Evaluation of the enthalpy change due to hydrogen desorption for M–N–H (M = Li, Mg, Ca) systems by differential scanning calorimetry

• ΔH of metal-N-H system dehydrogenation was evaluated by differential scanning calorimetry.
• Cell constant of DSC apparatus was determined by reference sample measurement.
• Extent of dehydrogenation was determined by thermogravimetry
• ΔH of complex hydrogen desorption can be evaluated by analysing DSC profile.
• Time required for ΔH estimation is much shorter than conventional methods.

The enthalpy changes (ΔH) corresponding to the hydrogen desorption reactions LiNH2 + LiH → Li2NH + H2, 3 Mg(NH2)2 + 8LiH → Mg3N2 + 4Li2NH + 8H2, Ca(NH2)2 + 2LiH → CaNH + Li2NH + 2H2, and 2LiNH2 + CaH2 → CaNH + Li2NH + 2H2 were evaluated using differential scanning calorimetry (DSC) and were estimated to be 66.5, 47.1, 47.7, and 48.0 kJ/mol H2, respectively. To obtain accurate and precise values of ΔH, the cell constant of the DSC apparatus was determined using a reference sample, which has a similar hydrogen desorption temperature to those of the above systems. Furthermore, the accurate sample amount corresponding to the hydrogen desorption was estimated from the weight loss obtained by thermogravimetry (TG). It is clear from the experimental results that evaluation using DSC and TG measurements is a useful technique to obtain accurate ΔH values for the hydrogen desorption systems with complicated reaction processes. In addition, the required experimental time is shorter than those of conventional techniques using a volumetric method.