Influence of different cone angles for hydrogen adsorption of cup-stacked carbon nanotube: A DFT study

Many phenomena remain to be investigated regarding the micro adsorption kinetics of hydrogen storage in different carbon nanomaterials. The hydrogen adsorption behaviour on the wall surface of the conical graphene layers (CGL) of three kinds of different cup-stacked carbon nanotubes (CSCNTs) is investigated using density functional theory (DFT). Furthermore, Pt decoration of the CGL wall was also investigated. The hydrogen adsorption result of the Pt-CGL is examined through the charge transfer and electron density difference approach. The optimisation results show that as the cone angle increases, the hydrogen adsorption capacity on the outside of the CGL wall increases gradually. In contrast, the hydrogen adsorption capacity on the inside of the wall decreases as the cone angle increases. The adsorption energy (E_ads) of intrinsic CGL can only reach 5 kJ/mol, and the E_ads of defective CGL can reach 10 kJ/mol. In contrast, the E_ads of Pt-CGL can reach more than 30 kJ/mol, indicating that the hydrogen adsorption capacity of the CGL can be effectively increased by the Pt atom decoration, which can meet the adsorption energy target of hydrogen storage material formulated by the United States Department of Energy (DOE).