Recent development on hydrogen storage properties in metal-N-H systems

In this paper, we review our recent results on hydrogen storage properties in light metals(M)-nitrogen(N)-hydrogen(H) systems prepared by mechanochemical method. At first, the composite mixture of LiH and LiNH₂ doped with TiCl₃ as a catalyst was prepared by ball milling for 2 h under a H₂ gas pressure of 1 MPa. The TDS profile indicated that ∼6 mass% H₂ was desorbed by the reaction LiH + LiNH₂ ↔ Li₂NH + H₂ in the temperature range from 150 to 250 °C under a He gas flow at a heating rate of 5 °C min^-1, but the H-desorption equilibrium pressure P_H2 was ∼0.1 MPa at 250 °C. This temperature is too high for onboard use, indicating that further improvement is necessary to destabilize the above H-storage reaction. For that, we clarified the H-desorption mechanism by the isotopic exchange experiments, on the basis of which we designed a new Li-Mg-N-H composite system with the reaction 8LiH + 3Mg(NH₂)₂ ↔ 4Li₂NH + Mg₃N₂ + 8H₂. This composite materials desorbed ∼7 mass% H₂ in the range from 120 to 200 °C and the H-desorption equilibrium pressure P_H2 was higher than 5 MPa at 200 °C, indicating that this system has an excellent potential for onboard applications.