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Thermodynamic and kinetic improvement of MgH2 via the synergism of Al species and Nb-TiO2

Mengran Li,Jialing Gu,Qinke Tang,Jiabao Bai,Bin Cui,Ruoyu Ma,Yunfeng Zhu,Rui Shi,Yao Zhang,Jiguang Zhang,Yana Liu,Jun Wang,Zhixin Ba,Xiaohui Hu

Magnesium hydride (MgH 2 ) is a highly promising solid-state hydrogen storage material, but its application is hindered by sluggish kinetics and high operating temperatures. Currently, alloying and catalysis are effective strategies for improving the hydrogen storage performance of MgH 2 , but the designing of a hydrogen ab/desorption system which synergistically combines them remains a challenge. Herein, Mg Al solid solution and intermetallic compounds (Al species), and a spherical Nb-doped TiO 2 (Nb-TiO 2 ) were introduced into Mg/MgH 2 to enhance the hydrogen storage performance. Al species significantly enhanced the dehydrogenation thermodynamics of Mg 90 Al 10 - 15 at.% Nb-TiO 2 , while improving the hydrogen ab/desorption kinetics of the composite synergistically with the Nb-TiO 2 . Density functional theory (DFT) calculations revealed that the synergism of Al species and Nb-TiO 2 led to preferential adsorption of H atoms at the interfaces of Nb-TiO 2 and Mg 17 Al 12 , with abundant electron transfer. The dehydrogenation enthalpy ( ΔH ) of Mg 90 Al 10 - 15 at.% Nb-TiO 2 decreased from 80.86 (MgH 2 ) to 69.05 kJ/mol, while its hydrogen desorption apparent activation energy ( E a ) decreased from 146.40 (MgH 2 ) to 88.80 kJ/mol simultaneously. The composite could absorb 4.70 wt% H 2 within 2000 s at 200 °C and showed a dehydrogenation onset temperature of 209 °C. This work reveals a synergistic effect between alloying and catalysis, advancing both the performance enhancement strategies and the mechanistic understanding of Mg-based hydrogen storage materials.