CNTs decorated with CoFeB as a dopant to remarkably improve the dehydrogenation/rehydrogenation performance and cyclic stability of MgH2

Abstract

The chain-like carbon nanotubes (CNTs) decorated with CoFeB (CoFeB/CNTs) prepared by oxidation-reduction method is introduced into MgH2 to facilitate its hydrogen storage performance. The addition of CoFeB/CNTs enables MgH2 to start desorbing hydrogen at only 177 °C. Whereas pure MgH2 starts hydrogen desorption at 310 °C. The dehydrogenation apparent activation energy of MgH2 in CoFeB/CNTs doped-MgH2 composite is only 83.2 kJ/mol, and this is about 59.5 kJ/mol lower than that of pure MgH2. In addition, the completely dehydrogenated MgH2−10 wt% CoFeB/CNTs sample can start to absorb hydrogen at only 30 °C. At 150 °C and 5 MPa H2, the MgH2 in CoFeB/CNTs doped-MgH2 composite can absorb 6.2 wt% H2 in 10 min. The cycling kinetics can remain rather stable up to 20 cycles, and the hydrogen storage capacity retention rate is 98.5%. The in situ formation of Co3MgC, Fe, CoFe and B caused by the introduction of CoFeB/CNTs can provide active and nucleation sites for the dehydrogenation/rehydrogenation reactions of MgH2. Moreover, CNTs can provide hydrogen diffusion pathways while also enhancing the thermal conductivity of the sample. All of these can facilitate the dehydrogenation/rehydrogenation performance and cyclic stability of MgH2.