Amorphous TiCu-Based Additives for Improving Hydrogen Storage Properties of Magnesium Hydride

Abstract

Magnesium hydride has long been regarded as a promising candidate material for hydrogen and heat storage due to its high hydrogen capacity, reversibility, and low cost. Catalytic doping has been demonstrated as one of the most effective methods to improve hydrogen storage properties of MgH₂. In this study, amorphous Ti₄₅Cu₄₁Ni₉Zr₅ and Ti₄₀Cu₄₇Zr₁₀Sn₃ alloys are used as additives for MgH₂. Nanostructured MgH₂ doped with amorphous or crystalline TiCu-based alloys are prepared by using a high-energy mechanochemical synthesis method. Results show that the amorphous TiCu additives provide enhanced catalytic effects compared to crystalline alloys of the same composition. Doping MgH₂ using an amorphous Ti₄₅Cu₄₁Ni₉Zr₅ alloy yielded improved dehydrogenation kinetics compared to using crystalline Ti₄₀Cu₄₇Zr₁₀Sn₃ alloy. The analysis using transmission electron microscopy reveals that there are nanostructured catalytic particles uniformly distributed in the amorphous TiCu-catalyzed MgH₂. The MgH₂ system catalyzed by amorphous TiCu-based alloy shows little degradation during hydrogenation and dehydrogenation cycling at 300 °C. The amorphous TiCu-based catalysts are thermally stable at temperatures up to 360 °C. Heating the amorphous Ti₄₅Cu₄₁Ni₉Zr₅-catalyzed MgH₂ to temperatures above 360 °C led to disproportionation of the catalyst alloy and the formation of MgCu₂ and Ti₂Cu. In addition, PCI analysis of the amorphous Ti₄₅Cu₄₁Ni₉Zr₅-catalyzed MgH₂ shows a slight increase in hydrogen equilibrium pressure, resulting in a reaction enthalpy of -78.7 kJ/mol·H₂ and an entropy of 145.0 J/K·mol·H₂. The entropy calculated from this study is approximately 10 J/K·mol·H₂ higher than values previously reported for undoped and catalyzed Mg-H systems.