Hydrogen carrier by ammonia borane-ammonia system with low-vapor pressure

Abstract

Ammonia (NH3) absorption of ammonia borane (AB) was evaluated as potential hydrogen and/or NH3 storage system for hydrogen transportation in this work. The thermodynamic properties of the AB-NH3 system, the physical properties such as density and kinematic viscosity, and the stability of AB stored in liquid NH3 were evaluated. The enthalpy and entropy values of the AB-NH3 system were determined to be −19.87 kJ/mol and 67.76 J/mol·K, respectively. The structural identification of AB after NH3 removal revealed that NH3 can be removed completely from AB. Both volumetric and gravimetric hydrogen densities of the AB-NH3 system were higher than those of liquid NH3 under the vapor pressure of 0.1 MPa. The kinematic viscosity of the AB-NH3 system is moderate, which is easy to handle. According to the stability evaluation from 11B NMR results, high stability for both AB and NH3 was confirmed at room temperature. The study also demonstrates that storing AB in liquid NH3 is efficient for hydrogen transportation although temperature control is important for maintaining AB purity. Overall, the findings provide new insights into the AB-NH3 system and its potential applications in energy storage.