Solubilities of NiO and LaNiO_3 in Li/Na eutectic carbonate with rare-earth oxide

摘要

For the commercial application of molten carbonate fuel cells (MCFCs) under high-pressure operation, the problem of Ni shorting should be solved that is closely related to the solubility of cathode material. In order to improve the MCFC cathode stability, effects of the addition of rare-earth metal oxides to the molten carbonates have been quantitatively investigated. Especially, La_2O_3 addition to the molten carbonate significantly decreased the solubility of NiO. Such low solubility of NiO was caused by effects of both the acid-base equilibrium of molten carbonate and the activity of Ni in solid by the formation of complex oxide. Solubilities of LaNiO_3 and Nd_2NiO_4 were also smaller than that of NiO in molten carbonate as the same reason as that of NiO in the molten carbonates with saturated La_2O_3. Based on the data of solubility, a new parameter was proposed to evaluate the solubility of metal ion in molten carbonates. This parameter concerned with the acid-base equilibrium of melts and the activity of solid for the metal oxide. A linear relationship with the measured solubility of metal oxide in molten carbonates was obtained by this parameter. It would be indicated that the parameter is useful for the prediction of metal oxide solubilities in molten carbonates.