Ti _12.5Zr ₂₁V ₁₀Cr _8.5Mn _xCo _1.5Ni _46.5-x AB ₂-type metal hydride alloys for electrochemical storage application: Part 2. Hydrogen storage and electrochemical properties

In Part 2 of this report, the hydrogen gas charging and electrochemical properties of a series of AB ₂-based metal alloys (Ti _12.5Zr ₂₁V ₁₀Cr _8.5Mn _xCo _1.5Ni _46.5-x) designed to have different fractions of Zr-Ni-type secondary phases by varying the Mn/Ni-content were studied to establish correlations of these properties with abundances of the secondary phases. In the gas charging, the general trend of pressure- concentration-temperature slope factor and hysteresis is to diminish with increase in the Zr ₇Ni ₁₀ phase abundance; the trend of reversible hydrogen storage capacity is to increase as the TiNi-derived AB phase abundance increases. As for the electrochemical properties, the number of activation cycles needed to achieve a given percentage of capacity and power decreases with increase in the total amount of secondary phases. Trends of changes in both the total and reversible capacities follow that in AB phase abundance; the evolution of high-rate dischargeability, bulk diffusion, and surface exchange current is similar to that of Zr ₇Ni ₁₀ phase abundance - increase in the beginning and decrease afterward as the Mn-content in the alloy increases. Other properties, such as metal-hydrogen bond strength and maximum gaseous phase storage capacity, are predominately dependent on the alloys' composition, i.e. the Mn/Ni ratio.