Carbon Nanotubes as Future Energy Storage System

Hydrogen is considered to be a clean energy carrier. At present the main drawback in using hydrogen as the fuel is the lack of proper hydrogen storage vehicle, thus on-going research is focused on the development of advance hydrogen storage materials. Many alloys are able to store hydrogen reversibly, but the gravimetric storage density is too low for any practical applications. Theoretical studies have predicted that interaction of hydrogen with carbon nanotubes is by physisorption of hydrogen on the exterior and in the interior surfaces. Hence the CNTs appear to be the ultimate solution due to their chemical stability, large surface area, low density and hollowness. Recent studies indicate that the physisorption on pure CNTs may not be a feasible method of storing hydrogen. Hence, the functionalization of CNTs with metal hydrides is a subject of increasing scientific interest, to improve the hydrogen storage capacities. Lithium borohydride is a complex hydride that is received considerable attention due to its high gravimetric and volumetric hydrogen storage capacities. Our experimental investigation deals with the hydrogenation of SWCNTs functionalized with borane and also we have studied SWCNTs with different metal oxides composite like TiO2, SnO2 and WO3. SWCNTs functionalization with borane was carried out by drop casting method. SWCNTs-metal oxide composite was prepared by both drop casting method and electron beam evaporation method. These results were discussed in detail in the present work. Studies were carried out with the aim to achieve higher storage capacity of hydrogen. It is found that the maximum storage capacity of 4.77 wt.% was observed for the SWCNTs functionalized with borane. The achieved hydrogen storage capacity in this investigation is close to the U.S. DOE target.