A <sub>2</sub> B <sub>7</sub> ‐type La–Mg–Ni alloys prepared by Mg thermal diffusion for improved hydrogen storage performance
Yongxi Zhang, Guanjiu Wu, Jing Gu, Hong-Xing Kang, Yuan Li, Di Zhou, Wenfeng Wang, Lu Zhang, Shumin Han
Abstract
Abstract A novel approach based on thermal diffusion was used to achieve controllable Mg content in A 2 B 7 ‐type La–Mg–Ni‐based alloys. The formation mechanism of the A 2 B 7 ‐type phase as a result of the thermal diffusion process and the effect of Mg content on hydrogen storage performance were investigated. X‐ray diffraction (XRD) patterns and Rietveld refinement results showed that increased Mg transformed the LaNi 5 phase in the La 0.74 Sm 0.03 Y 0.23 Ni 4.32 Al 0.04 precursor alloy into a superlattice structure. Scanning electron microscopy (SEM) images showed that Mg was evenly distributed in the alloy bulk. Mg in the superlattice significantly inhibited the phase decomposition of the superlattice structure during the hydrogen absorption/desorption cycles. An A 2 B 7 ‐type La 0.57 Sm 0.02 Y 0.18 Mg 0.23 Ni 3.38 Al 0.03 alloy composed of Gd 2 Co 7 and Ce 2 Ni 7 phases was successfully synthesized. The pressure–composition isotherm profiles showed that the alloy had a hydrogen storage capacity as high as 1.73 wt%, with good cycling stability. After 50 cycles of hydrogen absorption/desorption, the alloy retained a hydrogen storage capacity of 1.45 wt%, with a capacity retention rate of up to 84.28%. The Mg thermal diffusion process thus provides a new approach for the controlled preparation of La–Mg–Ni‐based alloys.