Direct synthesis of La-Mg-Ni-Co type hydrogen storage alloys from oxide mixtures

(La1 - x Mg x)(2) (Ni0.8Co0.2)(7) (x = 0.125, 0.25, 0.5) alloys were synthesized from the sintered mixture of La2O3 + NiO + CoO + MgO in the molten CaCl2 electrolyte at 750 degrees C and the electrochemical hydrogen storage capacities of the synthesized alloys were measured. Non-hygroscopic LaNiO3 phase formed during sintering (at 1200 degrees C for 2 h) as a result of the reaction of hygroscopic La2O3 with NiO. Another sinter product was Mg0.4Ni0.6O phase. Both mixed oxide sinter products facilitated the La-Ni and Mg-Ni phase formations. X-ray diffraction peaks indicated that the first stable phase appeared in the alloy structure was LaNi5 which formed upon reduction of La2NiO4 phase. Increase in Mg content caused formation of La1.5Mg0.5Ni7 phase in the alloy structure and the presence of this phase improved the hydrogen storage performance of the electrodes. It was observed that (La1 - xMgx)(2) (Ni0.8Co0.2)(7) (x = 0.125, 0.25, 0.5) alloys have promising discharge capacities change between 319 mAh/g and 379 mAh/ g depending on the alloy Mg content. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.