Thermodynamic assessment of the CeH and CeNi5 H system

Abstract

Interstitial metal hydrides (MHs) have attracted considerable attention in the field of hydrogen technology, particularly in the context of storage and compression applications. Because of their minor hysteresis effects, good cyclability, activation simplicity, and high volumetric storage density, ${\mathrm{LaNi}}_5$-based alloys are recognized as prominent candidates for hydrogen storage application. Additionally, the system’s thermodynamic and electrochemical properties can be modified to suit the requirements of a particular application by alloying specific substituents. To ascertain the thermodynamic effects of Ce addition within ${\mathrm{LaNi}}_5$, in this work the CeH and ${\mathrm{CeNi}}_5$ $H$ systems have been modeled with the CALPHAD method. For this reason, in this work, two different thermodynamic models have been developed and assessed using the same pressure-composition isotherms (PCIs) datasets obtained from literature and theoretical formation energies newly calculated employing periodic density functional theory (DFT). Direct comparison of the models against each other in terms of accuracy and physical plausibility revealed that extrapolation of thermodynamic properties to data-scarce regions is more reasonable with fewer model parameters and in agreement with other similar systems within the rare-earth ($\mathrm{RE}$) metal-hydride class. In addition, the ${\mathrm{CeNi}}_5$ $H$ system was investigated by assessing the ${\mathrm{(Ce)(Ni)}}_5{\left(\mathrm{V\; a,H}\right)}_7$ phase model, which could accurately predict hydrogen storage properties while being compatible with previously developed ${\mathrm{LaNi}}_5$ $H$ models. Ultimately, the models developed in this study may be employed and extended to describe multi-component $\mathrm{RE}$ $H$ systems and allow for thermodynamic computations that are highly desirable for accurate predictions of hydrogen absorption/desorption properties and degradation characteristics within the ${\mathrm{(La,Ce)Ni}}_5$ $H$ metal hydride family.