Consistency between the experimental formation entropy of MgH2 and the spectroscopic entropy based on the third law of thermodynamics

摘要

In the Mg-H system, large discrepancies exist between the reported thermodynamic parameters (standard enthalpy and entropy of formation, Delta H-f degrees and Delta S-f degrees, respectively) calculated for the equilibrium pressures in pressure-composition-temperature (PCT) curves. The reported values differ by as much as 15%. Moreover, the thermodynamic parameters evaluated from hydrogenation and dehydrogenation have large discrepancies. Such discrepancies in the thermodynamic parameters can arise either from a failure to reach true equilibrium in the case of slow hydrogen desorption kinetics or from a failure to measure the true temperature in the case of PCT curves.