Measurement of thermochemical properties of some metal hydrides – Titanium (Ti), misch metal (Mm) and lanthanum (La) based alloys

In this manuscript, the estimation of thermochemical properties such as enthalpy of formation (ΔH) and entropy of formation (ΔS) during hydriding and dehydriding reactions of three titanium (Ti), five misch metal (Mm) and eight lanthanum (La) based metal hydride alloys are presented. van't Hoff plots of the selected metal hydride alloys are constructed using the Pressure–Concentration–Temperature (PCT) characteristics measured at different operating temperatures. Reaction enthalpies during hydriding and dehydriding processes are expressed as a function of hydrogen storage capacity by a polynomial equation of order three. The average enthalpy of formation during dehydriding process of the investigated titanium and lanthanum based alloys are about 3–18% higher than their respective hydriding enthalpies. While, dehydriding enthalpies of LmNi4.49Al0.205Mn0.205Co0.1 and MmNi4.85Al0.15 are about 26.5% and 40% higher than their respective hydriding enthalpies. The variation in reaction enthalpies during the initial and final stages of hydriding process of titanium based alloys is in the range of 7–9%, while the respective ranges for misch metal and lanthanum based alloys are about 3–7.5% and 2.1–8.5%, respectively.

► Measured the PCT characteristics of some Ti, Mm and La based hydride alloys.
► Estimated the ΔH and ΔS of some Ti, Mm and La based hydride alloys.
► Reaction enthalpies are expressed as a function of hydrogen storage capacity.
► Variation in hydriding enthalpy of Ti based alloys is in the range of 7–9%.
► Dehydriding ΔH's of Mm alloys are 26–40% higher than their hydriding ΔH's.