Comprehensive hydrogen storage performance of Li–Mg–N–H hydrogen storage system co-doped with nano LaNi5 and SWCNTs: experimental and theoretical modification study

The Li–Mg–N–H (Mg(NH₂)₂–2LiH) system, as a high-capacity Mg-based metal hydrogen storage material (5.6 wt%), has broad prospects for in vehicle hydrogen storage applications, but it still has high hydrogen ab/desorption barriers. To improve its hydrogen storage performance, a nanohydrogen storage alloy was innovatively combined with Mg(NH₂)₂–2LiH, AB5 type nanohydrogen storage alloy LaNi₅ was prepared by co-precipitation method. Nano LaNi₅ and single-walled carbon nanotubes (SWCNTs) were co-doped into the Mg(NH₂)₂–2LiH system at a ratio of 10 wt% and 2 wt%, significantly enhancing the hydrogen storage performance of Mg(NH₂)₂–2LiH. The initial hydrogen ab/desorption temperatures of the co-doped system decreased from 110/130 °C to 45/85 °C. The release of by-product ammonia is significantly inhibited. 4.73 wt% H₂ can be ab/desorption in 150 min at 180/170 °C. Cycle tests show that the co-doped system can still maintain a hydrogen storage capacity of 4.75 wt% after ten hydrogen release cycles. Mechanism and density functional theory study have shown that during the hydrogen release process, partially hydrogenated LaNi₅ weakens the chemical bonding in Mg(NH₂)₂, promoted the dissociation of hydrogen from the Mg(NH₂)₂–2LiH system, while playing a dual role of "hydrogen overflow" and "hydrogen pump". SWCNTs act as auxiliary agents, helping to refine particle size and increase thermal conductivity. The synergistic effect of the two optimizes the comprehensive hydrogen storage performance of Mg(NH₂)₂–2LiH. This study provides a new research method for improving the comprehensive hydrogen storage performance of Mg-based metal hydrogen storage materials using rare earth element catalysts.

Graphical abstract