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silica nanocomposite catalysts for hydrogen generation from hydrolysis of NaBH4 solution
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Materials Letters 62 (2008) 1451 – 1454 www.elsevier.com/locate/matlet
Ni/Ag/silica nanocomposite catalysts for hydrogen generation from hydrolysis of NaBH4 solution Yingbo Chen, Hern Kim ⁎ Department of Environmental Engineering and Biotechnology, Myongji University, San 38-2 Namdong, Yongin, Kyonggi-do 449-728, Republic of Korea Received 4 June 2007; accepted 28 August 2007 Available online 6 September 2007
Abstract Ni/Ag/silica nanocomposite catalysts were prepared by three procedures—nickel coated to amine functionalized silica directly, nickel coated on the surface of Ag/silica nanocomposites reduced by formaldehyde and NaBH4, respectively. The properties and morphologies of the Ni/Ag/silica nanocomposite catalysts were studied by UV–Visible spectra and scanning electron microscopy. The novel catalysts were applied for hydrogen generation from hydrolysis of NaBH4. A rate of hydrogen generation per unit nickel as high as 2600 ml/min/g Ni was obtained with 150 mM NaBH4 at 30 °C, which notes that these nanocomposites can be used as a competitive catalytic material for hydrogen generation via hydrolysis of NaBH4. © 2007 Elsevier B.V. All rights reserved. Keywords: Nanocomposites; Catalysts; Hydrogen generation; NaBH4; Nickel
1. Introduction The problem of global warming, owing to the greenhouse effect caused by a steep increase in carbon dioxide and other gases, has become a critical issue. Hydrogen is an environmentally friendly solution to this problem. It attracts more and more attention and is going to be an alterative energy source. Many methods for hydrogen generation, such as reforming of natural gas [1,2], coal gasification [3], biomass pyrolysis and gasification [4], electrolytic or photocatalytic water splitting [5,6] and hydrolysis of chemical hydride [7,8], were developed. Among them, hydrolysis of chemical hydride, for instance, NaBH4, was more favorable for its possessing advantages of high hydrogen density, pure hydrogen generation [9], stability in alkaline solution [10], and recycling of the by-products [11]. Hydrogen generation via hydrolysis of NaBH4 is ruled by the following formula: NaBH4 þ 2H2 O ¼ NaBO2 þ 4H2
ð1Þ
The speed of releasing of hydrogen can be raised by decreasing pH of the solution or by adding catalysts [12]. Colloids of novel metal nanoparticles, such as platinum [13,14] and ruthenium [15,16] can be used for rapid hydrogen generation. Some normal metal nanostructure, for example, cobalt [17,18] and nickel [9,19], were also introduced as a catalytic material for hydrolysis of NaBH4. Metal borides, such as cobalt boride [20], were another kind of high performance catalysts for NaBH4 hydrolysis. In this study a novel nanocomposite catalyst was used for hydrogen generation via hydrolysis of NaBH4. In this novel nanocomposite (Ni/Ag/silica), silica was used as a support material, which was coated by silver and nickel nanoparticles. The Ni/Ag/silica nanocomposite catalysts were prepared by different procedures and used directly as catalysts for hydrogen generation. Morphologies and catalytic activities of these nanocomposites were characterized and discussed. 2. Experimental 2.1. Synthesis of Ni/Ag/silica nanocomposite catalysts
⁎ Corresponding author. Tel.: +82 31 330 6688; fax: +82 31 336 6336. E-mail addresses: [email protected] (Y. Chen), [email protected] (H. Kim). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.08.084
Ni/Ag/silica nanocomposite catalysts were prepared by in situ reduction of metal salt on the surface of amine functionalized
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Y. Chen, H. Kim / Materials Letters 62 (2008) 1451–1454
Fig. 1. UV spectra of Ni/Ag/silica nanocomposites.
silica nanospheres. Silica nanospheres were synthesized by modified Stöber method and amine functionalized silica was obtained by following surface modification of silica nanosphere with 3-amino propyl trimethoxylsalane [21]. Silver/silica nanocomposites were prepared using a similar method with the previous report [22], except for using amine group to replace the PVP anchor. Briefly, 10 ml amine functionalized silica was mixed with 1 ml, 10 mM AgNO3 solution (1 wt% Ag relative to silica). Two kinds of reductants, formaldehyde-alkaline solution and sodium borohydride were added to the solution to reduce the silver salt. The formed silver particles tended to attach to the amine functionalized silica nanospheres and formed Ag/silica nanocomposites. The formed nanocomposites were separated by centrifugation and redispersion in 10 ml deionized water for later use. Nickel particles were coated directly on the surface of Ag/ silica nanocomposites by reducing NiCl2 in the Ag/silica colloid solution. 7 ml 10 mM NiCl2 (10 wt% Ni relative to silica) was added to a mixture of 10 ml Ag/silica colloid and sodium borohydride. As a comparison, nickel coating on amine functionalized silica in the absence of silver attaching was also done. 2.2. Catalytic hydrolysis of NaBH4 Three different procedures were used for preparation of nickel nanocomposite catalysts for hydrolysis of NaBH4: (i) nickel nanocomposites prepared by attaching nickel onto amine functionalized silica (Sample Ni(S)), (ii) Ag/silica nanocompo-
sites reduced by formaldehyde (Sample Ni(F)) and (iii) by sodium borohydride (Sample Ni(B)). 10 ml nanocomposite catalyst colloids (containing 4.2 mg Ni) were mixed with 40 ml, 150 mM NaBH4 aqueous solution in a sealed reactor with a pipe on the top which allows the hydrogen gas leading into a collecting bottle filled with water. The reactor was kept at constant temperature of 30 °C in a water bath. The amount of accumulated hydrogen was recorded using Balance Talk system which weighs the amount of water replaced by hydrogen gas. Considering some ability of catalytic hydrolysis of NaBH4, 10 ml amine functionalized silica was used for the same amount of NaBH4 aqueous solution. Self-hydrolysis (SH) of NaBH4 aqueous solution is not negligible since more than 100 ml of hydrogen was generated after 60 min. Effects of silver on the decomposition of NaBH4 was examined by adding 1 ml, 10 mM silver nitrate solution to 49 ml, 150 mM NaBH4 solution. 2.3. Characterization of Ni/Ag/silica nanocomposite catalysts The optical spectra of the catalyst solutions of Ni(S), Ni(F) and Ni(B) were acquired using a Cary 100 UV–Vis spectrophotometer with a 1 cm light path quartz cell. Structure and morphology of the Ni/Ag/silica nanocomposite were examined using a Hitachi S-3500N SEM. 3. Results and discussion Fig. 1 shows the UV–visible absorption spectra of Ni/Ag/silica nanocomposites which were prepared by different procedures as listed in Table 1. Ni(S) displayed no absorption peaks since both of nickel and silica have no absorption in the UV–visible region. On the contrary, after incorporation of 1 wt% of silver nanoparticles, the characteristic peak at around 420 nm appeared. It was noted that the peak of Ni(F) located at 415 nm shifted to 427 nm for Ni(B). These results were caused by the differences in the preparation procedures for Ni/Ag/silica nanocomposites. For Ni(F), silver seeds were reduced by formaldehyde and the formed particles tended to attach to the surface of silica via amine groups uniformly since only 1 wt.% of silver related to silica was added. Ni(B), in which silver is reduced by a rapid reducing agent (NaBH4), however, formed two kinds of silver nanoparticles [23]. One is the tiny silver nuclei formed by rapid reduction, and stabilized by side products (boronates or silver–boron alloys), which were removed by centrifugation. The other is a small portion of silver nanoparticles aggregated from the nuclei and attached on the surface of
Table 1 Performance of Ni/Ag/silica nanocomposite catalysts for hydrogen generation via hydrolysis of NaBH4 Sample name
Procedures
Rate of H2 generation (ml/min)
Rate per unit Ni (ml/min/g Ni)
Conditions
Ni(F)
Ni/Ag/silica with silver reduced by formaldehyde Ni/silica without silver Ni/Ag/silica with silver reduced by NaBH4 Amine functionalized silica Self-hydrolysis AgNO3
10.92
2600
30 °C, 150 mM NaBH4, 10 ml nanocomposites containing 4.2 mg Ni
8.91 5.27
2121 1255
2.27
–
30 °C, 150 mM NaBH4, 10 ml silica
1.31 1.26
– –
30 °C, 150 mM NaBH4 30 °C, 150 mM NaBH4, 1 ml 10 mM AgNO3
Ni(S) Ni(B) Silica SH Silver
Y. Chen, H. Kim / Materials Letters 62 (2008) 1451–1454
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the amine functionalized silica. According to Mie theory and based from the absorption curves shown in Fig. 1, the size of the aggregate silver nanoparticles on the surface of silica is larger for Ni(B) than that of Ni(F). The structure and morphology of the Ni/Ag/silica nanocomposite catalysts were examined using SEM. All nanocomposites prepared by
Fig. 3. Accumulated hydrogen production using different catalysts with 150 mM NaBH4 and 30 °C.
various procedures incorporated with 10 wt% of Ni have similar particle size of about 120 nm. The morphologies, however, were different for Ni(F), Ni(S), and Ni(B). As can be seen from Fig. 2(a), Ni(F) possesses more voids, thus it has higher surface area than Ni(S) and Ni(B). For Ni(B), however, the nanocomposites accumulated in a bulk as shown in Fig. 2(c). This phenomenon was attributed to the formation of uniform silver seeds on the surface of amine functionalized silica. In Ni(B), nickel nanoparticle was attached to the larger silver aggregates and finally formed the aggregated nanocomposites. While in Ni(F), silver salt was reduced by formaldehyde and the formed tiny silver nuclei distributed uniformly on the amine functionalized silica. These nuclei on the surface of silica play a role as the seed for the growth of nickel particles. Thus the formed nanocomposite, Ni(F) has more voids and high surface area. The differences in morphologies of Ni/ Ag/silica nanocomposites hold much influence on the catalytic activities of hydrolysis of NaBH4 for hydrogen generation which will be discussed further. Catalytic activities of the Ni/Ag/silica nanocomposites for hydrogen generation from hydrolysis of NaBH4 were investigated and the results were shown in Fig. 3 and Table 1. NaBH4 aqueous solution is not stable since it produces hydrogen gas slowly at room temperature. In industrial application, alkali is added to stabilize the solution. Comparing the two curves of ‘SH’ and ‘Silver’, it can be concluded that silver has little effect on the hydrolysis of NaBH4. Although silica itself had some activity for hydrolysis of NaBH4, it was not good enough for the reaction as compared with Ni/Ag/silica nanocomposites. The catalytic activities of Ni/Ag/silica nanocomposites also held some differences because of shifting structure and morphologies. Ni(B) had lower rate of hydrogen generation than that of Ni(S) because of aggregation of nanocomposites. On the contrary, Ni(F) possessed the highest rate of hydrogen generation due to the formation of loosen and void-rich structures. The hydrogen generation rate as high as 2600 ml/min/g Ni notes that Ni(F) is a competitive catalytic material for hydrogen generation from hydrolysis of NaBH4.
4. Conclusion
Fig. 2. SEM images of Ni/Ag/silica nanocomposite catalysts prepared by different procedures. (a) Ni(F), (b) Ni(S), and (c) Ni(B).
The Ni/Ag/silica nanocomposite catalysts were prepared by three different procedures and used directly as catalysts for hydrogen generation. Catalytic activities of these catalysts hold much difference for shifting their structure and morphologies. Hydrogen generation with a rate as high as 2600 ml/min/g Ni was reached using a novel nanocomposite catalyst from hydrolysis of NaBH4 solution.
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Acknowledgement This work was financially supported by BK21 program of Korea. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
R.J. Farrauto, Appl. Catal., B Environ. 56 (2005) 3–7. A. Heinzel, B. Vogel, P. Hubner, J. Power Sources 105 (2002) 202–207. G.J. Stiegel, M. Ramezan, Int. J. Coal Geol. 65 (2006) 173–190. E.E. Iojoiu, M.E. Domine, T. Davidian, N. Guilhaume, C. Mirodatos, Appl. Catal., A Gen. 323 (2007) 147–161. H. De Battista, R.J. Mantz, F. Garelli, J. Power Sources 155 (2006) 478–486. N.A. Kelly, T.L. Gibson, Int. J. Hydrogen Energy 31 (2006) 1658–1673. S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, N.C. Spencer, M.T. Kelly, P.J. Petillo, M. Binder, Int. J. Hydrogen Energy 25 (2000) 969–975. J.-H. Kim, K.-T. Kim, Y.-M. Kang, H.-S. Kim, M.-S. Song, Y.-J. Lee, P.S. Lee, J.-Y. Lee, J. Alloys Compd. 379 (2004) 222–227. J.-H. Kim, H. Lee, S.-C. Han, H.-S. Kim, M.-S. Song, J.-Y. Lee, Int. J. Hydrogen Energy 29 (2004) 263–267.
[10] J.A. Ritter, A.D. Ebner, J. Wang, R. Zidan, Mater. Today 6 (2003) 18–23. [11] D.L. Calabretta, B.R. Davis, J. Power Sources 164 (2007) 782–791. [12] Clifford M. Kaufman, B. Sen, J. Chem. Soc., Dalton Trans. (1985) 307–313. [13] Y. Kojima, K.-i. Suzuki, K. Fukumoto, M. Sasaki, T. Yamamoto, Y. Kawai, H. Hayashi, Int. J. Hydrogen Energy 27 (2002) 1029–1034. [14] C. Wu, H. Zhang, B. Yi, Catal. Today 93-95 (2004) 477–483. [15] S. Ozkar, M. Zahmakiran, J. Alloys Compd. 404-406 (2005) 728–731. [16] J.S. Zhang, W.N. Delgass, T.S. Fisher, J.P. Gore, J. Power Sources 164 (2007) 772–781. [17] S.U. Jeong, R.K. Kim, E.A. Cho, H.J. Kim, S.W. Nam, I.H. Oh, S.A. Hong, S.H. Kim, J. Power Sources 144 (2005) 129–134. [18] W. Ye, H. Zhang, D. Xu, L. Ma, B. Yi, J. Power Sources 164 (2007) 544–548. [19] D. Hua, Y. Hanxi, A. Xinping, C. Chuansin, Int. J. Hydrogen Energy 28 (2003) 1095–1100. [20] C. Wu, F. Wu, Y. Bai, B. Yi, H. Zhang, Mater. Lett. 59 (2005) 1748–1751. [21] S.L. Westcott, S.J. Oldenburg, T.R. Lee, N.J. Halas, Langmuir 14 (1998) 5396–5401. [22] Y. Chen, H. Kim, Mater. Lett. (2007), doi:10.1016/j.matlet.2007.03.100. [23] A.B.R. Mayer, W. Grebner, R. Wannemacher, J. Phys. Chem., B 104 (2000) 7278–7285.
Materials Letters 62 (2008) 1451 – 1454 www.elsevier.com/locate/matlet
Ni/Ag/silica nanocomposite catalysts for hydrogen generation from hydrolysis of NaBH4 solution Yingbo Chen, Hern Kim ⁎ Department of Environmental Engineering and Biotechnology, Myongji University, San 38-2 Namdong, Yongin, Kyonggi-do 449-728, Republic of Korea Received 4 June 2007; accepted 28 August 2007 Available online 6 September 2007
Abstract Ni/Ag/silica nanocomposite catalysts were prepared by three procedures—nickel coated to amine functionalized silica directly, nickel coated on the surface of Ag/silica nanocomposites reduced by formaldehyde and NaBH4, respectively. The properties and morphologies of the Ni/Ag/silica nanocomposite catalysts were studied by UV–Visible spectra and scanning electron microscopy. The novel catalysts were applied for hydrogen generation from hydrolysis of NaBH4. A rate of hydrogen generation per unit nickel as high as 2600 ml/min/g Ni was obtained with 150 mM NaBH4 at 30 °C, which notes that these nanocomposites can be used as a competitive catalytic material for hydrogen generation via hydrolysis of NaBH4. © 2007 Elsevier B.V. All rights reserved. Keywords: Nanocomposites; Catalysts; Hydrogen generation; NaBH4; Nickel
1. Introduction The problem of global warming, owing to the greenhouse effect caused by a steep increase in carbon dioxide and other gases, has become a critical issue. Hydrogen is an environmentally friendly solution to this problem. It attracts more and more attention and is going to be an alterative energy source. Many methods for hydrogen generation, such as reforming of natural gas [1,2], coal gasification [3], biomass pyrolysis and gasification [4], electrolytic or photocatalytic water splitting [5,6] and hydrolysis of chemical hydride [7,8], were developed. Among them, hydrolysis of chemical hydride, for instance, NaBH4, was more favorable for its possessing advantages of high hydrogen density, pure hydrogen generation [9], stability in alkaline solution [10], and recycling of the by-products [11]. Hydrogen generation via hydrolysis of NaBH4 is ruled by the following formula: NaBH4 þ 2H2 O ¼ NaBO2 þ 4H2
ð1Þ
The speed of releasing of hydrogen can be raised by decreasing pH of the solution or by adding catalysts [12]. Colloids of novel metal nanoparticles, such as platinum [13,14] and ruthenium [15,16] can be used for rapid hydrogen generation. Some normal metal nanostructure, for example, cobalt [17,18] and nickel [9,19], were also introduced as a catalytic material for hydrolysis of NaBH4. Metal borides, such as cobalt boride [20], were another kind of high performance catalysts for NaBH4 hydrolysis. In this study a novel nanocomposite catalyst was used for hydrogen generation via hydrolysis of NaBH4. In this novel nanocomposite (Ni/Ag/silica), silica was used as a support material, which was coated by silver and nickel nanoparticles. The Ni/Ag/silica nanocomposite catalysts were prepared by different procedures and used directly as catalysts for hydrogen generation. Morphologies and catalytic activities of these nanocomposites were characterized and discussed. 2. Experimental 2.1. Synthesis of Ni/Ag/silica nanocomposite catalysts
⁎ Corresponding author. Tel.: +82 31 330 6688; fax: +82 31 336 6336. E-mail addresses: [email protected] (Y. Chen), [email protected] (H. Kim). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.08.084
Ni/Ag/silica nanocomposite catalysts were prepared by in situ reduction of metal salt on the surface of amine functionalized
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Y. Chen, H. Kim / Materials Letters 62 (2008) 1451–1454
Fig. 1. UV spectra of Ni/Ag/silica nanocomposites.
silica nanospheres. Silica nanospheres were synthesized by modified Stöber method and amine functionalized silica was obtained by following surface modification of silica nanosphere with 3-amino propyl trimethoxylsalane [21]. Silver/silica nanocomposites were prepared using a similar method with the previous report [22], except for using amine group to replace the PVP anchor. Briefly, 10 ml amine functionalized silica was mixed with 1 ml, 10 mM AgNO3 solution (1 wt% Ag relative to silica). Two kinds of reductants, formaldehyde-alkaline solution and sodium borohydride were added to the solution to reduce the silver salt. The formed silver particles tended to attach to the amine functionalized silica nanospheres and formed Ag/silica nanocomposites. The formed nanocomposites were separated by centrifugation and redispersion in 10 ml deionized water for later use. Nickel particles were coated directly on the surface of Ag/ silica nanocomposites by reducing NiCl2 in the Ag/silica colloid solution. 7 ml 10 mM NiCl2 (10 wt% Ni relative to silica) was added to a mixture of 10 ml Ag/silica colloid and sodium borohydride. As a comparison, nickel coating on amine functionalized silica in the absence of silver attaching was also done. 2.2. Catalytic hydrolysis of NaBH4 Three different procedures were used for preparation of nickel nanocomposite catalysts for hydrolysis of NaBH4: (i) nickel nanocomposites prepared by attaching nickel onto amine functionalized silica (Sample Ni(S)), (ii) Ag/silica nanocompo-
sites reduced by formaldehyde (Sample Ni(F)) and (iii) by sodium borohydride (Sample Ni(B)). 10 ml nanocomposite catalyst colloids (containing 4.2 mg Ni) were mixed with 40 ml, 150 mM NaBH4 aqueous solution in a sealed reactor with a pipe on the top which allows the hydrogen gas leading into a collecting bottle filled with water. The reactor was kept at constant temperature of 30 °C in a water bath. The amount of accumulated hydrogen was recorded using Balance Talk system which weighs the amount of water replaced by hydrogen gas. Considering some ability of catalytic hydrolysis of NaBH4, 10 ml amine functionalized silica was used for the same amount of NaBH4 aqueous solution. Self-hydrolysis (SH) of NaBH4 aqueous solution is not negligible since more than 100 ml of hydrogen was generated after 60 min. Effects of silver on the decomposition of NaBH4 was examined by adding 1 ml, 10 mM silver nitrate solution to 49 ml, 150 mM NaBH4 solution. 2.3. Characterization of Ni/Ag/silica nanocomposite catalysts The optical spectra of the catalyst solutions of Ni(S), Ni(F) and Ni(B) were acquired using a Cary 100 UV–Vis spectrophotometer with a 1 cm light path quartz cell. Structure and morphology of the Ni/Ag/silica nanocomposite were examined using a Hitachi S-3500N SEM. 3. Results and discussion Fig. 1 shows the UV–visible absorption spectra of Ni/Ag/silica nanocomposites which were prepared by different procedures as listed in Table 1. Ni(S) displayed no absorption peaks since both of nickel and silica have no absorption in the UV–visible region. On the contrary, after incorporation of 1 wt% of silver nanoparticles, the characteristic peak at around 420 nm appeared. It was noted that the peak of Ni(F) located at 415 nm shifted to 427 nm for Ni(B). These results were caused by the differences in the preparation procedures for Ni/Ag/silica nanocomposites. For Ni(F), silver seeds were reduced by formaldehyde and the formed particles tended to attach to the surface of silica via amine groups uniformly since only 1 wt.% of silver related to silica was added. Ni(B), in which silver is reduced by a rapid reducing agent (NaBH4), however, formed two kinds of silver nanoparticles [23]. One is the tiny silver nuclei formed by rapid reduction, and stabilized by side products (boronates or silver–boron alloys), which were removed by centrifugation. The other is a small portion of silver nanoparticles aggregated from the nuclei and attached on the surface of
Table 1 Performance of Ni/Ag/silica nanocomposite catalysts for hydrogen generation via hydrolysis of NaBH4 Sample name
Procedures
Rate of H2 generation (ml/min)
Rate per unit Ni (ml/min/g Ni)
Conditions
Ni(F)
Ni/Ag/silica with silver reduced by formaldehyde Ni/silica without silver Ni/Ag/silica with silver reduced by NaBH4 Amine functionalized silica Self-hydrolysis AgNO3
10.92
2600
30 °C, 150 mM NaBH4, 10 ml nanocomposites containing 4.2 mg Ni
8.91 5.27
2121 1255
2.27
–
30 °C, 150 mM NaBH4, 10 ml silica
1.31 1.26
– –
30 °C, 150 mM NaBH4 30 °C, 150 mM NaBH4, 1 ml 10 mM AgNO3
Ni(S) Ni(B) Silica SH Silver
Y. Chen, H. Kim / Materials Letters 62 (2008) 1451–1454
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the amine functionalized silica. According to Mie theory and based from the absorption curves shown in Fig. 1, the size of the aggregate silver nanoparticles on the surface of silica is larger for Ni(B) than that of Ni(F). The structure and morphology of the Ni/Ag/silica nanocomposite catalysts were examined using SEM. All nanocomposites prepared by
Fig. 3. Accumulated hydrogen production using different catalysts with 150 mM NaBH4 and 30 °C.
various procedures incorporated with 10 wt% of Ni have similar particle size of about 120 nm. The morphologies, however, were different for Ni(F), Ni(S), and Ni(B). As can be seen from Fig. 2(a), Ni(F) possesses more voids, thus it has higher surface area than Ni(S) and Ni(B). For Ni(B), however, the nanocomposites accumulated in a bulk as shown in Fig. 2(c). This phenomenon was attributed to the formation of uniform silver seeds on the surface of amine functionalized silica. In Ni(B), nickel nanoparticle was attached to the larger silver aggregates and finally formed the aggregated nanocomposites. While in Ni(F), silver salt was reduced by formaldehyde and the formed tiny silver nuclei distributed uniformly on the amine functionalized silica. These nuclei on the surface of silica play a role as the seed for the growth of nickel particles. Thus the formed nanocomposite, Ni(F) has more voids and high surface area. The differences in morphologies of Ni/ Ag/silica nanocomposites hold much influence on the catalytic activities of hydrolysis of NaBH4 for hydrogen generation which will be discussed further. Catalytic activities of the Ni/Ag/silica nanocomposites for hydrogen generation from hydrolysis of NaBH4 were investigated and the results were shown in Fig. 3 and Table 1. NaBH4 aqueous solution is not stable since it produces hydrogen gas slowly at room temperature. In industrial application, alkali is added to stabilize the solution. Comparing the two curves of ‘SH’ and ‘Silver’, it can be concluded that silver has little effect on the hydrolysis of NaBH4. Although silica itself had some activity for hydrolysis of NaBH4, it was not good enough for the reaction as compared with Ni/Ag/silica nanocomposites. The catalytic activities of Ni/Ag/silica nanocomposites also held some differences because of shifting structure and morphologies. Ni(B) had lower rate of hydrogen generation than that of Ni(S) because of aggregation of nanocomposites. On the contrary, Ni(F) possessed the highest rate of hydrogen generation due to the formation of loosen and void-rich structures. The hydrogen generation rate as high as 2600 ml/min/g Ni notes that Ni(F) is a competitive catalytic material for hydrogen generation from hydrolysis of NaBH4.
4. Conclusion
Fig. 2. SEM images of Ni/Ag/silica nanocomposite catalysts prepared by different procedures. (a) Ni(F), (b) Ni(S), and (c) Ni(B).
The Ni/Ag/silica nanocomposite catalysts were prepared by three different procedures and used directly as catalysts for hydrogen generation. Catalytic activities of these catalysts hold much difference for shifting their structure and morphologies. Hydrogen generation with a rate as high as 2600 ml/min/g Ni was reached using a novel nanocomposite catalyst from hydrolysis of NaBH4 solution.
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Y. Chen, H. Kim / Materials Letters 62 (2008) 1451–1454
Acknowledgement This work was financially supported by BK21 program of Korea. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
R.J. Farrauto, Appl. Catal., B Environ. 56 (2005) 3–7. A. Heinzel, B. Vogel, P. Hubner, J. Power Sources 105 (2002) 202–207. G.J. Stiegel, M. Ramezan, Int. J. Coal Geol. 65 (2006) 173–190. E.E. Iojoiu, M.E. Domine, T. Davidian, N. Guilhaume, C. Mirodatos, Appl. Catal., A Gen. 323 (2007) 147–161. H. De Battista, R.J. Mantz, F. Garelli, J. Power Sources 155 (2006) 478–486. N.A. Kelly, T.L. Gibson, Int. J. Hydrogen Energy 31 (2006) 1658–1673. S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, N.C. Spencer, M.T. Kelly, P.J. Petillo, M. Binder, Int. J. Hydrogen Energy 25 (2000) 969–975. J.-H. Kim, K.-T. Kim, Y.-M. Kang, H.-S. Kim, M.-S. Song, Y.-J. Lee, P.S. Lee, J.-Y. Lee, J. Alloys Compd. 379 (2004) 222–227. J.-H. Kim, H. Lee, S.-C. Han, H.-S. Kim, M.-S. Song, J.-Y. Lee, Int. J. Hydrogen Energy 29 (2004) 263–267.
[10] J.A. Ritter, A.D. Ebner, J. Wang, R. Zidan, Mater. Today 6 (2003) 18–23. [11] D.L. Calabretta, B.R. Davis, J. Power Sources 164 (2007) 782–791. [12] Clifford M. Kaufman, B. Sen, J. Chem. Soc., Dalton Trans. (1985) 307–313. [13] Y. Kojima, K.-i. Suzuki, K. Fukumoto, M. Sasaki, T. Yamamoto, Y. Kawai, H. Hayashi, Int. J. Hydrogen Energy 27 (2002) 1029–1034. [14] C. Wu, H. Zhang, B. Yi, Catal. Today 93-95 (2004) 477–483. [15] S. Ozkar, M. Zahmakiran, J. Alloys Compd. 404-406 (2005) 728–731. [16] J.S. Zhang, W.N. Delgass, T.S. Fisher, J.P. Gore, J. Power Sources 164 (2007) 772–781. [17] S.U. Jeong, R.K. Kim, E.A. Cho, H.J. Kim, S.W. Nam, I.H. Oh, S.A. Hong, S.H. Kim, J. Power Sources 144 (2005) 129–134. [18] W. Ye, H. Zhang, D. Xu, L. Ma, B. Yi, J. Power Sources 164 (2007) 544–548. [19] D. Hua, Y. Hanxi, A. Xinping, C. Chuansin, Int. J. Hydrogen Energy 28 (2003) 1095–1100. [20] C. Wu, F. Wu, Y. Bai, B. Yi, H. Zhang, Mater. Lett. 59 (2005) 1748–1751. [21] S.L. Westcott, S.J. Oldenburg, T.R. Lee, N.J. Halas, Langmuir 14 (1998) 5396–5401. [22] Y. Chen, H. Kim, Mater. Lett. (2007), doi:10.1016/j.matlet.2007.03.100. [23] A.B.R. Mayer, W. Grebner, R. Wannemacher, J. Phys. Chem., B 104 (2000) 7278–7285.