Kinetics of CO oxidation and redox cycling of Sr2Fe1.5Mo0.5O6-δ electrode for symmetrical solid state electrochemical devices

Abstract

Resultsof the redox cycling of the Sr2Fe1.5Mo0.5O6-δ electrode in contact with the LaGaO3-based electrolyte at 800°С in air - CO/CO2 - Ar/H2 are presented for the first time. The electrochemical impedance method was used to demonstrate that the electrode polarization resistance at fast gas cycling remained almost unchanged. In the long-term cycling from oxidizing to reducing atmospheres (and vice versa) the polarization resistance equilibrated rapidly (slowly). The kinetics of the CO oxidation in CO/CO2 gas mixtures at 800°С (pO2 ≈ 10−16 – 10−19 atm) near the equilibrium electrode potential was studied. By means of a complex approach to the impedance spectra analysis using the distribution of relaxation times and non-linear least squares methods, it was determined that the CO oxidation is limited by three steps: CO adsorption (CO2 desorption) at the electrode surface, oxygen hetero-exchange and the oxygen ion transport in the electrode bulk. We assume that the charge transfer and the gas diffusion do not limit the CO oxidation reaction on the Sr2Fe1.5Mo0.5O6-δ electrode.