Study on Hydrogen Storage of Modified Multi-Walled Carbon Nanotubes

• Main Authors: Chien-Hung Chen, 陳建宏
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/98513270416726912654

博士 === 雲林科技大學 === 工程科技研究所博士班 === 96 === Abstract A systematic study of hydrogen storage in multi-walled carbon nanotubes (MWCNTs) was investigated in this study. The MWCNTs were modified by acidic solution washing, high temperature annealing, KOH activation, KOH impregnation and Co impregnation. The hydrogen capacity of MWCNTs was determined by both thermal gravimetric and volumetric approaches. By thermal gravimetric approach, the hydrogen capacity of MWCNT samples was obtained from the weight changes under heating/cooling cycles between 303 K and 773 K. By volumetric method, the hydrogen capacity in MWCNTs was obtained according to the pressure changes at 77-90 K and under pressure below 760 torr. Surface structures of MWCNTs were characterized by a high resolution transmission electron microscope (HRTEM, JEOL, JEM-2010 type), an X-ray photoelectron spectroscopy (XPS, Thermo VG, ESCAlab 250), an X-ray diffractometer (XRD, RIGAKU, D/MAX-2200) and a Raman spectrometry (Tokyo Instruments, NANOFINDER 30). Nitrogen adsorption isotherm of MWCNTs was measured by a gas adsorption apparatus (QUANTACHROME, AUTOSORB-1) at 77 K. From the experimental results, firstly, the potassium metal can be used to promote the hydrogen storage capacity in MWCNTs. The highest capacity of the KOH modified MWCNTs determined by the thermal gravimetric method is 4.47 wt.% . The causes of hydrogen storage enhancement were attributed to the surface defects, the adsorption by potassium metal and the hydrogen spillover by residual metal Co. Secondly, the structure characteristics (e.g. crystallization and functional groups) of MWCNTs after KOH activation did not significantly change. After appropriate KOH activation, hydrogen capacity of MWCNTs was enhanced and attributed to surface physical characteristics involving specific surface area, pore volume and defects feature. Thirdly, hydrogen spillover by Co metal was adequately explained hydrogen storage enhancement in MWCNTs. The defect or cavity sites on the external surface of CNTs played an important role in promoting hydrogen atom migration from external surface into the interplanar spacing between graphite layers. Finally, the hydrogen adsorbed sites in MWCNTs with defect feature was suggested to be the micro pores within the defective cavities on the surface. The hydrogen adsorption behavior in MWCNTs was based on the volume filling theory. Furthermore, it is also found that the isosteric heat of hydrogen adsorption was affected by the MWCNT’s defect feature.