Direct electrolytic preparation of cerium/nickel hydrogen storage alloy powder in molten salt

The preparation of CeNi 5 by direct electrochemical reduction of mixed powders of cerium oxide (CeO 2) and nickel oxide (NiO) (atomic Ce/Ni ratio, 1:5) in a molten mixture of CaCl 2 and NaCl (mass CaCl 2/NaCl ratio, 7:3) at 820 °C has been studied. The influence of process parameters, such as sintering temperature, cell voltage, and temperature of the molten salt, on the electrolysis process are reported. The current–time plots are shown at constant voltage electrolysis under different conditions. The composition and morphology of the products were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results show that pure CeNi 5 can be prepared by direct electrochemical reduction of mixed CeO 2/NiO pellets sintered at 850–1250 °C in CaCl 2/NaCl melt at a voltage of 2.5 V or higher for 11 h. The product from the electrolysis was in the form of porous pellets and could be readily ground into CeNi 5 alloy powder. At a voltage of 2.5 V or higher, the reduction of the mixed oxide starts from NiO to Ni, followed by that of CeO 2 on the surface of the newly formed Ni to form CeNi 5 alloy. The reduction rate increases with increasing cell voltage and temperature of molten salt.