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Investigation on Parameters of Carbon Nanotubes Growth and Effect of Interaction between H2 Gas and their Surfaces and Determining Capacity of Hydrogen Storage

Reyhani, Ali | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39466 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Alireza; Nozad, Ahmad
  7. Abstract:
  8. In this study, growth of MWCNTs in form of thin film and powder for hydrogen storage was investigated. Different analytical techniques including SEM, TEM, STA, XRD, XPS, BET, BJH and Raman spectroscopy were applied to characterize the samples. The results showed that substrate, catalyst thickness and type of catalyst are influenced in yield of the growth, structure and quality of MWCNTs. The study has also indicated that MWCNTs grown on Fe-Pd bimetallic catalyst with 25-75 proportion had the highest growth yield. Moreover, decreasing of the growth temperature from 970 to 920 oC produced single-walled carbon nanotubes (SWCNTs) with high quality (IG/ID = 15.8) and low growth yield. Characterization of MWCNTs grown in powder form showed that Fe-Ni bimetallic catalyst with 50-50 proportion had the highest growth yield as compared with the other applied catalysts. Furthermore, by increasing of Fe-Ni catalyst to MgO support ratio, the quality and yield of MWCNTs increased but their diameter decreased. The MWCNTs were grown on the Fe-Ni/MgO with17.5-17.5/65 ratio posed the highest quality and 15-15/70 ratio had the lowest mean diameter. The results showed that yield of MWCNTs increased with increasing of growth temperature and the MWCNTs grown at 940 oC showed the highest quality as compared with other temperatures. Investigation on hydrogen storage by electrochemical and volumetric methods showed that the structure of MWCNTs, storage conditions and addition of transition metals to MWCNTs had critical roles in enhancement of hydrogen storage capacity. The purification of MWCNTs by HF is more effective on increasing of hydrogen storage capacity as a result of enlargement of pore volumes with size ≤ 2 µm and higher surface area of MWCNTs in comparison with the other applied acids. In addition, heat treatment of the purified MWCNTs in CO2 ambient had the highest hydrogen storage capacity in the channels due to increasing of the effective surface of nanotubes and their tip opening as compared with the other utilized ambient (N2, H2 and NH3). Investigation on MWCNTs grown on the Fe-Ni/MgO catalyst with different ratios indicated that decreasing of defects in the MWCNTs and reduction in their diameter resulted in decrease of hydrogen desorption temperature from the MWCNTs surface. Moreover, in electrochemical method, electrolyte temperature is more effective on increasing of hydrogen storage capacity due to increase of hydrogen diffusion rate in the MWCNTs. Inaddition, the electrochemical analysis showed that carbon islands and inner channels are two important sites for hydrogen chemisorption in the MWCNTs. Finally, adding of Co, Ca and Pd metals to the MWCNTs resulted in increase of hydrogen storage capacity and desorption temperature of adsorbed hydrogen due to increase of the amount of hydrogen chemisorptions on the MWCNTs
  9. Keywords:
  10. Multi-Walled Carbon Nanotube ; Hydrogen Storage ; Electrochemical Method ; Thermal chemical Vapor Deposition ; Volumetric Method

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