Thermodynamic analysis of ammonia storage materials

Abstract 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 ΔS0 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. ΔS0 linearly increased with the natural logarithm of the volume difference ΔV 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 ΔH0 was increased with ΔS0. Based on these experimental relations, we can calculate the ammonia vapor pressure PNH3 by ΔV.