DISCHARGE BEHAVIOR OF MG2NI-TYPE HYDROGEN-STORAGE ALLOY ELECTRODES IN6 M KOH SOLUTION BY ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY

The discharge behaviour of Mg2Ni-type hydrogen-storage alloy electrode s in 6 M KOH is investigated by a.c. impedance at room temperature. Co mparative measurements are also performed on an LaNi5 electrode. The r ate-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-transf er and mass-transfer resistance compared with LaNi5. Additions of yttr ium and aluminium in Mg2Ni reduced considerably both the resistances a nd, thereby, produce a remarkable improvement in discharge capacity an d rate-dischargeability.