Molten salt synthesis of La(Ni1−xCox)5 (x = 0, 0.1, 0.2, 0.3) type hydrogen storage alloys

Abstract

La(Ni1−xCox)5 (x = 0, 0.1, 0.2, 0.3) 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 2 h) converted the hygroscopic La2O3 (by the reaction with NiO) into the non-hygroscopic La2NiO4, LaNiO3, La3Ni2O6.5, La3Ni2O6.84 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 to initiate the LaNi5 phase formation. The increase in the Co content of the sample was observed to delay the La2NiO4 formation and thus the reactions initiated by La2NiO4 reduction. LaOCl formed chemically was the last oxygen including phase remained in the alloy before obtaining the final alloy structure. The porous alloy structure was beneficial for higher hydrogen storage capacity and it was observed that La(Ni1−xCox)5 (x = 0, 0.1, 0.2, 0.3) alloys had promising discharge capacities changed between 223 mA h g−1 (LaNi5) and 325 mA h g−1 (La(Ni0.7Co0.3)5). This work clearly indicated that the electro-deoxidation was a very effective method in the synthesis of the hydrogen storage materials.