Synthesis of La2MgNi9 hydrogen storage alloy in molten salt

Abstract

La2MgNi9 alloy is synthesized directly from the sintered mixture of La2O3 + NiO + MgO in the molten CaCl2 electrolyte by the electro-deoxidation method at 740 °C and the electrochemical hydrogen storage characteristics of the synthesized alloy are observed. Sintering (at 1200 °C for 2 h) converts the hygroscopic La2O3 (by the reaction with NiO) into the non-hygroscopic La2NiO4 and La3Ni2O7 phases. The X-ray diffraction peaks indicate that the electro-deoxidation causes LaOCl, Ni, LaNi5 and even target phase La2MgNi9 to form within 2 h process time. The molten salt synthesis process ends up with the final alloy structure of 79% La2MgNi9 and 21% retained LaNi5. The porous alloy structure (with approximately 31.66 m2g−1 specific surface area) is beneficial for higher hydrogen storage capacity and it is observed that La2MgNi9 alloy has promising discharge capacity which is approximately 280 mAhg−1. This work clearly indicates that the electro-deoxidation is a very effective method in the synthesis of the hydrogen storage materials.