Ammonium chloride-metal hydride based reaction cycle for vehicular applications

Abstract

© 2019 The Royal Society of Chemistry.

Hydrogen and ammonia have attracted attention as potential energy vectors due to their abundance and minimal environmental impact when used as a fuel source. To be a commercially viable alternative to fossil fuels, gaseous fuel sources must adhere to a wide range of standards specifying hydrogen delivery temperature, gravimetric capacity and cost. In this article, an ammonium chloride-metal hydride reaction cycle that enables the solid thermal decomposition products to be recycled using industrial processes is proposed. A range of metal hydrides and metal amides were reacted with ammonium chloride to determine the reaction pathways, products and overall feasibility of the cycle. The NH 4 Cl-MH (MH = metal hydride) and NH 4 Cl-MNH 2 (MNH 2 = metal amide) mixtures were heated to temperatures of up to 500 °C. The resulting products were experimentally characterised using temperature program desorption residual gas analysis, simultaneous differential scanning calorimetry and thermogravimetric analysis and in situ powder X-ray diffraction. Similar analysis was undertaken to determine the effect of catalyst addition to the starting materials. A maximum yield of 41 wt% of hydrogen and ammonia gas mixtures were released from the NH 4 Cl-MH materials at a maximum yield of 41 wt%. This exceptional gravimetric capacity allows for volumetric gas densities (363-657 kg m -3 ) that are much higher than pure NH 3 , H 2 or metal hydride materials. Overall, this reaction cycle allows carbon-neutral regeneration of the starting materials, making it a potential sustainable energy option.