Phase stabilities in molten Li/K carbonate of efficient matrix materials for molten carbonate fuel cells: thermodynamic calculations and experimental investigations

In this study, we investigated the thermodynamics and experimental performance of Al, Zr, and Ce species under anode and cathode gas conditions in Li/K carbonate at 650 °C. Among the Al, Zr, and Ce species investigated, we found that lithium aluminate (LiAlO2), lithium zirconate (Li2ZrO3), and cerium/ceria oxide (CeO2) were the most stable materials. Experimentally, we performed immersion tests in molten (Li0.62/K0.38)2CO3 at 650 °C to evaluate the phase and microstructure stabilities of these materials. The γ-LiAlO2 phase transformation, determined using X-ray diffractometry, was dependent on the immersion time. We performed similar measurements for α-LiAlO2, Li2ZrO3, and CeO2 materials in molten Li/K carbonate at 650 °C. From immersion tests, the presence of the α-LiAlO2 phase revealed that phase transformation of γ-LiAlO2 occurs in Li/K carbonate melts under cathode gas atmospheres; in contrast, no phase transformation was evident after immersion of the pure α-LiAlO2 phase in molten carbonate for 5,000 h. Furthermore, we found that Li2ZrO3 and CeO2 were stable phases after immersion in molten carbonate at 650 °C, under both anode and cathode gas atmospheres, for more than 5,000 h.