Structure and electrochemical hydrogen storage properties of Ti₂Ni alloy synthesized by ball milling

Highlights: • The Ti₂Ni alloy activation requires only one cycle of charge and discharge, regardless of the temperature. • By increasing the temperature the capacity loss, undergoes an increase and it is more pronounced for the 60 °C. • A good correlation is found between the evolutions of the different electrochemical parameters according to the temperature. - Abstract: The structure and the electrochemical hydrogen storage properties of amorphous Ti₂Ni alloy synthesized by ball milling and used as an anode in nickel–metal hydride batteries were studied. Nominal Ti₂Ni was synthesized under argon atmosphere at room temperature using a planetary high-energy ball mill. The structural and morphological characterization of the amorphous Ti₂Ni alloy is carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical characterization of the Ti₂Ni electrodes is carried out by the galvanostatic charging and discharging, the constant potential discharge, the open circuit potential and the potentiodynamic polarization techniques. The Ti₂Ni alloy activation requires only one cycle of charge and discharge, regardless of the temperature. The electrochemical discharge capacity of the Ti₂Ni alloy, during the first eight cycles, and at a temperature of 30 °C, remained practically unchanged and a good held cycling is observed. By increasing the temperature, the electrochemical discharge capacity loss after eight cycles undergoes an increase and it is more pronounced for the temperature 60 °C. At 30 °C, the anodic corrosion current density is 1 mA cm⁻² and then it undergoes a rapid drop, remaining substantially constant (0.06 mA cm⁻²) in the range 40–60 °C, before undergoing a slight increase to 70 °C (0.3 mA cm⁻²). This variation is in good agreement with the maximum electrochemical discharge capacity values found for the different temperatures. By increasing the temperature, the difference between the OCP curves corresponding to C/10 and C/30 regimes undergoes significant growth, reaching a maximum value (ΔE_OCV = 10.3 mV) at 60 °C before undergoing a decrease at 70 °C. A good correlation is found between the evolutions of the corrosion current density with the maximum discharge capacity on one hand and on the other hand with the ΔE_OCV, according to the temperature. The effect of temperature on the different electrochemical parameters (I_corr, C_max, ΔE_OCV) and the various correlations found between them allows us to optimize the performance of the battery and provide proper operation under the good experimental conditions.