Ammonia-storage in lithium intercalated fullerides

Abstract

Ammonia has been proposed as an indirect hydrogen carrier, as solid-state ammonia-storage could be easier than directly absorbing hydrogen in materials. Here we investigate the structural evolution of hyper-ammoniated lithium fullerides (ND₃)_yLi₆C₆₀ during ammonia desorption, using in-situ high intensity neutron powder diffraction. 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 to approximately 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, respectively. This corresponds to two clear 1^st order structural phase transitions and the absorption process is partially reversible. These findings suggest that the system could be a good candidate for ammonia-storage applications.