Oxygen exchange kinetics of BaGd0.3La0.7Co2O6−δ with exsolved Co3O4 nanoparticles in dry and humid atmospheres

Abstract

The oxygen exchange kinetics of BaGd_0.3La_0.7Co₂O_6−δ were investigated with pulsed isotope exchange (PIE) measurements in dry and humid atmospheres in the temperature range 400–600 °C in 0.005–0.21 bar O₂. Synchrotron X-ray diffraction and scanning transmission electron microscopy (STEM) revealed exsolved Co₃O₄ nanoparticles dispersed on the surfaces that may contribute to the catalytic activity of the material towards the oxygen exchange reactions. The obtained oxygen exchange rate was 4.45 × 10⁻³ mol m⁻² s⁻¹ at 600 °C in 0.21 bar O₂ with an activation energy of 0.76 eV. The rate determining step of the exchange reaction was determined to be dissociative adsorption of oxygen in both dry and humid atmospheres based on the individual rates of dissociative adsorption and incorporation, as well as pO₂ dependencies of the oxygen exchange rate of around 1. The effect of water on the oxygen exchange rate was found to be dependent on the oxygen partial pressure, decreasing the rate at 0.21 bar O₂ and 600 °C by a factor of approx. 2, while increasing the rate at 0.02 bar and 0.005 bar O₂ by a similar amount. In situ thermogravimetric analysis was used to characterise the oxygen non-stoichiometry of the material throughout the oxygen exchange measurements.