Achieving both high hydrogen capacity and low decomposition temperature of the metastable AlH3 by proper ball milling with TiB2

AlH 3 is a metastable hydride with a high hydrogen density of 10.1 wt% and it can release hydrogen at a low temperature of 150–200 °C. Many additives (e.g., NbF 5 , TiF 3 , etc.) introduced by ball milling can significantly reduce the decomposition temperature of AlH 3 , but often simultaneously decrease the available hydrogen capacity. In this work, TiB 2 was introduced by ball milling to improve the decomposition performance of AlH 3 . AlH 3 + x wt% TiB 2 ( x = 2.5, 5, 7.5, 10) composites were prepared by ball milling, and the milling conditions were optimized. It was shown that the decomposition performance of the AlH 3 + 2.5 wt% TiB 2 ball milled at 225 rpm for 108 min is the best. The onset decomposition temperature is 78 °C, which is 60 °C lower than that of pure AlH 3 . The decomposition is terminated at 130 °C with 8.5 wt% of hydrogen is obtained. In addition, 5.3 wt% of hydrogen can be released within 200 min at constantly 80 °C. Under the same conditions, ball-milled AlH 3 can hardly release any hydrogen. The activation energy calculated by the Kissinger's method is 86 kJ mol −1 , which was 28 kJ mol −1 lower than that of ball-milled AlH 3 . Catalytic mechanism study reveals that the Al 2 O 3 layers on the surface of AlH 3 will interact with TiB 2 to form Al–Ti–B solid solution, resulting in lattice distortion. Through lattice activation, the decomposition kinetics of AlH 3 is improved. This work provides an efficient strategy to achieve both high hydrogen capacity and low decomposition temperature of metastable AlH 3 by proper ball milling with metal borides. Both high capacity and low decomposition temperature of AlH 3 were achieved by proper ball milling with TiB 2 which interacts with Al 2 O 3 surface layer to form Ti–Al–B solid solution. • AlH 3 was properly milled with TiB 2 . • Ball milling conditions and TiB 2 content were optimized. • Both high capacity and low decomposition temperature were achieved. • Al 2 O 3 react with TiB 2 to form Ti–Al–B solid solution. • Ti–Al–B solid solution contributes to the improvement of AlH 3 decomposition.