Design of multicomponent alloys with C14 laves phase structure for hydrogen storage assisted by computational thermodynamic

Abstract

Design methods with predictive properties modeling are paramount tools to explore the vast compositional field of multicomponent alloys. The applicability of an alloy as a hydrogen storage media is governed by its thermodynamic properties, which can be represented by pressure-composition-temperature (PCT) diagrams. Therefore, the prediction of PCT diagrams for multicomponent alloys is fundamental to design alloys with optimized properties for hydrogen storage applications. In this work, a strategy to design C14-type Laves phase multicomponent alloys for hydrogen storage assisted by computational thermodynamic is presented. Since electronic and geometrical factors play an important role in the formation and stability of multicomponent Laves phase, valence electron concentration (VEC), atomic radius ratio (rA/rB), and atomic size mismatch (δ) are initially considered to screen a high number of compositions and find alloy systems prone to form Laves phase structure. Then, CALPHAD method was employed to investigate the phase stability of alloys of the (Ti, Zr or Nb)(V, Cr, Mn, Fe, Co, Ni, Cu, or Zn)2 system, resulting in 440 alloys prone to solidify as C14 Laves phase structure. In addition, we present a thermodynamic model, which allowed calculating the PCT diagrams of the suggested C14 Laves phase alloys based solely on the alloy's composition. For these calculations, the entropy and enthalpy of hydrogen solution in the C14 Laves phase were modelled considering that hydrogen solid solution occurs only at the A2B2-type interstitial sites of the C14 Laves phase structure. Therefore, the room temperature PCI diagrams of 440 C14 Laves phase multicomponent alloys were calculated. Experimental pressure-composition-isotherm (PCI) diagrams of six C14 Laves phase alloys were compared against the calculated ones. Although the PCI curve shapes were not perfectly predicted for some alloys, the order of magnitude of the equilibrium pressure for all the tested alloys were well predicted. The results show that C14 Laves phase multicomponent alloys within a wide range of equilibrium pressure at room temperature can be obtained, being promising candidates for different hydrogen storage applications, such as room temperature tanks, hybrid tanks and Ni-metal hydrides batteries.