Decomposition Kinetics of Lithium Amide and Its Implications for Hydrogen Storage

Abstract

ABSTRACTKinetics of the lithium amide (LiNH2) decomposition reaction 2 LiNH2 → Li2NH + NH3 were determined using thermogravimetric analysis (TGA). LiNH2 is a primary component of the hydrided state of Li3N- and Li2NH-based storage materials. Its decomposition by ammonia release, and the resulting degradation of hydrogen storage capacity, has important implications for the durability of Li-N-H storage systems. Fine powders of LiNH2 were prepared by ball milling for 20 min. Kinetic parameters were extracted from a set of TGA weight loss curves taken at different heating rates between 1 and 20°C/min, and the activation energy Ea was determined to be 124 kJ/mole. Although decomposition occurs slowly below 300°C, isothermal TGA measurements on Li3N demonstrate that its cumulative effect is large in real Li-N-H systems, where LiNH2-containing hydrided material is held at elevated temperature under dynamic gas flow.