H2 adsorption mechanism in Mg modified multi-walled carbon nanotubes for hydrogen storage

Abstract

Multi-walled carbon nanotubes (MWCNTs) with diameter of about 50 nm were synthesized using thermal chemical vapor deposition. We have investigated the influence of Mg doping to the MWCNTs on its hydrogen storage property. TEM micrographs showed that Mg was attached to the MWCNTs and discontinuous arrangement of the carbon walls was recognized in the MWCNTs. According to XPS and BET analyses, the surface functional groups and pore size of the Mg-MWCNTs are increased by interactions between the Mg and the MWCNT’s outer walls. The electrochemical discharging curves of the MWCNTs and Mg-doped MWCNTs revealed that the hydrogen storage capacity was 363 and 450 mAhg−1, respectively. Volumetric technique determined that the hydrogen storage capacity of the MWCNTs and Mg-MWCNTs was 0.7 and 1.5 wt%, respectively. There are likely a couple of mechanism for Mg metal that used as dopant to pure MWCNTs, one involves increasing of adsorption binding energy and desorption temperature due to increasing defect sites (oxygen functional groups), while the second explains by electron transfer from metal atoms to carbon atoms resulting in a considerable increase in both the adsorption binding energy and desorption temperature.