Influence on the microstructure and hydrogen storage properties of Y–TiFe-based composites with transition metals via mechanical milling

Hydrogen storage using metal hydrides has a promising future due to its advantages of safety, efficiency, cheapness and cleanliness. In this experiment, the Ti_1.08Zr_0.1Y_0.02Fe_0.6Ni_0.3Mn_0.2+10 wt% M (V, Ni and Pd) composite alloy was produced by co-mingling highly active transition metals (V, Ni and Pd) with Ti_1.08Zr_0.1Y_0.02Fe_0.6Ni_0.3Mn_0.2 alloy through ball milling. Then, the activation properties, hydrogen absorption and desorption kinetics, and thermodynamic properties of the alloys were estimated. The results revealed that the catalyst ball milling not only decreased the size of the alloy particles and shortened the diffusion path but also generated new catalytically active centers and increased the diffusion channel of the alloy. The composite Pd ball-milled alloys exhibited superior activation behaviors and hydrogen absorption dynamics, reaching a hydrogen absorption saturation rate of 96.34 % at 100 s, without any activation incubation period at 150 °C, compared to the composite V and Ni ball-milled alloys, which achieved hydrogen absorption saturation rate of 93.34 % and 93.34 % at 100 s, respectively. Nevertheless, the composite V ball-milled alloy showed better hydrogen desorption kinetics and thermodynamic properties. Its hydrogen desorption saturation rate was 97.24 % at 90 °C, and the absolute values of the enthalpy change of its hydrogen absorption and desorption were the smallest of the three composite alloys, at 21.3 kJ‧mol⁻¹ and 23.0 kJ‧mol⁻¹, respectively. Since the electronegativity of V (1.63) was lower than those of Ni (1.91) and Pd (2.20), it is more favourable for reducing the bond energy of the Y–H bond.