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Storage of hydrogen is a critical challenge for various applications due to its high reactivity and the necessity for high capacity- high pressure storage medium which is not favourable [1]. The potential solution is adsorption of hydrogen onto a solid support which would allow storage at relatively low pressures and high temperatures. In Multi-Walled Carbon Nanotubes (MWNTs), the storage of hydrogen can be done only on the outer wall and inner hollow of the carbon structure whereas the volume between the concentric layers is not accessible [2]. Single-Walled Carbon Nanotubes (SWNT) provide efficient use of large internal volume and the entire surface. The adsorption capacity of highly porous SWNT is immense because of their uniform and dense microporous structures, low macro-porosity and high thermal conductivity [3].
The maximum storage can be attained by manipulating the diameter and length of SWNT[7]. Arc discharge Carbon Nanotubes (CNT) have different primary carbon forms with entangled network of fibres and clusters of different sizes. Arc CNT are planned for hydrogen storage, a more compact form of the material is essential to increase the volumetric density of hydrogen [4].
Larger quantities of high purity SWNTs, such as those produced using the HiPCO® method have smaller diameter ranging from 0.6 -1 nm exhibiting a microporous structure around 0.5- 0.9nm[3]. These micropores have the advantage of adsorption in the interstitial space at the interior of the bundles between individual tubes and adsorption in the outer trenches at the surface of the bundles [3].
The purified HiPCO® SWNTs had established more storage capacity compared to the As-prepared SWNTs [5]. The smaller diameter NoPo HiPCO® Single Wall Carbon Nanotubes can be used to increase the storage rate of hydrogen by tuning the microporous diameter and low pressure[3]. NoPo has the expertise in making purified HiPCO® SWNTs which enables functionalization of SWNTs results in small diameter SWCNTs.
References:
[1] Eberle, Ulrich, Michael Felderhoff, and Ferdi Schueth. “Chemical and physical solutions for hydrogen storage.” Angewandte Chemie International Edition 48.36 (2009): 6608-6630.
[2] Ning, G. Q., et al. “Hydrogen storage in multi-wall carbon nanotubes using samples up to 85 g.” Applied Physics A 78.7 (2004): 955-959.
[3] Du, Wei-Fang, et al. “Investigation of the pore structure of as-prepared and purified HiPco single-walled carbon nanotubes by N2/Ar adsorption implication for H2 storage.” Nano letters 2.4 (2002): 343-346.
[4] Anson, A., Callejas, M. A., Benito, A. M., Maser, W. K., Izquierdo, M. T., Rubio, B., & Martınez, M. T. (2004). Hydrogen adsorption studies on single wall carbon nanotubes. Carbon, 42(7), 1243-1248.
[5] Darkrim, F. Lamari, P. Malbrunot, and G. P. Tartaglia. “Review of hydrogen storage by adsorption in carbon nanotubes.” International Journal of Hydrogen Energy 27.2 (2002): 193-202.
[6] Rajaura, Rajveer Singh, et al. “Structural and surface modification of carbon nanotubes for enhanced hydrogen storage density.” Nano-Structures & Nano-Objects 14 (2018): 57-65.
[7] Ma, Ychen, et al. “Hydrogen storage capacity in single-walled carbon nanotubes.” Physical Review B 65.15 (2002): 15u5430.