Hetero-atoms as activation centers for hydrogen absorption in carbon nanotubes

Carbon materials should have specific centers for hydrogen adsorption/absorption. The role of heteroatom substitution in carbon nanotubes as an activator has been identified by Density Functional Theory. The effect of various hetero-atoms like nitrogen, phosphorus, sulphur and boron for hydrogen activation and their geometrical positions has been recognized as the one of the possible reasons for easy hydrogenation. Experimentally, nitrogen and boron containing carbon nanotubes have been synthesized by using template method. The hydrogen absorption capacity of these materials has been evaluated. It is shown that, there is a need to stabilize nitrogen in the carbon nanotube framework for reproducible hydrogen uptake. In the case of boron containing carbon nanotubes, two different chemical environment of boron facilitates hydrogen interaction. They exhibit a maximum of 2 wt.% of hydrogen storage capacity at 80 bar and 300 K. This configuration has a bearing in hydrogen sorption characteristics.