Abstract
The perovskite-type proton conductor with the composition of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) has been reported to exhibit the highest proton conductivity among proton conductors. However, cerate-based perovskite materials such as BZCYYb are also known to react with carbon dioxide which causes phase decomposition through the formation of barium carbonate. This is a significant issue because chemical stability is an important property to enable these materials to be utilized for fuel cell applications. In this study, the chemical stability of BZCYYb was investigated in CO2 or CO2 + H2 atmosphere, with or without nickel addition as sintering aid. Some nickel addition is assumed to occur from nickel diffusion in anode-support-type fuel cells. The enhancement of reactivity with carbon dioxide species by adding nickel into BZCYYb was attributed to barium enrichment at grain boundary regions and the formation of an impurity phase of Ba(Y(1−x)Ybx)2NiO5. Moreover, different decomposition reactions depending on the atmosphere have been inferred. In a pure CO2 atmosphere, barium carbonate formation occurred without appearance of the CeO2-based phase, in other words, without decomposition of the perovskite phase. On the other hand, in hydrogen-containing CO2 atmosphere, both the barium carbonate and CeO2-based phase were observed.
