Thermal Stability of Ammonia Borane: A Case Study for Exothermic Hydrogen Storage Materials

A model to determine the thermal stability of chemical hydrogen storage materials was developed to predict the stability of ammonia borane at 50−60 °C, the extreme range of environmental temperatures for hydrogen storage materials in PEM fuel cell applications. Experimental data from differential scanning calorimetry measurements between 70 and 85 °C were used to develop isothermal and adiabatic reactivity models that could be extrapolated down to temperatures of interest. Results of the analysis show that solid ammonia borane is metastable in the 50−60 °C range, having stability against appreciable reaction on the order of a week at 60 °C and months at 50 °C. An adiabatic analysis is the most extreme case, and stability of many days under such extreme conditions indicates that solid ammonia borane may be suited to most hydrogen storage applications. This type of analysis is also applicable to other candidate hydrogen storage materials.