Using multi-walled carbon nanotubes (MWCNTs), the present study focuses on their electrochemical hydrogen storage capacities. The results showed that the hydrogen desorption process is composed of two steps with voltages around -0.75 and -0.15 V. Hydrogen adsorption at -0.15 V took place at temperatures above 30 degrees C, and the amount of energy required for adsorbing hydrogen was 1.68 eV. The hydrogen storage capacity increased with increasing electrolyte temperature from 30 to 60 degrees C in both steps. The hydrogen storage capacity of the MWCNTs treated at different atmospheres showed that the decrease in the graphitization of MWCNTs led to the increase in hydrogen adsorption. The results also showed that the MWCNTs treated in a CO2 atmosphere had the highest hydrogen storage capacity at -0.15 V. (C) 2010 Elsevier Ltd. All rights reserved.