Effect of annealing on the hydrogen-storage properties of rapidly quenched AB5-type alloys

The effect of annealing on the hydrogen-storage properties of rapidly quenched AB5-type alloys is investigated by electrochemical measurements and X-ray diffraction. Annealing affects discharge capacity, voltage and cycle life. Annealing at an appropriate temperature can give a promising alloy with large capacity, high discharge voltage and long cycle life. Annealing at too high a temperature, such as 800 °C. results in the largest discharge capacity but the worst cycle life. Annealing can also flatten the discharge plateau regions. The striking difference in the phase structure between as-quenched and as-annealed alloys is that new phases occur as the product of annealing at high temperatures such as 600 and 800 °C. These phases are responsible for the deterioration in cycle durability.