed because the hexagonal β-Ni(OH)2 sheetlike nanocrystals are thermodynamically stable.7,24 Second, morphology of the β-Ni(OH)2 can be also influenced by the external factors such as OH- concentration. Within range of the free OH- concentration, different electrostatic repulsion of the crystal planes results in anisotropy growth of the β-Ni(OH)2 with different extent and finally lead to the products having different morphologies. Therefore, we infer that an appropriate range of the added NaOH (e.g., 0.35-0.55 mmol) under present experimental conditions could just meet hexagonal β-Ni(OH)2 anisotropy crystal growth demands and result in the formation of the regular hexagonal β-Ni(OH)2 nanosheets. When the

synthetic system has a smaller free OH- concentration, in order to decrease the electrostatic repulsion of the crystal growth along (001) plane, the β-Ni(OH)2 nanosheets tends to rapid crystal growth along (100) and (010) direction and thus the irregular thin hexagonal shapes were formed. When the free OHconcentration is high enough, the electrostatic repulsion between the different crystal planes could tend to same or have small difference and thus the product almost became isotropic crystal growth, finally forming the β-Ni(OH)2 nanoparticles. For formation of the Ni(SO4)0.3(OH)1.4 nanowires in the presence of SO42- ions, we suggest that the SO42- ions can play a capping agent role in crystal growth and result in anisotropic crystal growths in the dissolution-crystallization process. The SO42- steric hindrance effect remarkably influenced the growth speed of the different crystal plane, leading to formation of the Ni(SO4)0.3(OH)1.4 nanowires. The reasons are as follows: First, it has been demonstrated that various anions such as CO32-, SO42-, OH-, F-, Cl-, Br-, and NO3- are able to enter the interlayers of the β-Ni(OH)2 and the relative affinity of the layers toward these anions follows the order: CO32- > SO42- > OH> F- > Cl- > Br- > NO3-.27,28 Second, Liu’s group18 research results have confirmed that high concentrations of nickel sulfate were necessary in the hydrothermal treatment process for the synthesis of the Ni(OH)1.66(SO4)0.17(H2O)0.29 nanoribbons. Third, Dong and co-workers’ research results have shown that the Ni(SO4)0.3(OH)1.4 nanowires took place anisotropic growth after different hydrothermal treatment times between 0 and 96 h at 160 °C, with the value of R ) 3.20 Fourthly, we guess that if the Ni(OH)2 precipitate before hydrothermal crystallization contains trace SO42- ions, the nanosheets and nanowires sample

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should be obtained in the experiments because steric hindrance effect of the trace SO42- ions can merely produce partial nanowires. As was expected, the mixture of the β-Ni(OH)2 nanosheets which are close to rounded or hexagonal-like shape and Ni(SO4)0.3(OH)1.4 nanowires with lengths of scores of micrometers and widths of 20-50 nm was synchronously produced, as shown in Figure 8. The FTIR spectrum in Figure 9 shows that the FTIR characteristic peaks of the Ni(SO4)0.3(OH)1.4 and the β-Ni(OH)2 can be observed. The band at ca. 456 cm-1 can be assigned to Ni-O vibrations. The bands between 590 and 1200 cm-1 originate from SO42- and HSO4vibrations, and the band at ca. 1112 cm-1 is mainly due to HSO4- vibrations. The broad band at ca. 1627 and 3460 cm-1 may result from bending and stretch vibrational modes of the absorbed water or water in air, respectively. The narrow band at ca. 3607 cm-1 is attributed to the O-H bond stretching vibration.6,22-25 The XRD pattern in Figure 10 further confirms that the product is a mixture of β-Ni(OH)2 and Ni(SO4)0.3(OH)1.4. The diffraction peak positions and intensities marked with an asterisk are well in agreement with those of the Ni(SO4)0.3(OH)1.4 phase (JCPDS 41-1424), while the diffraction peak positions and intensities marked a plus sign are almost the same as those of β-Ni(OH)2 phase (JCPDS 14-0117). This indicates that the sample is composed of the Ni(SO4)0.3(OH)1.4 phase and β-Ni(OH)2 phase. It can be inferred that the Ni(SO4)0.3(OH)1.4 phase is made of nanowires, while β-Ni(OH)2 phase is composed of nanosheets. To verify the speculation, the EDS spectra have been examined through respectively choosing nanowires and nanosheets in the sample as detection object. Figure 11 gives EDS spectra of the Ni(SO4)0.3(OH)1.4 nanowires and β-Ni(OH)2 nanosheets in the sample prepared in the presence of the trace SO42- ions and 0.03 mmol of the added NaOH amount. The EDS spectrum of the nanowires in Figure 11a can prove that the nanowires belong to Ni(SO4)0.3(OH)1.4 phase because the EDS spectrum of the nanowires is composed of Ni, O, and S elements. While the EDS spectrum of the nanosheets in Figure 11b can affirm that the nanosheets is β-Ni(OH)2 phase because the EDS spectrum of the nanosheets consists of Ni and O elements but do not include S. Of course, Au and Si elements in the EDS spectra can be excluded from the sample due to the same as the foregoing reason. According to the above analysis and our experimental results, a possible growth mechanism of the nanosheets, nanoparticles, and nanowires is schematically illustrated in Figure 12. 4. Conclusions The nickel hydroxides with different shapes such as hexagonal nanosheets, irregular nanosheets, and nanoparticles with the β-Ni(OH)2 structure as well as nanowires (Ni(SO4)0.3(OH)1.4) were synthesized using a hydrothermal method through controlling the SO42- ions and the OH- ions in the system. In the absence of SO42- ions, when the added NaOH amount is less than 0.02 mmol, the irregular thin nickel hydroxide nanosheets with thickness of about 20-50 nm were obtained; when the added NaOH amount is between 0.35 and 0.55 mmol, the

Sun et al. products have the regular hexagonal morphology with a width of 150-500 nm and thickness of 40-80 nm; when the added NaOH amount is 1.50-3.00 mmol, the nickel hydroxide products became nanoparticles. The EDS, FTIR, and XRD confirmed that the prepared Ni(OH)2 samples have the typical β-phase with brucite-type structure except the nanowires belong to Ni(SO4)0.3(OH)1.4 phase. A possible growth mechanism of the nanosheets, nanoparticles, and nanowires is proposed. Acknowledgment. The work was financially supported by the National Science Foundation of China (Nos. 50473002 and 20871083), the Department of Education of Jilin Province of China (Nos. 2008-371 and 2008-210), the Innovative Plan Foundation of Changchun Institute of Application Chemistry, CAS, China (No. CX07QZJC-29), and Changchun Institute of Technology (No. 32008045). References and Notes (1) Chen, J.; Cheng, F. Y. Acc. Chem. Res. 2009, 42, 713–723. (2) Taniguchi, A.; Fujioka, N.; Ikoma, M.; Ohta, A. J. Power Sources 2001, 100, 117–124. (3) Shukla, A. K.; Venugopalan, S.; Hariprakash, B. J. Power Sources 2001, 100, 125–148. (4) Morioka, Y.; Narukawa, S.; Itou, T. J. Power Sources 2001, 100, 107–116. (5) Watanabe, K.; Kikuoka, T. J. Appl. Electrochem. 1995, 25, 219– 226. (6) Liu, B. H.; Yu, S. H.; Chen, S. F.; Wu, C. Y. J. Phys. Chem. B 2006, 110, 4039–4046. (7) Yang, D.; Wang, R.; He, M.; Zhang, J.; Liu, Z. J. Phys. Chem. B 2005, 109, 7654–7658. (8) Reisner, D. E.; Salkind, A. J.; Strutt, P. R.; Xiao, T. D. J. Power Sources 1997, 65, 231–233. (9) Guan, X. Y.; Deng, J. C. Mater. Lett. 2007, 61, 621–625. (10) Yang, L. X.; Zhu, Y. J.; Tong, H.; Liang, Z. H.; Li, L.; Zhang, L. J. Solid State Chem. 2007, 180, 2095–2101. (11) Cao, M.; He, X.; Chen, J.; Hu, C. Cryst. Growth Des. 2007, 7, 170–174. (12) Zhang, S.; Zeng, H. Chem. Mater. 2009, 21, 871–883. (13) Xu, L.; Ding, Y. S.; Chen, C. H.; Zhao, L.; Rimkus, C.; Joesten, R.; Suib, S. L. Chem. Mater. 2008, 20, 308–316. (14) Lee, S. M.; Cho, S. N.; Cheon, J. AdV. Mater. 2003, 15, 441–444. (15) Wu, J.; Zhang, H.; Du, N.; Ma, X.; Yang, D. J. Phys. Chem. B 2006, 110, 11196–11198. (16) Yan, J.; Chen, W.; Dai, Y.; Meng, D.; Wu, H. Chin. Mater. ReV. 2006, 20, 138–148. (17) Ocan˜a, M. J. Colloid Interface Sci. 2000, 228, 259–262. (18) Yang, D.; Wang, R.; Zhang, J.; Liu, Z. J. Phys. Chem. B 2004, 108, 7531–7533. (19) Zhang, K.; Wang, J.; Lu, X.; Li, L.; Tang, Y.; Jia, Z. J. Phys. Chem. C 2009, 113, 142–147. (20) Liang, Z. H.; Zhu, Y. J.; Hu, X. L. J. Phys. Chem. B 2004, 108, 3488–3491. (21) Dong, L.; Chu, Y.; Sun, W. Chem.-Eur. J. 2008, 14, 5064–5072. (22) Ramesh, T. N.; Vishnu Kamath, P. J. Power Sources 2006, 156, 655–661. (23) Rajamathi, M.; Kamath, P. V.; Seshadri, R. J. Mater. Chem. 2000, 10, 503–506. (24) Chen, D.; Gao, L. Chem. Phys. Lett. 2005, 405, 159–164. (25) Sun, J.; Cheng, J.; Wang, C.; Ma, X.; Li, M.; Yuan, L. Ind. Eng. Chem. Res. 2006, 45, 2146–2149. (26) Wang, W. D.; Liu, J. H.; Wang, D. Z.; Chen, C. H. Chin. J. Process. Eng. 2006, 6, 128–131. (27) Li, H.; Ma, J. Chem. Mater. 2006, 18, 4405–4414. (28) Newman, S. P.; Jones, W. New J. Chem. 1998, 2, 105–115.

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