CONTENTS Nanotechnology Introduction to the topic History Why carbon nanotubes? Fundamentals for Hydrogen Storage i. Physisorption ii.Chemisorption Comparison table Synthesis Doping Conclusion References
NANOTECHNOLOGY Nanotechnology is the creation of useful/functional materials, devices and systems (of any useful size ) through control manipulation of matter on the 1-100nm length scale and the use of novel phenomena and properties which arise because of nanometer length scale.Nanometer One billionth of a meter (10-9 m) Hydrogen atom 0.04nm Proteins 1-20nm Chemically reactivity differs . Improved mechanical properties Increased surface area New chemical formulation
INTRODUCTIONCarbon nanotubes are extremely thin hollow cylinders made of carbon with pores thatcan store gases by the phenomena of adsorption.Various carbon nanotubesSingle walled nanotubes (SWNT) - diameter range of 0.4 to 3nm .Multi walled nanotubes (MWNT) - several sheets, arranged concentrically inincreasingly larger diameters with diameters in the range of 1.4 to 100 nm.Metal doped nanotubes - Obtained by doping of various metals to carbon nanotubes.
HISTORY After Kroto & Smalley discovered Fullerene, one of carbon allotropes (a cluster of 60 carbon atoms: C60) for the first time in 1985, Dr.Iijima, a researcher for this new material , in Japan discovered in 1991, a thin long straw-shaped carbon Nanotubes during TEM analysis of carbon clusters.
PROPERTIES A carbon atom in nanotube forms a hexagonal lattice of sp² bond with three other carbon atoms. As the inner diameters of the tubes are extremely thin down to about several nanometers, the tubes are called Nanotubes. Thermal conductivity (>3000 W/m-K), The elastic ability to extend ≈5.8% of its original length More appealing still is the disproportionately large surface area to volume that these materials possess , for this allows for a greater potential of interactions, both physical or chemical in nature
APPLICATIONS IN HYDROGEN STORAGE Depleting non- renewable source of energy prompting us to move to an energy resource which is abundantly available and which is eco- friendly as well. „Hydrogen‟ ,sought as future fuel because of high energy content than any other fuel, at least 3 times than gasoline. Advantage- clean fuel, byproduct only water. Disadvantage- low energy density by volume. So difficult to store and transport.
WHY CARBON NANOTUBES FOR H2 STORAGEAvailable techniques for hydrogen storage- As cryogenic liquid As pressurized gas As physical combination with metal hydrides/complex hydrides on board production By reform of methanol Carbon nanotubes
HYDROGEN STORAGE FUNDAMENTALSPhysisorption Based on Vander Waal‟s interaction. Stem from intermolecular forces between atoms that result from instantaneous charge distribution in atoms & molecules when they approach each other. The interaction energy, also called the London Dispersion forces Adsorption on a flat carbon surface depends on the adsorption stereometry. An average value would be 4-5 kj mol⁻1.This represents a very weak interaction .Therefore, hydrogen is desorbed with increasing temperature, and a very little hydrogen adsorption is observed on carbon at elevated temperature.
CHEMISORPTION If the π-bonding between the carbon atom were to be fully utilized, every carbon atom could be a site for chemisorptions of one hydrogen atom. Desorption results of nanotubes treated with chemisorbed hydrogen, however, can only be released at higher temperatures. Hydrogen storage in CNTs by chemical reaction, on the other hand , has largely been discounted as irreversible and thus technologically less relevant
TABLE 1.1 VARIOUS SAMPLES OF CARBON NANOTUBES AND THEIR HYDROGEN STORAGE CAPACITY ,Sample % Purity H₂ (wt%) T(K) P(MPa) Ref.SWNTs Assumed 100 5-10 133 0.04 (A.C. Dillon et al., 1997)SWNTs 50 4.2 300 10.1 (C. Liu et al,1999)SWNTs High 8.25 80 7 (Y. Ye et al, 1999)SWNTs Purified 1.2 Ambient 4.8 (Smith Jr, Bittner,Shi, Jhonson, & Bockrath, 2003)SWNTs 90 vol% 0.63 298 - (Ritschel et al., 2002)SWNTs Purified 6 77 0.2 (Pradhan et al., 2002)SWNTs Unpurified 0.93 295 0.1 (Nishimaya et al., 2002)SWNTs Unpurified 0.37 77 0.1 (Nishimaya et al., 2002)MWNTs Purified 0.25 ~300-700 Ambient (Wu et al., 2000)MWNTs Unpurified 0.5 298 - (Ritschel et al., 2002)MWNTs High 5-7 300 1.0 (Y. Chen et al., 2001)MWNTs High, acid treated 13.8 300 1.0 (Y. Chen et al., 2001)MWNTs High 0.7-0.8 300 7.0 (Badzian, Breval & Piotrowski, 2001)
SYNTHESIS Source: B lue penguin reportSchematics of a laser ablation set-up, reproduced from B. I. Yakobson and R.E. Smalley, American Scientist 85, 324 (1997).
METAL DOPED CARBON NANOTUBES Metal doping provides additional binding energy state of hydrogen. Transition metals doped- V, Ti, Pt and Pd. Storage condition : 30 atm, 300K Enhanced hydrogen storage capacity on doping, the reversible hydrogen storage capacity of doped nanotubes. April 2011 Journal of the American Chemical Society
CHALLENGES TO OVERCOME High accessible surface, large free pore volume & strong interactions- Three main demand for high hydrogen storage capacity. A more accurate & practical approach towards studying thermodynamics, Kinetics, Adsorption /Desorption of nanotubes. Mass production of carbon nanotubes with controlled microstructures at a reasonable cost.
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