Application of nitrogen-doped graphene-supported titanium monoxide as a highly active catalytic precursor to improve the hydrogen storage properties of MgH2

Abstract

MgH2 has broad prospects in energy storage applications; however, its poor thermodynamic properties and slow hydrogen absorption and desorption rates are unsuitable for commercial needs. In the present work, TiO@N-C (denoted as TTONC), a highly active catalytic precursor, was employed to improve the hydrogen storage properties of MgH2. The TTONC-catalyzed MgH2 could uptake hydrogen at room temperature, and the onset dehydrogenation temperature of TTONC-catalyzed MgH2 was 94 °C lower than that of pristine MgH2 (∼300 °C). Dehydrogenated TTONC-catalyzed MgH2 had a capacity retention rate of 95.2% after 50 hydrogen absorption-desorption cycles. The dehydrogenation and hydrogenation apparent activation energies of MgH2-TTONC were 90.5 kJ.mol−1 and 52.7 kJ.mol−1, respectively. The catalytic mechanism analysis revealed that the in situ formed Ti generated TiH2 in the hydrogenation process, and Ti/TiH2 acted as a hydrogen pump to diffuse hydrogen atoms in the hydrogen absorption/desorption process. The formation of stable CN layers with carbon structural defects on the surface of MgH2 inhibited the fragmentation and agglomeration of MgH2 particles, and they served as nucleation sites to enhance hydrogen diffusion. Hence, the dehydrogenation/hydrogenation properties and cyclic stability of MgH2 were greatly enhanced by the addition of TTONC.