Excellent catalysis of TiO2 nanosheets with high-surface-energy {001} facets on the hydrogen storage properties of MgH2

Transition metal compounds are one of the highly efficient types of catalyst for improving the reaction kinetics of hydrogen storage materials. Among all the transition metals, titanium and its compounds show great catalytic effects on magnesium hydride. In this study, for the first time, TiO2 nanosheets with exposed {001} facets were synthesized and doped into MgH2. The TiO2 nanosheet (NS)-doped MgH2 showed superior kinetic performance and the lowest desorption temperature. The onset temperature of MgH2 + 5 wt% TiO2 NS for the release of hydrogen was 180.5 °C and the corresponding peak temperature was 220.4 °C, which are much lower than those of pure MgH2 and also distinctly lower than those of MgH2 + 5 wt% TiO2 nanoparticles (NP). For the isothermal dehydrogenation analysis, the MgH2 + 5 wt% TiO2 NS could release 6.0 wt% hydrogen within 3.2 min at 260 °C and desorb 5.8 wt% hydrogen within 6 min at 240 °C. It is worth noting that the MgH2 + 5 wt% TiO2 NS can even release 1.2 wt% hydrogen at a temperature as low as 180 °C within 300 min. The hydrogenation kinetics of MgH2 + 5 wt% TiO2 NS is also greatly improved, which could absorb hydrogen within only a few seconds at mild temperature. It can take up 3.3 wt% hydrogen at 50 °C and 5.4 wt% at 100 °C within 10 s. It is demonstrated that the tremendous enhancement in reaction kinetics of MgH2 can be ascribed to the nanometer size and highly active {001} facets of anatase TiO2. The higher average surface energy can significantly reduce the hydrogen desorption activation energy of MgH2 to 67.6 kJ mol-1, thus easily improving the hydrogen desorption properties.