Carbon nanotubes are microscopic tubes of carbon, two nanometers (billionths of a meter) across, that store hydrogen in microscopic pores on the tubes and within the tube structures. Similar to metal hydrides in their mechanism for storing and releasing hydrogen, the advantage of carbon nanotubes is the amount of hydrogen they are able to store. Carbon nanotubes are capable of storing anywhere from 4.2% - to 65% of their own weight in hydrogen. A novel mechanism of hydrogen storage in carbon nanotubes is proposed by using the density functional calculations. Several key intermediate states are identified for hydrogen adsorption. Up to the coverage of 1.0, hydrogen atoms chemisorb on the nanotube wall with either an arch type or a zigzag type. Then, hydrogen can be further stored inside the nanotubes at higher coverage as a molecular form. Hydrogen atoms can be inserted into the nanotubes through the tube wall via flip-in and/or kick-in mechanism with activation barriers of 1.5 and 2.0 eV, respectively. In the hydrogen extraction process, hydrogen molecules inside a nanotube firstly dissociates onto the inner wall with an activation barrier of 1.6 eV. Secondly, hydrogen atoms at the interior of the tube wall are further extracted to the outer wall by the flip-out mechanism with an activation barrier of 2.0 eV.
Our studies of carbon nano-material adsorptive properties for hydrogen, containing ~ 70 w/w % of SWNTs, showed that the materials were capable of absorbing ~ 3.5 w/w % of hydrogen at 100 atm at room temperature and evolving hydrogen at pressures drop down to 1 atm. Analysis of scientific publications shows that the experimental data are often contradictory, however, a comparative analysis of the systems for hydrogen storage on the whole shows that the parameters of carbon nano-materials are close to those required for motor transport. The reason of the parameter discrepancy is the lack of reliable methods for carbon nano-materials certification, namely, the content of SWNT and MWNT, the content of open tubes and the distribution in diameter. Additionally, residual catalysts affect hydrogen sorption.
Single-walled carbon nanotubes (SWNT) hold great promises as hydrogen storage medium. Their unique architecture makes them the best carbon-based adsorbent for hydrogen. It has been predicted theoretically that gravimetric density of up to 16 weight percent of H2 and volumetric density of 160 kg/m3 of H2 can be stored in (10,10) SWNT. This value exceeds greatly the US Department of Energy's energy density target of 6.5 weight percent and 62 kg/m3 for an economically viable vehicular hydrogen storage medium. This value has never been obtained experimentally in a reproducible way, creating much controversy in the field. This is because of the lack of controls in the synthesis of SWNT, the lack of understanding of the effects of chemical modifications through the purification processes, and the lack of understanding of how molecular hydrogen interacts with SWNT.
ENER1 has the necessary experience and expertise to carry out studies of electrochemical intercalation of Li and other alkali metals into carbon nano-materials. According to predictions, carbon nanotubes intercalated by Li can demonstrate high electrochemical capacity (up to 640 mAh/g) in the first cycles, though capacity can decrease in cycling.
==Carbon nanotubes in their single-walled form are typically around 1.3 nm in diameter and are on the order of 100um in length. They occur in three different structural forms, with different diameters, the proportions of which are difficult to control in synthesis. The three principal production methods are laser vaporisation of a Ni/Co-doped graphite target, DC arc using a Ni/Y-doped graphite anode, and vapour growth using Fe, Co and Ni catalyst particles with a hydrocarbon feedstock at 1000 degC. Of these methods, the DC arc has better scalability. The storage potential of nanotubes is in the range of 2 - 14 hydrogen weight percent, with claims of up to 72 weight percent made for graphitic nanofibres. Advantages of carbon nanostructures as storage media include their low mass density, chemical stability (up to 900 degC in an inert atmosphere)and fast sorption kinetics compared to metal hydrides, owing to the hydrogen uptake being a surface rather than a bulk process. At present they suffer from the disadvantages of being very expensive to produce in practically useful quantities, difficulties in purification of raw nanofibre material, and the need for low temperatures or high pressures to achieve high levels of storage.
DERA's info:
Store up to 10 wt % H 2
Require either:
high pressure (>100 bar)
low temperature (< -100 o C) Different forms MWNT SWNT capped uncapped 1-10 nm diameter Links:http://www.eren.doe.gov/hydrogen/pdfs/30535an.pdfhttp://www.foresight.org/Conferences/MNT9/Abstracts/Simard/ http://www.nanotube.org/abs/LeeSM.htmlhttp://www.personal.psu.edu/faculty/b/k/bkp5/hydrogen.html http://www.ener1.com/b_storage.shtml
Carbon nanofibers
DERA's info:
Developed by Northeastern University
Consist of stacked graphite plates
Thin fibres of 5-100 nm diameter and 5-100mm length
Spacing between planes (0.34 nm) perfect for H2 (H2 diameter of 0.29 nm)
Potentially store over 50 wt % H 2 (9300 Wh/kg)
Room temperature storage
High pressure required
Our studies of carbon nano-material adsorptive properties for hydrogen, containing ~ 70 w/w % of SWNTs, showed that the materials were capable of absorbing ~ 3.5 w/w % of hydrogen at 100 atm at room temperature and evolving hydrogen at pressures drop down to 1 atm. Analysis of scientific publications shows that the experimental data are often contradictory, however, a comparative analysis of the systems for hydrogen storage on the whole shows that the parameters of carbon nano-materials are close to those required for motor transport. The reason of the parameter discrepancy is the lack of reliable methods for carbon nano-materials certification, namely, the content of SWNT and MWNT, the content of open tubes and the distribution in diameter. Additionally, residual catalysts affect hydrogen sorption.
Single-walled carbon nanotubes (SWNT) hold great promises as hydrogen storage medium. Their unique architecture makes them the best carbon-based adsorbent for hydrogen. It has been predicted theoretically that gravimetric density of up to 16 weight percent of H2 and volumetric density of 160 kg/m3 of H2 can be stored in (10,10) SWNT. This value exceeds greatly the US Department of Energy's energy density target of 6.5 weight percent and 62 kg/m3 for an economically viable vehicular hydrogen storage medium. This value has never been obtained experimentally in a reproducible way, creating much controversy in the field. This is because of the lack of controls in the synthesis of SWNT, the lack of understanding of the effects of chemical modifications through the purification processes, and the lack of understanding of how molecular hydrogen interacts with SWNT.
ENER1 has the necessary experience and expertise to carry out studies of electrochemical intercalation of Li and other alkali metals into carbon nano-materials. According to predictions, carbon nanotubes intercalated by Li can demonstrate high electrochemical capacity (up to 640 mAh/g) in the first cycles, though capacity can decrease in cycling.
==Carbon nanotubes in their single-walled form are typically around 1.3 nm in diameter and are on the order of 100um in length. They occur in three different structural forms, with different diameters, the proportions of which are difficult to control in synthesis. The three principal production methods are laser vaporisation of a Ni/Co-doped graphite target, DC arc using a Ni/Y-doped graphite anode, and vapour growth using Fe, Co and Ni catalyst particles with a hydrocarbon feedstock at 1000 degC. Of these methods, the DC arc has better scalability. The storage potential of nanotubes is in the range of 2 - 14 hydrogen weight percent, with claims of up to 72 weight percent made for graphitic nanofibres. Advantages of carbon nanostructures as storage media include their low mass density, chemical stability (up to 900 degC in an inert atmosphere)and fast sorption kinetics compared to metal hydrides, owing to the hydrogen uptake being a surface rather than a bulk process. At present they suffer from the disadvantages of being very expensive to produce in practically useful quantities, difficulties in purification of raw nanofibre material, and the need for low temperatures or high pressures to achieve high levels of storage.
DERA's info:
Store up to 10 wt % H 2
Require either:
high pressure (>100 bar)
low temperature (< -100 o C) Different forms MWNT SWNT capped uncapped 1-10 nm diameter Links:http://www.eren.doe.gov/hydrogen/pdfs/30535an.pdfhttp://www.foresight.org/Conferences/MNT9/Abstracts/Simard/ http://www.nanotube.org/abs/LeeSM.htmlhttp://www.personal.psu.edu/faculty/b/k/bkp5/hydrogen.html http://www.ener1.com/b_storage.shtml
Carbon nanofibers
DERA's info:
Developed by Northeastern University
Consist of stacked graphite plates
Thin fibres of 5-100 nm diameter and 5-100mm length
Spacing between planes (0.34 nm) perfect for H2 (H2 diameter of 0.29 nm)
Potentially store over 50 wt % H 2 (9300 Wh/kg)
Room temperature storage
High pressure required
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