Ammonia-Storage in Lithium Intercalated Fullerides

Ammonia has been proposed as an indirect hydrogen carrier, where hydrogen is more easily stored than directly as hydrogen, motivating the search for ammonia-storage systems. Here we investigated the structural evolution of hyper-ammoniated lithium fulleride (ND3)yLi6C60 during ammonia desorption, using in-situ neutron powder diffraction as a function of temperature. In (ND3)yLi6C60, ammonia molecules are stored in their neutral state inside the inter-fullerene interstices and are coordinated to the intercalated Li ions, forming Li-ND3 clusters. Li6C60 is found to absorb up to 36.8 wt% ND3, which corresponds approximately to 14 ammonia molecules per C60. The ammonia release, studied either in-situ or ex-situ by means of manometric analyses and differential scanning calorimetry, takes place in two main steps, at 350-410 K and 500-540 K. These steps involve clear 1st order structural phase transitions and the process is reversible. These findings suggest that the system could be a good candidate for ammonia-storage.