Improvement of Hydrogen Storage Properties of MgH2 Catalyzed by K2NbF7 and Multiwall Carbon Nanotube

A study has been conducted on the enhancement of the MgH2 hydrogen storage properties by the 10 wt % of K2NbF7 and 5 wt % of MWCNT. The composites are prepared by using the ball milling method. The dopants have significantly reduced the initial decomposition temperature of the MgH2-10 wt % K2NbF7-5 wt % MWCNT composite to 248 degrees C with a capacity of 6.2 wt %. The composite is able to absorb 5.2 wt % of hydrogen at 150 degrees C in 60 min. In addition, 6 wt % of hydrogen is released at 320 degrees C and 1 atm. The cycle performance study has shown that the absorption capacity of the codoped composite is reduced by 0.4 wt % while the milled MgH2 is reduced by 4.6 wt % after 5 cycles. The codoped composite decomposition activation energy is 75.9 kJ/mol, 59.4 kJ/mol lower than the milled MgH2. XRD analyses have observed the formation of MgF2, KH, and Nb after the heating process. The formed elements are believed to be the active species that helped to improve the hydrogen storage properties of the composite. In addition, the incorporation of MWCNT is believed to play a significant role on the improvement of the modified system.