Structure and electrochemical hydrogen storage properties of Ti ₂Ni alloys

Ti₂Ni alloy has a high theoretical hydrogen storage capacity of about 500 mAh/g, however,only about 55% of the capacity of a Ti₂Ni crystalline alloy can be discharged. Moreover,severe capacity loss occurs during charge and discharge cycles. Mechanical milling (MM) lias been used to treat the crystalline Ti₂Ni alloy. MM contributes to a decrease in grain size and the formation and increase of the amorphous phase by increasing the milling time, resulting in improvements of the antipulverization ability and cycle life after the milling. The result of linear polarization indicates that the exchange current density increases first and then decreases. The amorphous phase is beneficial to hydrogen diffusion according to the result of potential-step measurement. The electrochemical properties of Ti₂Ni alloy are significantly improved by the non-equilibrium processing technology. The crystalline behavior of the amorphous alloy was also studied,relative to a multi-stage crystallization mode,using X-ray diffraction,differential scanning calorimetry, and electron diffraction. X-Ray photoelectron spectroscopy was performed to analyze the surface structure of the alloys. The alloy that was heat-treated at 693 K,with a non-equilibrium bulk structure and a protective surface layer,has a high discharge capacity and good cycling stability. The issue of severe capacity loss of Ti₂Ni-based alloys, which has caused problems for many years, has been significantly improved.