Synthesis of La2Ni7 hydrogen storage alloy by the electro-deoxidation technique

La2Ni7 alloy was synthesized in the molten CaCl2 electrolyte by the electro-deoxidation method at 850 °C and the electrochemical hydrogen storage characteristics of the synthesized alloy was observed. Sintering at 1200 °C for 3 h was determined as the optimum condition to have the electrode pellet with enough porosity and mechanical strength. The hydroscopic La2O3 disappeared and the non-hydroscopic La2NiO4 formed during the sintering. The X-ray diffraction peaks indicated that the sinter product La2NiO4 and NiO reduced to LaNi5 and Ni, respectively, within 4 h electro-deoxidation process. The reduction kinetics of LaOCl was relatively slow. This sluggish reduction caused formation of the target La2Ni7 phase only after 6 h electro-deoxidation. The final La2Ni7 alloy structure with small amount of retained LaNi5 was obtained after 10 h electro-deoxidation and this structure did not change up to 25 h. It was observed that the synthesized alloy had maximum discharge capacity of 207 mA h g−1 and the alloy kept more than 90% of its discharge capacity within 20 charge/discharge cycles. According to the gathered EIS data La2Ni7 alloy was estimated to have no considerable surface barrier layer after discharging to hinder the atomic hydrogen diffusion on its surface.