Effect of cobalt addition on the performance of titanium-based hydrogen-storage electrodes

The influence of cobalt addition on the performance of a Ti2Ni hydrogen-storage alloy is examined. The cobalt addition is confirmed by energy dispersive spectroscopy compositional analysis. X-ray diffraction (XRD) results reveal that cobalt partially substitutes the nickel in the Ti2Ni alloy. Charge/discharge cycle measurements show that the specific capacity of Ti2Ni electrodes increases with cobalt addition, reaches a maximum at a cobalt content of 0.67 at.% (Ti2Ni0.98Co0.02), and then falls with further addition. The cycle life of Ti2Ni electrodes increases significantly with cobalt addition. Scanning electron microscopy analysis reveals that cobalt is effective in reducing the disintegration of the Ti2Ni hydrogen-storage alloy powder, while XRD analysis shows that cobalt restricts the oxidation of the Ti2Ni hydrogen-storage alloy. By contrast, the addition of cobalt does not inhibit the formation of the irreversible Ti2NiH0.5 hydride phase.