Mechanism of hydrogenation and dehydrogenation in Mg/Cu9Al4 @Mg and MgH2/Cu9Al4 @MgH2: A DFT and experimental investigation

Abstract

The Cu9Al4 intermetallic has been found to enhance the hydrogenation and dehydrogenation capabilities of Mg. However, its impact on kinetics is unclear. In the present work, the hydrogenated and dehydrogenated mechanism were investigated by experimental and theoretical methods, including Density Functional Theory (DFT) and ab initio molecular dynamic (AIMD) simulations. Experimental results show that the addition of Cu9Al4 IMC can promote the hydrogenation and dehydrogenation kinetics of Mg, which the dehydrogenation rate of Cu9Al4 @MgH2 is 3 times that of MgH2. AIMD simulations illustrate that the electron properties of Cu9Al4 @Mg and Cu9Al4 @MgH2 are different from that of pure Mg and MgH2, which lead to the change of hydrogenated and dehydrogenated mechanism in Mg/Cu9Al4 @Mg and MgH2/Cu9Al4 @MgH2. Moreover, the diffusion coefficient of H atoms in Cu9Al4 @MgH2 is 4 times that in MgH2. The addition of Cu9Al4 IMC decreases the particle size of Cu9Al4 @Mg during ball milling and induces lattice distortion of Cu9Al4 @MgH2 during the dehydrogenation process. These changes may contribute to the enhancement of the dehydrogenation rate in Cu9Al4 @MgH2. This work complements the mechanism of IMC for improving the performance of hydrogen storage materials and provides a theoretical basis for the development of next-generation solid-state hydrogen storage materials.