Thermodynamic analysis of ammonia storage materials

Thermodynamic analysis of ammonia storage materials such as metal halides, sodium borohydride, water and ammonium hydrogen sulfate was carried out to clarify the stability in the ammoniates. The standard entropy change Delta S-0 by ammonia absorption decreased with increase of the electronegativity of cation in metal chlorides and the electronegativity difference in metal halides. It was suggested that the stronger the binding energy, the smaller the entropy change by ammonia absorption. Delta S-0 linearly increased with the natural logarithm of the volume difference Delta V of the ammonia storage materials before and after ammonia absorption, whose slope is 11 times of the slope between the entropy and the natural logarithm of the volume of ideal gas. The standard enthalpy change Delta H-0 was increased with Delta S-0. Based on these experimental relations, we can calculate the ammonia vapor pressure P-NH3 by DV. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The thermodynamic analysis of ammonia storage materials revealed that the electronegativity of cations in metal chlorides and the electronegativity difference in metal halides play a crucial role in the stability of ammoniates. The stronger the binding energy, the smaller the entropy change caused by ammonia absorption. The standard entropy change Delta S-0 linearly increases with the natural logarithm of the volume difference Delta V of the ammonia storage materials.