- Email: [email protected]
Hydrogen storage in platinum loaded single-walled carbon nanotubes
international journal of hydrogen energy xxx (xxxx) xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Hydrogen storage in platinum loaded single-walled carbon nanotubes Anshu Sharma Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
highlights A simple and effective method to load Pt on SWNT is presented. Morphological changes in SWNT after loading of Pt is discussed. Investigation on thermal stability of SWNT with and without Pt loading. H2 storage capacities of SWNT and SWNT/Pt at 77 K and RT are discussed.
article info
abstract
Article history:
To study the hydrogen storage capacity, platinum (Pt) nanoparticles were deposited on
Received 21 March 2019
single-walled carbon nanotubes (SWNT) using hexachloroplatinic acid (H2PtCl6$6H2O) as a
Received in revised form
precursor. To verify Pt deposition on the surface of the SWNT, a Transmission Electron
30 April 2019
Microscope (TEM) was used to obtain surface morphology. The TEM images show that Pt
Accepted 4 September 2019
nanoparticles were homogeneously distributed on the surface of SWNT. Commercial
Available online xxx
SWNT were also used to compare the results. Thermal Gravimetric Analysis at heating rate of 5 C/min is measured for pure SWNT and Pt loaded SWNT. Before hydrogen storage
Keywords:
measurements these samples were reduced in 10% of H2 in Ar, flowing at 900 C in a
Single-walled carbon nanotubes
tubular furnace for 1 hour. Hydrogen storage capacity of these SWNT was investigated
Platinum nanoparticles
under 25 bar pressure and room temperature as well as liquid nitrogen temperature.
Hydrogen storage
© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Physisorption
Introduction Hydrogen has the highest energy density 120 MJ/kg over all possible fuels and this value is three times higher than gasoline. It is most abundant and an environmentally friendly energy carrier as water is its end combustion product. Regardless of all advantages, its low volumetric density (0.0899 kg/m3) at ambient conditions make it commercially limited [1,2]. Therefore hydrogen storage in a squeezed, reasonable and safer way is major technical barrier which prevents its widespread implementation as a substitute
energy carrier [3e5]. For hydrogen storage several methods including high-pressure hydrogen, liquid hydrogen, physisorption and chemisorption have been proposed. Hydrogen storage in the form of metal hydrides, compressed gas or hydrogen liquefaction possesses unadorned disadvantages [6e10]. These downsides have induced new storage conceptions as physical adsorption of hydrogen on nanomaterials. Porous materials such as metal organic frameworks has become the interest of scientific community as they shows a lot of advantages over above mentioned methods due to their fast adsorption/desorption kinetics [11e15]. Particularly
E-mail address: [email protected]. https://doi.org/10.1016/j.ijhydene.2019.09.025 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
2
international journal of hydrogen energy xxx (xxxx) xxx
unique carbon materials, such as carbon nanotubes (CNT), has considered as an auspicious contender for gas adsorption. Carbon is among the very few materials which are light and solid at room temperature (RT). CNT has many advantages like low-cost availability, heat resistance, reversibility, large thermal and chemical stability. In bundles of CNT different adsorption sites are possible for hydrogen such as interstitial networks between the single-walled carbon nanotubes (SWNT) in a bundle, pore of the SWNT and on the external surface of the tube wall or in the grooves formed at the connection between adjacent tubes [16]. Physisorption which is responsible for the hydrogen adsorption in CNT is based on the vander Waals forces between adsorbate and adsorbent. Low hydrogen storage capacities of nanomaterials at ambient conditions [17,18] indicates that at RT interaction due to vander Waals forces is as small as gas molecules have thermal energy on surface of the adsorbent. Therefore reduction in the temperature of the system induces the interaction between adsorbent and gas molecule. Physisorption is considered as a very capable method for hydrogen storage as it is based on the vander Waals forces between adsorbent and adsorbate due to which it shows fast kinetics [19,20]. To increase the hydrogen storage capacities numerous methods such as metal doping and ligand exchange have been reported. It is reported that metal precursor loaded on CNT surface exhibit an upgraded catalytic activity. A robust interaction between nanomaterial and metal precursor is essential for preparation of highly dispersed and stable catalyst. Before loading of metal catalyst particle on the surface of CNT its pretreatments such as acid functionalization introduces active sites on its surface. These pretreatments are also helpful to remove fullerene-like caps or the metal clusters at the ends of the tubes without destroying the nanotubes which allow easy access of the hydrogen to the tube interior. Properties of the functional groups, their dispersion and concentration also impact the dispersion of noble metals. Several experimental methods are introduced in CNTs loaded with metal nanoparticles which include Fe, Co, Mg, Ag, Pt, Li and Pd [21e25]. In this paper, for dissociation of hydrogen molecules and its subsequent adsorption with the possibility of Pt as a catalyst loaded on SWNT at 77 K and RT has been studied.
oil bath at 80 C for 18 h using constant stirring. Then, this acid treated product was cooled up to RT, filtered and washed with deionized water till the remained mixture grasped pH 7 then this filtrate was dried for 2 h at 100 C in an air oven. This acid treated SWNT powder used for further step. Then loading of Pt nanoparticles on the surface of SWNT were performed using a simple and efficient chemical root method. In this procedure, H2PtCl6 (10 mL) were added to the ethylene glycol (20 mL) under constant stirring to ensure the complete solubility of H2PtCl6 then acid treated SWNT (400 mg) were dispersed in to the above solution and ultrasonication was performed about 30 min. Further, this reaction mixture was stirred in an oil bath for 4 h at 120 C. Then, this mixture was filtered and washed with deionized water till filtrate reached pH7 and extracted by centrifugation using at 4000 rpm. This prepared soot was then dried in an air oven for 12 h at 80 C. In this way loading of Pt nanoparticles on the surface of SWNT was achieved [26].
Characterization techniques Transmission Electron Miicroscope (TEM) was used to investigate the morphology, size and shape of the samples. A high resolution TEM (JEOL JEM-2010F) at 200 kV was used to record the TEM images. A carbon-coated copper grid with 300 meshes was used to prepare a sample. Thermal Gravimetric Analysis (TGA) was carried out in a thermogravimetric analyzer Hitachi DSC7020. Measurements were performed in an alumina pans with heating rate of 5 C/min in air atmosphere. The final mass of the sample ranged from 5 to 12 mg. Hydrogen adsorption measurements are performed using an automated Sie-vert’s type apparatus (Setaram-HyEnergy PCT-Pro-2000) equipped with a microdoser from HyEnergy. To control the temperature, the sample was submerged in a thermal bath with liquid nitrogen (77 K) or water (300 K). The amounts of used sample are approximately 100 mg and 150 mg for SWNT and SWNT/Pt respectively.
Results and discussion TEM
Experimental details Chemicals Chloroplatinic Acid 8 wt% in water (Sigma Aldrich, Germany) and large surface area SWNT having length 5e35 mm, diameter ~1e2 nm with purity >95% (US Research Nanomaterials Inc., TX, USA) were used in this experiment. Chemical reagents such as carboxylic acid, nitric acid, ethanol etc were of commercial grade and were used as purchased.
Synthesis of SWNT/Pt nanocomposites First of all, as purchased SWNT was functionalized using carboxylic acid. In this process as purchased SWNT (500 mg) was dispersed in 25 ml of concentrated HNO3 and refluxed in
TEM measurements were carried out to measure the location, distribution and particle size of Pt nanoparticles. The as prepared SWNT/Pt nanocomposites were investigated by TEM. Fig. 1 shows the TEM image contrast of pure SWNT and SWNT/Pt composites i.e. after loading of Pt nanoparticles on SWNT. TEM images indicate that the Pt nanoparticles which are dispersed on the surface of the SWNT having an average size of 20e30 nm and do not agglomerate with each other to form a large cluster. TEM images also implies that Pt nanoparticles loaded directly on surface defect sites and pores and no single Pt nanoparticle is resolved in the TEM images which evident the strong bonding between Pt atoms and carbon atoms at the defects. Therefore above presented TEM images shows the efficiency of a simple method to load Pt nanoparticles on the surfaces of SWNT.
Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
3
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 1 e TEM images of (a) SWNT (b) SWNT/Pt. It is cleared from Fig. 2 that as purchased SWNT and Pt loaded SWNT are considerably less stable at high temperature approximate 800 C and 600 C respectively. Here TGA measurements were performed to characterize the stability of SWNT and SWNT/Pt nanocomposite toward hightemperature.
(a) SWNT (b) SWNT/Pt
100
95
Weight (%)
(a) 90
Hydrogen adsorption 85
80
(b) 75 0
200
400
600
800
1000
Temperature (oC)
Fig. 2 e TGA of (a) SWNT and (b) SWNT/Pt.
TGA Determination of the amount of loaded Pt nanoparticles catalyst on the surfaces of SWNT was analyzed by TGA in an air atmosphere. It is a simple analytical technique that is frequently used to determine the decomposition temperature of the CNT.
0.60
(a)SWNT at 77K
Adsorption Desorption
0.55
Figs. 3 and 4 shows the hydrogen adsorption/desorption analyses of as purchased SWNT and SWNT/Pt at 77 K and RT respectively. The measured isotherm shows no saturation at RT. At low temperature a slight increase in adsorption can be observed. At low temperature no saturation of the pressure isotherms can be determined at pressure up to 25 bar. The adsorption reached 0.55e0.60 wt% at 77 K and 25 bar in the case of pure SWNT but as Pt is loaded in SWNT adsorption isotherm reached 0.65e0.70 wt% at 77 K and 25 bar which is greater than pure SWNT. This indicates that the high pressure adsorption is confirmed in SWNT but very high values could not be reproduced. The adsorption occurs due to attractive potential of the pore walls [27,28]. After loading Pt catalyst hydrogen could be physisorbed on SWNT exposed surfaces. Experimental results shown here indicated that at cryogenic temperatures the hydrogen adsorption in the interstitial sites of SWNT bundles
0.020
(b)SWNT at RT
Adsorption Desorption
0.45
Absolute H2 uptake (wt%)
Absolute H2 uptake (wt%)
0.50
0.015
0.40 0.35
0.010
0.30 0.25
0.005
0.20 0.15 0.10
0.000
0.05 0.00 0
5
10
15
Pressure (bar)
20
25
-0.005
0
10
20
30
Pressure (bar)
Fig. 3 e H2 adsorption/desorption isotherms of (a) SWNT at 77 K (b) SWNT at RT. Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
4
international journal of hydrogen energy xxx (xxxx) xxx
0.70
Adsorption Desorption
0.65 0.60
(a)SWNT/Pt at 77K
0.020
(b)SWNT/Pt at RT
Adsorption Desorption
0.018
Absolute H2uptake (wt%)
AbsoluteH2 uptake (wt%)
0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 -0.05
0.016 0.014 0.012 0.010 0.008 0.006 0.004
0
5
10
Pressure (bar)
15
20
25
0
10
Pressure (bar)
20
30
Fig. 4 e H2 adsorption/desorption isotherms of (a) SWNT/Pt at 77 K (b) SWNT/Pt at RT.
possessing a very wide tube diameter and extreme separation could not sufficient to achieve the gravimetric hydrogen storage for DOE target [29].
Conclusion A facile method to load Pt catalysis on SWNT is devised successfully. This study highlights a very simple but efficient synthesis approach for high loading of Pt on SWNT with uniform dispersion. Through the acid treatment large quantities of homogeneously distributed active sites can be generated for anchoring Pt nanoparticles. Physical characterizations revealed that Pt nanoparticles were successfully deposited on the surface of SWNT with a very good density. CNT samples, including SWNT and Pt loaded SWNT were used for hydrogen storage purpose by a gravimetric measurement method. Hydrogen storage capacity of these samples were found less than 1 wt% in both of the cases having conditions of hydrogen gas pressure 25 bar at 77 K and 25 bar at RT. These results suggest that high pressure hydrogen storage is confirmed in SWNT but very high values could not be reproduced. Therefore it is concluded that hydrogen storage capacity of SWNT is far below the DOE targets and it is unfeasible for on-board hydrogen uptake systems. In the other side, for significantly improving their hydrogen storage capacity and kinetics an effective additive can be used in SWNT.
Acknowledgements The author gratefully acknowledges the financial support of the Department of Science and Technology, Ministry of Science and Technology, Govt. of India under women scientists scheme (WOS-A) grant SR/WOS-A/PS-62/2013. Author is highly thankful to Max Planck Institute for the Structure and Dynamics of Matter, Germany for providing experimental facilities for sample preparation and Max Planck Institute for Intelligent System, Stuttgart, Germany for providing hydrogen storage measurements under Max Planck-India mobility grant supported by Max Planck Society, Germany and Indo-German Science and Technology Centre, Department of Science and Technology, Ministry of Science and Technology, Govt. of India.
references
[1] Dillon AC, Heben MJ. Hydrogen storage using carbon adsorbents: past, present and future. Appl Phys A 2001;72:133e42. [2] Wang L, Yang RT. New sorbents for hydrogen storage by hydrogen spillover-A review. Energy Environ Sci 2008;1:268e79. [3] Yurum Y, Taralp A, Veziroglu TN. Storage of hydrogen in nanostructured carbon materials. Int J Hydrogen Energy 2009;34(9):3784e98. [4] De La Casa-Lillo MA, Lamari-Darkrim F, Cazorla Amoros D, Linares Solano A. Hydrogen storage in activated carbons and activated carbon fibers. J Phys Chem B 2002;106:10930e4. [5] Midilli A, Ay M, Dincer I, Rosen MA. On hydrogen and hydrogen energy strategies: I: current status and needs. Renew Sustain Energy Rev 2005;9(3):255e71. [6] Broom DP, Webb CJ, Hurst KE, Parilla PA, Gennett T, Brown CM, Zacharia R, Tylianakis E, Klontzas E, Froudakis GE, Steriotis TA, Trikalitis PN, Anton DL, Hardy B, Tamburello D, Corgnale C, Van Hassel BA, Cossement D, Chahine R, Hirscher M. Outlook and challenges for hydrogen storage in nanoporous materials. Appl Phys A 2016;122:151 (1e21). [7] Mehrabi M, Parvin P, Reyhani A, Mortazavi SZ. Hydrogen storage in multi-walled carbon nanotubes decorated with palladium nanoparticles using laser ablation/chemical reduction methods. Mater Res Express 2017;4:095030. [8] Tellez Juarez MC, Fierro V, Zhao W, Fernandez Huerta N, Izquierdo MT, Reguera E, Celzard A. Hydrogen storage in activated carbons produced from coals of different ranks: effect of oxygen content. Int J Hydrogen Energy 2014;39(10). 4996e02. [9] Joo SH, Choi SJ, Oh I, Kwak J, Liu Z, Terasaki O, Ryoo R. Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles. Nature 2001;412:169e72. [10] Zhao W, Fierro V, Fernandez Huerta N, Izquierdo MT, Celzard A. Hydrogen uptake of high surface area-activated carbons doped with nitrogen. Int J Hydrogen Energy 2013;38(25):10453e60. [11] Gogotsi Y, Portet C, Osswald S, Simmons JM, Yildirim T, Laudisio G, Fischer JE. Importance of pore size in highpressure hydrogen storage by porous carbons. Int J Hydrogen Energy 2009;34(15):6314e9. [12] Yang SJ, Im JH, Nishihara H, Jung H, Lee K, Kyotani T, Park CR. General relationship between hydrogen
Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
international journal of hydrogen energy xxx (xxxx) xxx
[13] [14]
[15]
[16] [17]
[18]
[19] [20]
[21]
adsorption capacities at 77 and 298 K and pore characteristics of the porous adsorbents. J Phys Chem C 2012;116(19):10529e40. Broom DP, Hirscher M. Irreproducibility in hydrogen storage material research. Energy Environ Sci 2016;9(11):3368e80. Liu X, Zhang C, Geng Z, Cai M. High-pressure hydrogen storage and optimizing fabrication of corncob-derived activated carbon. Microporous Mesoporous Mater 2014;194:60e5. Oh H, Gennett T, Atanassov P, Kurttepeli M, Bals S, Hurst KE, Hirscher M. Hydrogen adsorption properties of platinum decorated hierarchically structured templated carbons. Microporous Mesoporous Mater 2013;177:66e74. Hirscher M, Becher M. Hydrogen storage in carbon nanotubes. J Nanosci Nanotechnol 2003;3:3e17. Liu Z, Xue Q, Ling C, Yan Z, Zheng J. Hydrogen storage and release by bending carbon nanotubes. Comput Mater Sci 2013;68:121e6. Nasruddin N, Kosasih EA, Kurniawan B, Supriyadi S, Zulkarnain IA. Optimization of hydrogen storage capacity by physical adsorption on open-ended single-walled carbon nanotube as diameter function. Int J Technol 2016;2:264e73. Bhatia SK, Myers AL. Optimum conditions for adsorptive storage. Langmuir 2006;22(4):1688e700. Barghi SH, Tsotsis TT, Sahimi M. Chemisorption, physisorption and hysteresis during hydrogen storage in carbon nanotubes. Int J Hydrogen Energy 2014;39:1390e7. Li J, Zhang H, Yang G. Ultrahigh-capacity molecular hydrogen storage of a lithium-decorated boron monolayer. J Phys Chem C 2015;119:19681e8.
5
[22] Li Y, Yang RT. Hydrogen storage on platinum nanoparticles doped on superactivated carbon. J Phys Chem C 2007;111:11086e94. [23] Adjizian JJ, Marco PD, Martinez IS, Mel AAE, Snyders R, Gengler RYN, Rudolf P, Ke X, Tendeloo GV, Bittencourt C, Ewels CP. Platinum and palladium on carbon nanotubes: experimental and theoretical studies. Chem Phys Lett 2013;571:44e8. [24] Sevilla M, Fuertes AB, Mokaya R. Preparation and hydrogen storage capacity of highly porous activated carbon materials derived from polythiophene. Int J Hydrogen Energy 2011;36(24):15658e63. [25] Georgakis M, Stavropoulos G, Sakellaropoulos GP. Molecular dynamics study of hydrogen adsorption in carbonaceous microporous materials and the effect of oxygen functional groups. Int J Hydrogen Energy 2007;32(12):1999e2004. [26] Sharma A, Andreas R, Nehra SP. Synthesis of SWNT/Pt nanocomposites for their effective role in hydrogen storage applications. AIP Conf Proc 2018;1953:030148. [27] Govind Sethia G, Sayari A. Activated carbon with optimum pore size distribution for hydrogen storage. Carbon 2016;99:289e94. [28] Broom DP, Webb CJ. Pitfalls in the characterization of the hydrogen sorption properties of materials. Int J Hydrogen Energy 2017;42(49):29320e43. [29] DoE, Target Explanation Document: Onboard hydrogen storage for light-Duty fuel Cell Vehicles. 2017. https://www. energy.gov/eere/fuelcells/.
Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Hydrogen storage in platinum loaded single-walled carbon nanotubes Anshu Sharma Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
highlights A simple and effective method to load Pt on SWNT is presented. Morphological changes in SWNT after loading of Pt is discussed. Investigation on thermal stability of SWNT with and without Pt loading. H2 storage capacities of SWNT and SWNT/Pt at 77 K and RT are discussed.
article info
abstract
Article history:
To study the hydrogen storage capacity, platinum (Pt) nanoparticles were deposited on
Received 21 March 2019
single-walled carbon nanotubes (SWNT) using hexachloroplatinic acid (H2PtCl6$6H2O) as a
Received in revised form
precursor. To verify Pt deposition on the surface of the SWNT, a Transmission Electron
30 April 2019
Microscope (TEM) was used to obtain surface morphology. The TEM images show that Pt
Accepted 4 September 2019
nanoparticles were homogeneously distributed on the surface of SWNT. Commercial
Available online xxx
SWNT were also used to compare the results. Thermal Gravimetric Analysis at heating rate of 5 C/min is measured for pure SWNT and Pt loaded SWNT. Before hydrogen storage
Keywords:
measurements these samples were reduced in 10% of H2 in Ar, flowing at 900 C in a
Single-walled carbon nanotubes
tubular furnace for 1 hour. Hydrogen storage capacity of these SWNT was investigated
Platinum nanoparticles
under 25 bar pressure and room temperature as well as liquid nitrogen temperature.
Hydrogen storage
© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Physisorption
Introduction Hydrogen has the highest energy density 120 MJ/kg over all possible fuels and this value is three times higher than gasoline. It is most abundant and an environmentally friendly energy carrier as water is its end combustion product. Regardless of all advantages, its low volumetric density (0.0899 kg/m3) at ambient conditions make it commercially limited [1,2]. Therefore hydrogen storage in a squeezed, reasonable and safer way is major technical barrier which prevents its widespread implementation as a substitute
energy carrier [3e5]. For hydrogen storage several methods including high-pressure hydrogen, liquid hydrogen, physisorption and chemisorption have been proposed. Hydrogen storage in the form of metal hydrides, compressed gas or hydrogen liquefaction possesses unadorned disadvantages [6e10]. These downsides have induced new storage conceptions as physical adsorption of hydrogen on nanomaterials. Porous materials such as metal organic frameworks has become the interest of scientific community as they shows a lot of advantages over above mentioned methods due to their fast adsorption/desorption kinetics [11e15]. Particularly
E-mail address: [email protected]. https://doi.org/10.1016/j.ijhydene.2019.09.025 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
2
international journal of hydrogen energy xxx (xxxx) xxx
unique carbon materials, such as carbon nanotubes (CNT), has considered as an auspicious contender for gas adsorption. Carbon is among the very few materials which are light and solid at room temperature (RT). CNT has many advantages like low-cost availability, heat resistance, reversibility, large thermal and chemical stability. In bundles of CNT different adsorption sites are possible for hydrogen such as interstitial networks between the single-walled carbon nanotubes (SWNT) in a bundle, pore of the SWNT and on the external surface of the tube wall or in the grooves formed at the connection between adjacent tubes [16]. Physisorption which is responsible for the hydrogen adsorption in CNT is based on the vander Waals forces between adsorbate and adsorbent. Low hydrogen storage capacities of nanomaterials at ambient conditions [17,18] indicates that at RT interaction due to vander Waals forces is as small as gas molecules have thermal energy on surface of the adsorbent. Therefore reduction in the temperature of the system induces the interaction between adsorbent and gas molecule. Physisorption is considered as a very capable method for hydrogen storage as it is based on the vander Waals forces between adsorbent and adsorbate due to which it shows fast kinetics [19,20]. To increase the hydrogen storage capacities numerous methods such as metal doping and ligand exchange have been reported. It is reported that metal precursor loaded on CNT surface exhibit an upgraded catalytic activity. A robust interaction between nanomaterial and metal precursor is essential for preparation of highly dispersed and stable catalyst. Before loading of metal catalyst particle on the surface of CNT its pretreatments such as acid functionalization introduces active sites on its surface. These pretreatments are also helpful to remove fullerene-like caps or the metal clusters at the ends of the tubes without destroying the nanotubes which allow easy access of the hydrogen to the tube interior. Properties of the functional groups, their dispersion and concentration also impact the dispersion of noble metals. Several experimental methods are introduced in CNTs loaded with metal nanoparticles which include Fe, Co, Mg, Ag, Pt, Li and Pd [21e25]. In this paper, for dissociation of hydrogen molecules and its subsequent adsorption with the possibility of Pt as a catalyst loaded on SWNT at 77 K and RT has been studied.
oil bath at 80 C for 18 h using constant stirring. Then, this acid treated product was cooled up to RT, filtered and washed with deionized water till the remained mixture grasped pH 7 then this filtrate was dried for 2 h at 100 C in an air oven. This acid treated SWNT powder used for further step. Then loading of Pt nanoparticles on the surface of SWNT were performed using a simple and efficient chemical root method. In this procedure, H2PtCl6 (10 mL) were added to the ethylene glycol (20 mL) under constant stirring to ensure the complete solubility of H2PtCl6 then acid treated SWNT (400 mg) were dispersed in to the above solution and ultrasonication was performed about 30 min. Further, this reaction mixture was stirred in an oil bath for 4 h at 120 C. Then, this mixture was filtered and washed with deionized water till filtrate reached pH7 and extracted by centrifugation using at 4000 rpm. This prepared soot was then dried in an air oven for 12 h at 80 C. In this way loading of Pt nanoparticles on the surface of SWNT was achieved [26].
Characterization techniques Transmission Electron Miicroscope (TEM) was used to investigate the morphology, size and shape of the samples. A high resolution TEM (JEOL JEM-2010F) at 200 kV was used to record the TEM images. A carbon-coated copper grid with 300 meshes was used to prepare a sample. Thermal Gravimetric Analysis (TGA) was carried out in a thermogravimetric analyzer Hitachi DSC7020. Measurements were performed in an alumina pans with heating rate of 5 C/min in air atmosphere. The final mass of the sample ranged from 5 to 12 mg. Hydrogen adsorption measurements are performed using an automated Sie-vert’s type apparatus (Setaram-HyEnergy PCT-Pro-2000) equipped with a microdoser from HyEnergy. To control the temperature, the sample was submerged in a thermal bath with liquid nitrogen (77 K) or water (300 K). The amounts of used sample are approximately 100 mg and 150 mg for SWNT and SWNT/Pt respectively.
Results and discussion TEM
Experimental details Chemicals Chloroplatinic Acid 8 wt% in water (Sigma Aldrich, Germany) and large surface area SWNT having length 5e35 mm, diameter ~1e2 nm with purity >95% (US Research Nanomaterials Inc., TX, USA) were used in this experiment. Chemical reagents such as carboxylic acid, nitric acid, ethanol etc were of commercial grade and were used as purchased.
Synthesis of SWNT/Pt nanocomposites First of all, as purchased SWNT was functionalized using carboxylic acid. In this process as purchased SWNT (500 mg) was dispersed in 25 ml of concentrated HNO3 and refluxed in
TEM measurements were carried out to measure the location, distribution and particle size of Pt nanoparticles. The as prepared SWNT/Pt nanocomposites were investigated by TEM. Fig. 1 shows the TEM image contrast of pure SWNT and SWNT/Pt composites i.e. after loading of Pt nanoparticles on SWNT. TEM images indicate that the Pt nanoparticles which are dispersed on the surface of the SWNT having an average size of 20e30 nm and do not agglomerate with each other to form a large cluster. TEM images also implies that Pt nanoparticles loaded directly on surface defect sites and pores and no single Pt nanoparticle is resolved in the TEM images which evident the strong bonding between Pt atoms and carbon atoms at the defects. Therefore above presented TEM images shows the efficiency of a simple method to load Pt nanoparticles on the surfaces of SWNT.
Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
3
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 1 e TEM images of (a) SWNT (b) SWNT/Pt. It is cleared from Fig. 2 that as purchased SWNT and Pt loaded SWNT are considerably less stable at high temperature approximate 800 C and 600 C respectively. Here TGA measurements were performed to characterize the stability of SWNT and SWNT/Pt nanocomposite toward hightemperature.
(a) SWNT (b) SWNT/Pt
100
95
Weight (%)
(a) 90
Hydrogen adsorption 85
80
(b) 75 0
200
400
600
800
1000
Temperature (oC)
Fig. 2 e TGA of (a) SWNT and (b) SWNT/Pt.
TGA Determination of the amount of loaded Pt nanoparticles catalyst on the surfaces of SWNT was analyzed by TGA in an air atmosphere. It is a simple analytical technique that is frequently used to determine the decomposition temperature of the CNT.
0.60
(a)SWNT at 77K
Adsorption Desorption
0.55
Figs. 3 and 4 shows the hydrogen adsorption/desorption analyses of as purchased SWNT and SWNT/Pt at 77 K and RT respectively. The measured isotherm shows no saturation at RT. At low temperature a slight increase in adsorption can be observed. At low temperature no saturation of the pressure isotherms can be determined at pressure up to 25 bar. The adsorption reached 0.55e0.60 wt% at 77 K and 25 bar in the case of pure SWNT but as Pt is loaded in SWNT adsorption isotherm reached 0.65e0.70 wt% at 77 K and 25 bar which is greater than pure SWNT. This indicates that the high pressure adsorption is confirmed in SWNT but very high values could not be reproduced. The adsorption occurs due to attractive potential of the pore walls [27,28]. After loading Pt catalyst hydrogen could be physisorbed on SWNT exposed surfaces. Experimental results shown here indicated that at cryogenic temperatures the hydrogen adsorption in the interstitial sites of SWNT bundles
0.020
(b)SWNT at RT
Adsorption Desorption
0.45
Absolute H2 uptake (wt%)
Absolute H2 uptake (wt%)
0.50
0.015
0.40 0.35
0.010
0.30 0.25
0.005
0.20 0.15 0.10
0.000
0.05 0.00 0
5
10
15
Pressure (bar)
20
25
-0.005
0
10
20
30
Pressure (bar)
Fig. 3 e H2 adsorption/desorption isotherms of (a) SWNT at 77 K (b) SWNT at RT. Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
4
international journal of hydrogen energy xxx (xxxx) xxx
0.70
Adsorption Desorption
0.65 0.60
(a)SWNT/Pt at 77K
0.020
(b)SWNT/Pt at RT
Adsorption Desorption
0.018
Absolute H2uptake (wt%)
AbsoluteH2 uptake (wt%)
0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 -0.05
0.016 0.014 0.012 0.010 0.008 0.006 0.004
0
5
10
Pressure (bar)
15
20
25
0
10
Pressure (bar)
20
30
Fig. 4 e H2 adsorption/desorption isotherms of (a) SWNT/Pt at 77 K (b) SWNT/Pt at RT.
possessing a very wide tube diameter and extreme separation could not sufficient to achieve the gravimetric hydrogen storage for DOE target [29].
Conclusion A facile method to load Pt catalysis on SWNT is devised successfully. This study highlights a very simple but efficient synthesis approach for high loading of Pt on SWNT with uniform dispersion. Through the acid treatment large quantities of homogeneously distributed active sites can be generated for anchoring Pt nanoparticles. Physical characterizations revealed that Pt nanoparticles were successfully deposited on the surface of SWNT with a very good density. CNT samples, including SWNT and Pt loaded SWNT were used for hydrogen storage purpose by a gravimetric measurement method. Hydrogen storage capacity of these samples were found less than 1 wt% in both of the cases having conditions of hydrogen gas pressure 25 bar at 77 K and 25 bar at RT. These results suggest that high pressure hydrogen storage is confirmed in SWNT but very high values could not be reproduced. Therefore it is concluded that hydrogen storage capacity of SWNT is far below the DOE targets and it is unfeasible for on-board hydrogen uptake systems. In the other side, for significantly improving their hydrogen storage capacity and kinetics an effective additive can be used in SWNT.
Acknowledgements The author gratefully acknowledges the financial support of the Department of Science and Technology, Ministry of Science and Technology, Govt. of India under women scientists scheme (WOS-A) grant SR/WOS-A/PS-62/2013. Author is highly thankful to Max Planck Institute for the Structure and Dynamics of Matter, Germany for providing experimental facilities for sample preparation and Max Planck Institute for Intelligent System, Stuttgart, Germany for providing hydrogen storage measurements under Max Planck-India mobility grant supported by Max Planck Society, Germany and Indo-German Science and Technology Centre, Department of Science and Technology, Ministry of Science and Technology, Govt. of India.
references
[1] Dillon AC, Heben MJ. Hydrogen storage using carbon adsorbents: past, present and future. Appl Phys A 2001;72:133e42. [2] Wang L, Yang RT. New sorbents for hydrogen storage by hydrogen spillover-A review. Energy Environ Sci 2008;1:268e79. [3] Yurum Y, Taralp A, Veziroglu TN. Storage of hydrogen in nanostructured carbon materials. Int J Hydrogen Energy 2009;34(9):3784e98. [4] De La Casa-Lillo MA, Lamari-Darkrim F, Cazorla Amoros D, Linares Solano A. Hydrogen storage in activated carbons and activated carbon fibers. J Phys Chem B 2002;106:10930e4. [5] Midilli A, Ay M, Dincer I, Rosen MA. On hydrogen and hydrogen energy strategies: I: current status and needs. Renew Sustain Energy Rev 2005;9(3):255e71. [6] Broom DP, Webb CJ, Hurst KE, Parilla PA, Gennett T, Brown CM, Zacharia R, Tylianakis E, Klontzas E, Froudakis GE, Steriotis TA, Trikalitis PN, Anton DL, Hardy B, Tamburello D, Corgnale C, Van Hassel BA, Cossement D, Chahine R, Hirscher M. Outlook and challenges for hydrogen storage in nanoporous materials. Appl Phys A 2016;122:151 (1e21). [7] Mehrabi M, Parvin P, Reyhani A, Mortazavi SZ. Hydrogen storage in multi-walled carbon nanotubes decorated with palladium nanoparticles using laser ablation/chemical reduction methods. Mater Res Express 2017;4:095030. [8] Tellez Juarez MC, Fierro V, Zhao W, Fernandez Huerta N, Izquierdo MT, Reguera E, Celzard A. Hydrogen storage in activated carbons produced from coals of different ranks: effect of oxygen content. Int J Hydrogen Energy 2014;39(10). 4996e02. [9] Joo SH, Choi SJ, Oh I, Kwak J, Liu Z, Terasaki O, Ryoo R. Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles. Nature 2001;412:169e72. [10] Zhao W, Fierro V, Fernandez Huerta N, Izquierdo MT, Celzard A. Hydrogen uptake of high surface area-activated carbons doped with nitrogen. Int J Hydrogen Energy 2013;38(25):10453e60. [11] Gogotsi Y, Portet C, Osswald S, Simmons JM, Yildirim T, Laudisio G, Fischer JE. Importance of pore size in highpressure hydrogen storage by porous carbons. Int J Hydrogen Energy 2009;34(15):6314e9. [12] Yang SJ, Im JH, Nishihara H, Jung H, Lee K, Kyotani T, Park CR. General relationship between hydrogen
Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025
international journal of hydrogen energy xxx (xxxx) xxx
[13] [14]
[15]
[16] [17]
[18]
[19] [20]
[21]
adsorption capacities at 77 and 298 K and pore characteristics of the porous adsorbents. J Phys Chem C 2012;116(19):10529e40. Broom DP, Hirscher M. Irreproducibility in hydrogen storage material research. Energy Environ Sci 2016;9(11):3368e80. Liu X, Zhang C, Geng Z, Cai M. High-pressure hydrogen storage and optimizing fabrication of corncob-derived activated carbon. Microporous Mesoporous Mater 2014;194:60e5. Oh H, Gennett T, Atanassov P, Kurttepeli M, Bals S, Hurst KE, Hirscher M. Hydrogen adsorption properties of platinum decorated hierarchically structured templated carbons. Microporous Mesoporous Mater 2013;177:66e74. Hirscher M, Becher M. Hydrogen storage in carbon nanotubes. J Nanosci Nanotechnol 2003;3:3e17. Liu Z, Xue Q, Ling C, Yan Z, Zheng J. Hydrogen storage and release by bending carbon nanotubes. Comput Mater Sci 2013;68:121e6. Nasruddin N, Kosasih EA, Kurniawan B, Supriyadi S, Zulkarnain IA. Optimization of hydrogen storage capacity by physical adsorption on open-ended single-walled carbon nanotube as diameter function. Int J Technol 2016;2:264e73. Bhatia SK, Myers AL. Optimum conditions for adsorptive storage. Langmuir 2006;22(4):1688e700. Barghi SH, Tsotsis TT, Sahimi M. Chemisorption, physisorption and hysteresis during hydrogen storage in carbon nanotubes. Int J Hydrogen Energy 2014;39:1390e7. Li J, Zhang H, Yang G. Ultrahigh-capacity molecular hydrogen storage of a lithium-decorated boron monolayer. J Phys Chem C 2015;119:19681e8.
5
[22] Li Y, Yang RT. Hydrogen storage on platinum nanoparticles doped on superactivated carbon. J Phys Chem C 2007;111:11086e94. [23] Adjizian JJ, Marco PD, Martinez IS, Mel AAE, Snyders R, Gengler RYN, Rudolf P, Ke X, Tendeloo GV, Bittencourt C, Ewels CP. Platinum and palladium on carbon nanotubes: experimental and theoretical studies. Chem Phys Lett 2013;571:44e8. [24] Sevilla M, Fuertes AB, Mokaya R. Preparation and hydrogen storage capacity of highly porous activated carbon materials derived from polythiophene. Int J Hydrogen Energy 2011;36(24):15658e63. [25] Georgakis M, Stavropoulos G, Sakellaropoulos GP. Molecular dynamics study of hydrogen adsorption in carbonaceous microporous materials and the effect of oxygen functional groups. Int J Hydrogen Energy 2007;32(12):1999e2004. [26] Sharma A, Andreas R, Nehra SP. Synthesis of SWNT/Pt nanocomposites for their effective role in hydrogen storage applications. AIP Conf Proc 2018;1953:030148. [27] Govind Sethia G, Sayari A. Activated carbon with optimum pore size distribution for hydrogen storage. Carbon 2016;99:289e94. [28] Broom DP, Webb CJ. Pitfalls in the characterization of the hydrogen sorption properties of materials. Int J Hydrogen Energy 2017;42(49):29320e43. [29] DoE, Target Explanation Document: Onboard hydrogen storage for light-Duty fuel Cell Vehicles. 2017. https://www. energy.gov/eere/fuelcells/.
Please cite this article as: Sharma A, Hydrogen storage in platinum loaded single-walled carbon nanotubes, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.025