Design of multicomponent alloys with single c14 laves phase for hydrogen storage assisted by thermodynamic computational methods

Abstract

Multicomponent alloys with C14 Laves phase structure hold great promise as hydrogen storage materials due to their capacity for reversible absorption of significant hydrogen amounts at room temperature with excellent kinetics. Design methodologies that incorporate predictive property modeling is essential for effectively navigating the vast compositional space of multicomponent alloys. The effectiveness of an alloy as a hydrogen storage media depends on its thermodynamic properties, often visualized through pressure-composition-temperature (PCT) diagrams. Therefore, the prediction of PCT diagrams for multicomponent alloys is a paramount factor to design alloys with optimized properties for hydrogen storage applications. This doctoral thesis introduces a strategy based on computational thermodynamics to design C14-type Laves phase alloys optimized for hydrogen storage. The design method employed to investigate the phase stability of alloys of the (Ti, Zr, or Nb)1(V, Cr, Mn, Fe, Co, Ni, Cu, or Zn)2 system, resulted in 440 alloys prone to solidify as C14 Laves phase structure. A thermodynamic model was developed to calculate the PCT diagrams of the C14 Laves phase alloys. It was possible to design compositions with equilibrium pressures in a wide range (10−4 to 105 bar). Based on this design approach, seven alloys with different equilibrium pressures were selected, produced, and experimentally characterized. Three alloys did not require activation procedures: (Ti0.5Zr0.5)1(Mn0.5Cr0.5)2, (Ti0.5Zr0.5)1(Fe0.33Mn0.33Cr0.33)2, and (Ti0.33Zr0.33Nb0.33)1(Mn0.5Cr0.5)2 alloys, and they reached hydrogen storage capacity close to H/M = 1 with fast kinetics. Moreover, the experimental PCIs were compared to the calculated ones. The order of magnitude of the equilibrium pressure for the tested alloys were well predicted by the model. These three compositions presented outstanding reversible hydrogen storage properties. Furthermore, the addition of a small fraction of Ce (0.4 wt.%) was proved to be an efficient strategy to allow activation of the alloys that were not able to be activated by thermal or hydrogenation treatments. The (Ti0.5Zr0.5)1(Fe0.5Mn0.5)2 + Ce alloy reversibly absorbed and desorbed the total amount of hydrogen (H/M = 0.9) at room temperature with excellent cycling stability.