Facile Uptake and Release of Ammonia by Nickel Halide Ammines

Although major difficulties are experienced for hydrogen- storage materials to meet performance requirements for mobile applications, alternative fuel cell feedstocks such as ammonia can be stored in the solid state safely at high capacity. We herein describe the NiX2 -NH3 (X=Cl, Br, I) systems and demonstrate their exceptional suitability for NH3 storage (up to 43 wt % NH3 with desorption that begins at 400 K). The structural effects that result from the uptake of NH3 were studied by powder X-ray diffraction (PXD), FTIR spectroscopy and SEM. NH3 release at elevated temperatures was followed by in situ PXD. The cycling capabilities and air stability of the systems were also explored. NH3 is released from the hexaammines in a three-step process to yield the diammine, monoammine and NiX2 dihalides respectively and (re)ammoniation occurs readily at room temperature. The hexaammines do not react with air after several hours of exposure.