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Title: Tailoring of Single Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports

Abstract

We report the post-processing chemical treatments of single walled carbon nanohorns (SWNHs) as a medium with tunable porosity to optimize hydrogen adsorption. Laser synthesized SWNHs are oxidized in air to achieve surface areas up to 1900 m2/g. Chemistry methods are described for the decoration of SWNHs with 1-3 nm Pt nanoparticles to probe spillover and metal-assisted hydrogen storage mechanisms. Hydrogen storage of opened SWNHs is 2.6 wt% at 77K, which is 3 times as that of as-prepared SWNHs.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [2];  [2];  [3];  [4];  [3]
  1. ORNL
  2. Indiana University Cyclotron Facility, Bloomington, IN
  3. National Institute of Standards and Technology (NIST)
  4. California Institute of Technology, Pasadena
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Center for Nanophase Materials Sciences (CNMS)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC)
OSTI Identifier:
1158730
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: Carbon 2007 Conference, Seatlle, WA, USA, 20070715, 20070720
Country of Publication:
United States
Language:
English
Subject:
Single Walled; Nanohorns; Hydrogen Storage

Citation Formats

Hu, Hui, Zhao, Bin, Puretzky, Alexander A, Rouleau, Christopher M, Styers-Barnett, David J, Geohegan, David B, Brown, Craig M., Liu, Yun, Zhou, Wei, Kabbour, Houria, and Neumann, Dan. Tailoring of Single Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports. United States: N. p., 2007. Web.
Hu, Hui, Zhao, Bin, Puretzky, Alexander A, Rouleau, Christopher M, Styers-Barnett, David J, Geohegan, David B, Brown, Craig M., Liu, Yun, Zhou, Wei, Kabbour, Houria, & Neumann, Dan. Tailoring of Single Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports. United States.
Hu, Hui, Zhao, Bin, Puretzky, Alexander A, Rouleau, Christopher M, Styers-Barnett, David J, Geohegan, David B, Brown, Craig M., Liu, Yun, Zhou, Wei, Kabbour, Houria, and Neumann, Dan. Mon . "Tailoring of Single Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports". United States. doi:.
@article{osti_1158730,
title = {Tailoring of Single Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports},
author = {Hu, Hui and Zhao, Bin and Puretzky, Alexander A and Rouleau, Christopher M and Styers-Barnett, David J and Geohegan, David B and Brown, Craig M. and Liu, Yun and Zhou, Wei and Kabbour, Houria and Neumann, Dan},
abstractNote = {We report the post-processing chemical treatments of single walled carbon nanohorns (SWNHs) as a medium with tunable porosity to optimize hydrogen adsorption. Laser synthesized SWNHs are oxidized in air to achieve surface areas up to 1900 m2/g. Chemistry methods are described for the decoration of SWNHs with 1-3 nm Pt nanoparticles to probe spillover and metal-assisted hydrogen storage mechanisms. Hydrogen storage of opened SWNHs is 2.6 wt% at 77K, which is 3 times as that of as-prepared SWNHs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • The objective of the project was to exploit the unique morphology, tunable porosity and excellent metal supportability of single-walled carbon nanohorns (SWNHs) to optimize hydrogen uptake and binding energy through an understanding of metal-carbon interactions and nanoscale confinement. SWNHs provided a unique material to understand these effects because they are carbon nanomaterials which are synthesized from the 'bottom-up' with well-defined, sub-nm pores and consist of single-layer graphene, rolled up into closed, conical, horn-shaped units which form ball-shaped aggregates of {approx}100-nm diameter. SWNHs were synthesized without metal catalysts by the high-temperature vaporization of solid carbon, so they can be used tomore » explore metal-free hydrogen storage. However, SWNHs can also be decorated with metal nanoparticles or coatings in post-processing treatments to understand how metals augment hydrogen storage. The project first explored how the synthesis and processing of SWNHs could be modified to tailor pore sizes to optimal size ranges. Nanohorns were rapidly synthesized at 20g/hr rates by high-power laser vaporization enabling studies such as neutron scattering with gram quantities. Diagnostics of the synthesis process including high-speed videography, fast pyrometry of the graphite target, and differential mobility analysis monitoring of particle size distributions were applied in this project to provide in situ process control of SWNH morphology, and to understand the conditions for different pore sizes. We conclude that the high-temperature carbon-vaporization process to synthesize SWNHs is scalable, and can be performed by electric arc or other similar techniques as economically as carbon can be vaporized. However, the laser vaporization approach was utilized in this project to permit the precise tuning of the synthesis process through adjustment of the laser pulse width and repetition rate. A result of this processing control in the project was to eliminate the large (2-3 nm) internal pores of typical SWNHs which were found not to store hydrogen effectively. Post processing treatments of the as-synthesized SWNHs focused on pore size, surface area, and metal decoration in order to understand the effects of each on measured hydrogen uptake. Wet chemistry and gas-phase oxidation treatments were developed throughout the life of the project to adjust the interstitial and slit pore sizes of the as-produced SWNHs, and increase the surface area to a maximum value of 2200 m2/g. In addition, wet chemistry approaches were used to develop methods to decorate the nanohorns with small Pt and Pd nanoparticles for metal-assisted hydrogen storage. Finally, oxygen-free decoration of SWNHs with alkaline earth metals (Ca) was developed using pulsed laser deposition and vacuum evaporation in order to produce surface coatings with high static electric fields sufficient to polarize and bind dihydrogen. Decoration of SWNHs with Pt and Pd nanoparticles resulted in enhanced binding energy (NREL, 36 kJ/mol), as well as enhancement in the room temperature uptake of 0.6 wt.% (for undecorated, oxidized, pure-C SWNHs at 20 bar), to 1.6 wt% for Pt- and Pd-decorated SWNHs at 100 bar, comparable to MOF-177 materials. NIST neutron scattering on gram quantity Pt- and Pd-decorated SWNHs showed clear evidence for 'spillover' type losses of molecular hydrogen and determined the onset temperature for this effect to be between 150K < T < 298K.High (2142 m2/g) surface area SWNH materials with variable pore sizes and metal-decorated SWNHs were demonstrated with metals (Pt, Pd) resulting in increased excess storage (3.5 wt. % at 77K). Compression results in bulk SWNH samples with density 1.03 g/cm3, and 30 g/L volumetric capacity. In summary, SWNHs were found to be unique carbon nanomaterials which can be produced continuously at high rates from vaporization of pure carbon. Their inherent pore structure exhibits significant room temperature hydrogen storage in sub-nm pores, and their morphology serves as an excellent metal catalyst support for small (2-3 nm nanoparticles). Pt- and Pd-nanoparticle-decorated SWNHs exhibit clear evidence for metal-assisted hydrogen storage which is activated at T>150 K, permitting additional room-temperature storage up to 1.8 wt.% at 100 bar. One of the key results of the project were theoretical predictions for doped, decorated, and filled nanostructures with distributed charge to maintain high static electric fields sufficient to polarize and bind hydrogen. This concept indicates a promising new direction for hydrogen storage materials.« less
  • The catalytic dissociation of hydrogen molecules by metal nanoparticles and spillover of atomic hydrogen onto various supports is a well-established phenomenon in catalysis. However, the mechanisms by which metal catalyst nanoparticles can assist in enhanced hydrogen storage on high-surface area supports are still under debate. Experimental measurements of metal-assisted hydrogen storage have been hampered by inaccurate estimation of atomically stored hydrogen deduced from comparative measurements between metal-decorated and undecorated samples. Here we report a temperature cycling technique combined with inelastic neutron scattering (INS) measurements of quantum rotational transitions of molecular H2 to more accurately quantify adsorbed hydrogen aided by catalyticmore » particles using single samples. Temperature cycling measurements on single-wall carbon nanohorns (SWCNHs) decorated with 2-3 nm Pt nanoparticles showed 0.17 % mass fraction of metal-assisted hydrogen storage (at 0.5 MPa) at room temperature. Temperature cycling of Pt-decorated SWCNHs using a Sievert s apparatus also indicated metal-assisted hydrogen adsorption of 0.08 % mass fraction at 5 MPa at room temperature. No additional metal-assisted hydrogen storage was observed in SWCNH samples without Pt nanoparticles cycled to room temperature, or in Pt-SWCNHs when the temperature was cycled to less than 150K. The possible formation of C-H bonds due to spilled-over atomic hydrogen was also investigated using both INS and density functional theory calculations.« less
  • Previous studies have suggested that single-walled carbon nanotubes (SWCNTs) may pose a pulmonary hazard. We investigated the pulmonary toxicity of single-walled carbon nanohorns (SWCNHs), a relatively new carbon-based nanomaterial that is structurally similar to SWCNTs. Mice were exposed to 30 {micro}g of surfactant-suspended SWCNHs or an equal volume of vehicle control by pharyngeal aspiration and sacrificed 24 hours or 7 days post-exposure. Total and differential cell counts and cytokine analysis of bronchoalveolar lavage fluid demonstrated a mild inflammatory response which was mitigated by day 7 post-exposure. Whole lung microarray analysis demonstrated that SWCNH-exposure did not lead to robust changes inmore » gene expression. Finally, histological analysis showed no evidence of granuloma formation or fibrosis following SWCNH aspiration. These combined results suggest that SWCNH is a relatively innocuous nanomaterial when delivered to mice in vivo using aspiration as a delivery mechanism.« less
  • Previous studies have suggested that single-walled carbon nanotubes (SWCNTs) may be pose a pulmonary hazard. We investigated the pulmonary toxicity of single-walled carbon nanohorns (SWCNHs), a relatively new carbon-based nanomaterial that is structurally similar to SWCNTs. Mice were exposed to 30 g of surfactant-suspended SWCNHs by pharyngeal aspiration and sacrificed 24 hours or 7 days post exposure. Total and differential cell counts and cytokine analysis of bronchoalveolar lavage fluid demonstrated a mild inflammatory response which was mitigated by day 7 post exposure. Whole lung microarray analysis demonstrated that SWCNH-exposure did not lead to robust changes in gene expression. Finally, histologicalmore » analysis showed no evidence of granuloma formation or fibrosis following SWCNH aspiration. These combined results suggest that SWCNH is a relatively innocuous nanomaterial when delivered to mice in vivo using aspiration as a delivery mechanism.« less
  • A high-speed vibration milling (HSVM) method was applied to synthesize water dispersible single- walled carbon nanohorns (SWNHs). Highly reactive free radicals (HOOCCH2CH2 ) produced from an acyl peroxide under HSVM conditions react with hydrophobic SWNHs to produce a highly water dispersible derivative (f-SWNHs), which has been characterized in detail by spectroscopic and microscopic techniques together with thermogravimetric analysis (TGA) and dynamic light scatter- ing (DLS). The carboxylic acid functionalized, water-dispersible SWNHs material are versatile precursors that have potential applications in the biomedical area.