The correlative effects of Al and Co on the structure and electrochemical properties of a La-Mg-Ni-based hydrogen storage electrode alloy

Replacing Co in the La-Mg-Ni-based alloys by other cheap materials is an expected goal to reduce the cost of the hydrogen storage alloys. The present study aims to partially substitute Co by Al for the La-Mg-Ni-based hydrogen storage alloys and to get the correlative effects of Al and Co on the structure and electrochemical properties of the alloys. Alloys with composition of La0.7Mg0.3Ni2.75Co0.75-xAlx (x = 0-0.4) were investigated. The results from X-ray diffraction analyses show that all of the alloys mainly consist of a LaNi5 phase and a (La, Mg)Ni3 phase. While LaNi5 phase increases, the (La, Mg)Ni3 phase decreases and the cell volumes of both the phases are enlarged with the increasing substitution of Al for Co. Results of the electrochemical studies indicate that the substitution of Al for Co can enhance the cycle stability of the alloy electrode effectively. The capacity retention after 100 cycles is improved from 45.9% (x = 0) to 82.1% (x = 0.4). However, the maximum capacity and the electrochemical kinetics decrease. The correlative actions of Al and Co on the corrosion and pulverization resistance of the alloys and hence on the cycle stability and electrochemical kinetics of the alloy electrodes were discussed.