Surface oxygen exchange properties of bismuth oxide-based solid electrolytes and electrode materials

Abstract

The surface oxygen exchange coefficient, k s, has been measured for the solid solution (Bi 2O 3) 0.75(Er 2O 3) 0.25 and (Bi 2O 3) 0.6(Tb 2O 3) 0.4 (abbreviated BE25 and BT40), using gas-phase 18O exchange techniques. The activation enth alpy of k s amounts to ΔE=110 kJ/ mol for BT40 and ΔE=130 kJ/ mol for BE25. The magnitude of k s for the purely ionic conducting BE25 is comparable with values obtained from electrode polarization ( I−V) measurements ( ΔE=140 kJ/mol.) The comparatively high k s values show a ( P O 2 ) n dependence on oxygen pressure with values of n close to 0.5, indicating surface control in the oxygen transport process. Bismuth oxide containing solid solutions show a large activity in the oxygen exchange reaction with the gas phase.