Thermodynamic Modeling of the Ni–H System

Abstract

A new thermodynamic assessment of the Ni-H system has been carried out, providing a complete description valid up to 6×10 9 Pa of this system at the center of hydrogen storage issues. The study includes the hydride formation reaction and the presence of a miscibility gap in the fcc interstitial solid solution of hydrogen in nickel. In addition to a complete literature review, first principles calculations were carried out and combined with other modeling approaches. The Cluster Expansion Method allowed to describe the energetic interactions between atoms leading to the miscibility gap in the fcc solid solution. Besides, the compressibility at high pressure was characterized for each phase including the condensed phases. For this purpose, a specific high pressure model was assessed with the contribution of quasi-harmonic phonon calculations. The obtained consistent model allows to characterize entirely the thermochemical behavior of the Ni-H system.

Systematic First-Principles Study of Binary Metal Hydrides

“…The hydride formation pressures at 300 K were determined using the equations of state of Joubert for gaseous hydrogen, valid up to 10 11 Pa and 1000 K 33 and approximating the entropy of formation by the opposite of the gas entropy. Considering the compressibility of the solid phases (hydride and metal) requires heavy calculations and it has been observed in a previous study on NiH 34 that the contributions of the hydride and the metal tend to oset each other. Therefore, the resulting energy contribution is not predominant compared to that of the compressibility of the gas phase and was neglected in the present study.…”

“…80 When the volumes of the condensed phases are aected, more complex models are needed, which involve the corresponding volume variations with T and P (see e.g. the treatment done in [ 34]).…”

Pd–H and Ni–H phase diagrams using cluster variation method and Monte Carlo simulation

“…The thermodynamic modeling Calphad method [30,31] was only recently employed to describe the thermodynamic behavior of the system, gathering all the available experimental data and adding theoretical results from the Cluster Expansion Method (CEM) [32].…”

“…Phase diagrams and spinodals of Pd-H and Ni-H systems obtained by CVM. Comparison with the Calphad models[29,32] and experimental data.…”

Modification of Lu's (2005) high pressure model for improved high pressure/high temperature extrapolations. Part II: Modeling of osmium–platinum system at high pressure/high temperature

“…The description of systems at high pressure is very interesting and the Calphad method is very powerful to achieve this if proper models are used. Many pure elements in condensed phases are described in the literature with one or another model: Mo [57], Mn and Ni [58], Cu [59], Al and Fe [60], Ag, Au, Cu, Mo, Nb, Pd, Pt, Ta, V and W [61], Hf [62], Al and Pt [63], Cu and Zn [64], Al and Si [65], Ni [66], Pt [67]. Much fewer descriptions of binary or higher order systems are available: Mn-Ni [58], C-Fe [68], Al-Si [65], H-Ni [66], Al-Cu-Mg [69], Bi-Sb, Bi-Sn and Pb-Sn [70].…”