Joshua W. Makepeace

Hydrogen production from ammonia using sodium amide.

This paper presents a new type of process for the cracking of ammonia (NH3) that is an alternative to the use of rare or transition metal catalysts. Effecting the decomposition of NH3 using the concurrent stoichiometric decomposition and regeneration of sodium amide (NaNH2) via sodium metal (Na), this represents a significant departure in reaction mechanism compared with traditional surface catalysts. In variable-temperature NH3 decomposition experiments, using a simple flow reactor, the Na/NaNH2 system shows superior performance to supported nickel and ruthenium catalysts, reaching 99.2% decomposition efficiency with 0.5 g of NaNH2 in a 60 sccm NH3 flow at 530 °C. As an abundant and inexpensive material, the development of NaNH2-based NH3 cracking systems may promote the utilization of NH3 for sustainable energy storage purposes.

Regeneration of sodium alanate studied by powder in situ neutron and synchrotron X-ray diffraction

The regeneration pathway of sodium alanate has been studied in detail by in situ synchrotron powder X-ray diffraction (SR-XRD) and powder neutron diffraction (PND). Rietveld refinement of the data has accurately determined the composition of all crystalline phases during the reaction process and shows definitively that Al initially reacts with NaH to form Na3AlH6, followed by the formation of NaAlH4 (before the total consumption of NaH) in two indiscrete reactions. During hydrogenation, an expansion of 0.6% of the Na3AlH6 unit cell is observed indicating towards the inclusion of Ti within the crystal lattice. This study promotes the recent development of next-generation sample holders and detectors that now enable the in situ diffraction measurement of hydrogen storage materials under relatively high gas pressures (>100 bar) and temperatures.