Enhancing hydrogen storage performance of MgH2 with hollow Bi2Ti2O7 catalyst: Synergistic effects of Bi2Mg3 alloy phase and Ti polyvalency
Xiaoying Yang, Xinqiang Wang, Ruijie Liu, Yanxia Liu, Zhenglong Li, Wen‐Gang Cui, F. Z. Qi, Yaxiong Yang, Jian Chen, Hongge Pan
Abstract
The role of catalysts in enhancing the hydrogen storage kinetics of the Mg/MgH 2 system is pivotal. However, the exploration of efficient catalysts and the underlying principles of their design remain both a prominent focus and a significant challenge in current research. In this study, we present a bimetallic oxide of Bi 2 Ti 2 O 7 hollow sphere as a highly effective catalyst for MgH 2 . As a result, the Bi 2 Ti 2 O 7 -catalyzed Mg/MgH 2 system lowers the hydrogen desorption initiation temperature to 194.3 °C, reduces the peak desorption temperature to 245.6 °C, decreases the dehydrogenation activation energy to 82.14 kJ·mol −1 , and can absorb 5.4 wt. % of hydrogen within 60 s at 200 °C, demonstrating outstanding hydrogen ab/desorption kinetics, compared to pure MgH 2 . Additionally, it can maintain a high hydrogen capacity of 5.2 wt. %, even after 50 dehydrogenation cycles, showing good cycle stability. The characterization results show that the high-valent Bi and Ti in Bi 2 Ti 2 O 7 are reduced to their low-valent or even zero-valent metallic states during the dehydrogenation and hydrogenation process, thus establishing an in-situ multivalent and multi-element catalytic environment. Density functional theory calculations further reveal that the synergistic effects between Bi and Ti in the Bi-Ti mixed oxide facilitate the cleavage of Mg-H bonds and lower the kinetic barrier for the dissociation of hydrogen molecules, thereby substantially enhancing the kinetics of the Mg/MgH 2 system. This study presents a strategic method for developing efficient catalysts for hydrogen storage materials by harnessing the synergistic effects of metal elements.