Discharge behaviour of Mg2Ni-type hydrogen-storage alloy electrodes in 6 M KOH solution by electrochemical impedance spectroscopy

The discharge behaviour of Mg2Ni-type hydrogen-storage alloy electrodes in 6 M KOH is investigated by a.c. impedance at room temperature. Comparative measurements are also performed on an LaNi5 electrode. The rate-determining step of the discharge process for the magnesium-based hydrogen-storage alloy electrode is dependent on the alloy composition and depth-of-discharge. The unmodified Mg2Ni has a high charge-transfer and mass-transfer resistance compared with LaNi5. Additions of yttrium and aluminium in Mg2Ni reduced considerably both the resistances and, thereby, produce a remarkable improvement in discharge capacity and rate-dischargeability.