Electrochenucal study of hydrogen storage mechanism of carbon nanotubes

Purified multi-walled carbon nanotubes (MWNTs) with an average outer diameter of 6 rim and a high purity of 95 w/%, synthesized by a floating catalyst method, were employed for electrochemical hydrogen storage experiments, which were conducted at room temperature and atmospheric pressure. A discharge capacity of 739 mAh/g, corresponding to a hydrogen storage capacity of 2.68 w/% normalized to the weight of MWNTs, was obtained. The self-discharge experimental results show that the cohesive force between hydrogen and the MWNTs is so weak that hydrogen can easily escape from the MWNTs when the charge process stops, and this result implies that the mechanism for electrochemical storage of hydrogen in MWNTs may be mainly physical adsorption. In addition, the volumetric measurement results also support a physical adsorption mechanism for gas phrase hydrogen storage in the same purified MWNTs. Therefore, electrochemical hydrogen storage and gas-phase storage of hydrogen in purified MWNTs share the same mechanism, i.e. mainly physical adsorption.