Synthesis of La2(Ni1-xCox)7 (x = 0.05, 0.1, 0.2) Hydrogen Storage Alloys by the Electro-Deoxidation Technique

Abstract

La2(Ni1-xCox)7 (x = 0.05, 0.1, 0.2) alloys were synthesized directly from sintered mixture of La2O3 + NiO + CoO in the molten CaCl2 electrolyte by the electro-deoxidation method at 850°C and the electrochemical hydrogen storage characteristics of the synthesized alloys were observed. Sintering (at 1200°C for 3 h) converted the hygroscopic La2O3 (by the reaction with NiO) into the non-hygroscopic LaNiO3, La3Ni2O6.5 and La4Ni3O9 depending on the Co content of the oxide mixture. The X-ray diffraction peaks indicated that La2NiO4 was the main La-Ni-O phase formed as a result of partial reduction or dissociation reaction to initiate the LaNi5 phase formation. The target La2Ni7 phase formed much later than LaNi5 phase probably due to the sluggish reduction of LaOCl. It was observed that La2(Ni1-xCox)7 (x = 0.05, 0.1, 0.2) alloys had promising discharge capacities changed between 227 mA h g−1 (La2(Ni0.95Co0.05)7) and 332 mA h g−1 (La2(Ni0.8Co0.2)7) depending on the alloy Co content. This work clearly indicated that the electro-deoxidation was very effective method in the synthesis of the hydrogen storage materials.