Insights into 2D graphene-like TiO2 (B) nanosheets as highly efficient catalyst for improved low-temperature hydrogen storage properties of MgH2

Abstract

The development of low temperature hydrogen storage system is crucial for the wide application of renewable energy. A key obstacle for this system is the lack of efficient catalysts, in which two-dimensional nanosheets have attracted considerable attention because of their unique properties. Herein, we synthesized graphene-like TiO2 (B), and applied them as a highly efficient catalyst to dramatically enhance the low temperature hydrogen storage performances of MgH2. The MgH2s–TiO2 (B) quickly absorbs 5.32 and 5.50 wt% H2 at low temperatures of 50 and 60 °C, respectively, which is superior to most of the previously catalyzed MgH2 composites. Moreover, MgH2–TiO2 (B) begins to desorb hydrogen at ~200 °C and release ~6.29 wt% H2 below 288 °C. Careful microstructure analyses reveal that TiO2 (B) nanosheets are reduced to metallic Ti nanoparticles and wrinkled Ti2O3 upon ball milling and (de)hydriding processes, which creates lots of boundary interfaces between MgH2 and Ti-based catalysts, thus facilitating the hydrogen diffusion. Besides, the in-situ formed Ti has the intermediate electronegativity between Mg and H, which could weaken the Mg–H bonds and decrease the dehydrogenation kinetic barriers. While in rehydrogenation, Ti nanoparticles act as effective heterogeneous nucleation agents of MgH2 nuclei, further promoting hydrogen absorption properties of MgH2–TiO2 (B). The present investigation provides clear evidence for remarkable catalytic effect of graphene-like TiO2 (B) on hydrogen absorption/desorption properties of MgH2, which is not only important for deeply understanding the mechanism, but also sheds lights for catalysis design towards practical low temperature hydrogen storage.