Mechanochemistry and hydrogen storage properties of 2Li3N+Mg mixture

Abstract

The Li-Mg-N-H hydrogen storage system is a promising hydrogen storage material due to its moderate operation temperature, good reversibility, and relatively high capacity. In this work, the Li-Mg-N-H composite was directly synthesized by reactive ball milling (RBM) of Li 3 N and Mg powder mixture with a molar ratio of 2:1 under hydrogen pressure of 9 MPa. More than 8.8 wt% hydrogen was absorbed during the RBM process. The phases and structural evolution during the in situ hydrogenation process were analyzed by means of in situ solidgas absorption and ex situ X-ray diffraction (XRD) measurements. It is determined that the hydrogenation can be divided into two steps, leading to mainly the formation of a lithium magnesium imide phase and a poorly crystallized amide phase, respectively. The H-cycling properties of the as-milled composite were determined by temperature-programmed dehydrogenation (TPD) method in a closed system. The onset dehydrogenation temperature was detected at 125°C, and it can reversibly desorb 3.1 wt% hydrogen under a hydrogen back pressure of 0.2 MPa. The structural evolution during dehydrogenation was further investigated by in situ XRD measurement. It is found that Mg(NH 2 ) 2 phase disappears at about 200°C, phases coexist at even 300°C, revealing that the dehydrogenation process is step-wised and only partial hydrogen can be desorbed.

Mechanochemistry of Metal Hydrides: Recent Advances

“…To gain access to this system by mechanochemistry, lithium nitride and magnesium in molar ratio 2:1 were milled under hydrogen gas. The in situ hydrogen uptake curve displayed in Figure 7 reflects, as in the previous case, two consecutive reactions leading to full absorption in t m ≈ 2 h [146]. By structural analysis of deuterated compounds [131], they were assigned to the reaction scheme:2Li 3 N + Mg+ 2H 2 → Li 3 MgN 2 H + 3LiH Li 3 MgN 2 H + 3LiH + 3H 2 → Mg(NH 2 ) 2 + 6LiH…”

Liquid Channels Built-In Solid Magnesium Hydrides for Boosting Hydrogen Sorption

“…However, achieving safe and efficient hydrogen storage is a key challenge. Solid-state hydrogen storage has relatively high storage volume density and transport safety, which have become the focus of hydrogen storage research in recent years [7][8][9][10][11]. Metal hydrides are widely used as solid hydrogen storage materials because they can store large quantities of hydrogen under milder conditions in a reversible manner.…”