Improved hydrogen storage properties of MgH2 by the addition of TiCN and its catalytic mechanism

Abstract

The hydrogen storage properties of MgH2–x wt%TiCN (x = 5, 10, 15) composites were systematically investigated and the results show that the addition of TiCN can effectively improve the de/rehydrogenation kinetics of MgH2. Taken the onset dehydrogenation temperature and isothermal de/rehydrogenation kinetics into consideration, the MgH2–10 wt% TiCN composite was shown to have the best performance. It was found that the MgH2–10 wt% TiCN composite could release 4 wt% H2 in 17.3 min at 300 °C while the as-synthesized MgH2 could not release any hydrogen under the same condition. Besides, the MgH2–10 wt% TiCN composite could absorb 4.63 wt% H2 under 3.2 MPa hydrogen pressure at 300 °C within 20 s. Compared with as-synthesized MgH2, the activation energy of the MgH2–10 wt% TiCN composite was significantly decreased from 183.76 ± 10 to 106.82 ± 5 kJ/mol. X-ray diffraction analysis revealed that the TiCN remained stable during the ball milling and the following de/rehydrogenation cycle. The catalytic mechanism was also proposed that the TiCN particles absorbed on MgH2 not only served as charge transfer centers and accelerated the hydrogen incorporation and dissociation rate but also provided more diffusion channels for hydrogen, which contributed to the good de/rehydrogenation properties of MgH2.