Hydrogen storage properties of nano-CoB/CNTs catalyzed MgH2

Abstract

With CoCl2, NaBH4 and CNTs as the starting materials, the CoB/CNTs nanocomposites were successfully prepared and used as catalysts to improve the hydrogen storage properties of MgH2. CoB/CNTs catalysts were characterized by BET, SEM, and XRD. The results show that CoB/CNTs possesses high specific surface area. MgH2 doped with 10 wt% CoB/CNTs (MgH2+10 wt%CoB/CNTs) starts to release hydrogen at about 214 °C, and reaches a dehydrogenation peak at about 271 °C. These temperatures are 166 °C and 135 °C lower than that of commercial MgH2. The dehydriding/rehydriding kinetics of MgH2 are also remarkably improved by addition of CoB/CNTs. MgH2+10 wt%CoB/CNTs exhibits excellent isothermal hydrogen desorption kinetics at 300 °C. It can release around 5.5 wt% H2 within approximately 19 min, and can fully dehydride within 1 h. The maximum dehydridng rate reaches 22.9 wt%H2/h, which is 572 times faster than that of commercial MgH2. The activation energy of hydrogen desorption measured by Kissinger plot is estimated to be 89.1 kJ/mol for MgH2+10 wt% CoB/CNTs, which is reduced by 119.4 kJ/mol as compared to commercial MgH2. Moreover, The fully dehydrided MgH2+10 wt%CoB/CNTs product also shows excellent rehydriding properties, it can absorb up to 90% of hydrogen capacity within 20 s at 300 °C and 5 MPa H2. The catalytic mechanism is discussed.