Amorphous Ti³⁺ oxide formed in situ from Ti-MOF nanosheets as a highly efficient catalyst for enhancing hydrogen storage kinetics of MgH2

In this work, a Ti-MOF catalyst (Ti-MOF-3) with a stacked nanosheet morphology was successfully synthesized, which significantly enhances the de/hydrogenation kinetics of MgH 2 . The initial and peak dehydrogenation temperatures of MgH 2 –5 wt.% Ti-MOF-3 composite are reduced to 203.9 °C and 272.1 °C, respectively. Specifically, this composite can rapidly release 5.82 wt.% H 2 within 1200 s at 275 °C, and absorb 5.38 wt.% H 2 within 2400 s at 100 °C. The nanosheet structure exhibits a large specific surface area, which increases the number of catalytic sites and improves the interaction interface with MgH 2 during the ball milling process. During the first dehydrogenation process, amorphous multivalen Ti oxides are in situ formed, with Ti 3+ oxide content as high as 51.38%. Theoretical calculation results show that Ti 3+ oxide serves a crucial catalytic function to enhance the hydrogen storage performance of MgH 2 by significantly reducing the hydrogen adsorption energy and weakening the Mg-H bonds. In addition, the amorphous state can regulate the electronic distribution to offer more catalytic sites, enhancing the catalytic activity. Therefore, the considerable improvement of the hydrogen storage kinetics should be attributed to the nanosheet morphology of Ti-MOF-3 and the in situ formation of amorphous Ti 3+ oxide. This work provides valuable insights into the development of advanced MOF-based catalysts for the catalytic modification of magnesium-based hydrogen storage alloys.