In this work, activated multi-walled carbon nanotubes (Acti-MWNTs) with well-developed pore structures, a highly specific surface area, and higher hydrogen adsorption capacities due to CO(2) activation were prepared. The activation was performed at activation temperatures in the range of 500-1100 degrees C. The microstructure and crystallinity of the Acti-MWNTs were evaluated with a transmission electron microscope (TEM) and an FT-Raman spectrometer, respectively. The textural properties of the Acti-MWNTs were investigated by using a nitrogen gas sorption analyzer at 77 K. The hydrogen storage capacities of the Acti-MWNTs were investigated by BEL-HP at 298 K/100 bar. The hydrogen storage capacities of the Acti-MWNTs were enhanced to 0.78 wt.% by increasing activation temperatures to 900 degrees C, which resulted in the formation of a defective structure in the Acti-MWNTs. This result indicated that the CO(2) activation was one of the most effective methods to develop the textural properties, as well as to enhance the hydrogen storage capacities of MWNTs. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.