The interaction between fluorinated surface in the partially reduced nano-crystallite titanium dioxide (TiO2-x(F)) and MgH2 is studied for the first time. Compared with pristine MgH2 (416 °C), the onset desorption temperature of MgH2+5 wt.% TiO2-x(F) composite can be dramatically lowered to 189 °C. In addition, the composite exhibits remarkable dehydrogenation kinetics, which can release 6.0 wt.% hydrogen thoroughly within 6 min at 250 °C. The apparent activation energy for dehydriding is decreased from 268.42 to 119.96 kJ mol-1. Structural characterization and theoretical calculations indicate that the synergistic effect between multivalent Ti species, and the in situ formed MgF2 and MgF2-xHx is beneficial for improving the hydrogen storage performance of MgH2. Moreover, oxygen vacancies can accelerate the electron transportation and facilitate hydrogen diffusion. The study provides a novel perspective on the modification of MgH2 by fluorinated transition metal oxide catalyst.
Keywords: MgH2; catalyst; fluorine; hydrogen storage; oxygen vacancies.
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