Correlation of Structure and Surface Exchange Kinetics on Bismuth-Based Oxides

Thursday, 5 October 2017: 11:00
National Harbor 7 (Gaylord National Resort and Convention Center)
Y. L. Huang (University of Maryland Energy Research Center), C. Pellegrinelli, M. H. Abdul Jabbar, I. Robinson, and E. D. Wachsman (University of Maryland)
High temperature cubic phase bismuth oxide has the highest ionic conductivity because of the highly defective fluorite structure, with near unity ionic transference number. However, bismuth oxide has multiple crystallographic polymorphs at different temperature domains and the conductivity of bismuth oxide can vary by orders of magnitude depending on the phase. Although cubic phase bismuth oxide can be stabilized by doping, doped bismuth oxides, such as erbium stabilized bismuth oxide (ESB), undergo an anion ordering transition near 600 °C, leading to a decrease in ionic conductivity. The phase transition and anion ordering in stabilized bismuth oxides provides a unique opportunity to directly correlate crystal structure, conductivity and surface exchange properties on ionically conducting oxides. Here, gas phase isotopic oxygen exchange was performed on Bi2O3 and ESB as a function of exchange time at different temperatures, to determine the structure effect on surface exchange kinetics. Our results suggest that bismuth-based oxides have intrinsic catalytic activity toward oxygen exchange and the doping of erbium affects the surface exchange rate. The relationship between diffusion coefficient (D) and surface exchange coefficient (k) on bismuth-based oxides is explored and possible rate-limiting steps are proposed.