Understanding the oxygen reduction kinetics on Sr2-xFe1.5Mo0.5O6-δ: Influence of strontium deficiency and correlation with the oxygen isotopic exchange data

Abstract

This paper presents, for the first time, the results of studies of the electrochemical reaction of oxygen reduction on Sr2Fe1.5Mo0.5O6-δ and Sr-deficient Sr1.95Fe1.5Mo0.5O6-δ, as promising electrodes for solid state electrochemical devices, by the electrochemical impedance method with the subsequent interpretation of the data using the concepts outlined in the Adler et al. model. It was established that the oxygen reduction reaction for both electrodes is determined by two relaxation processes associated with oxygen diffusion, oxygen surface exchange, and Knudsen diffusion in the pores of the electrode. Strontium deficiency was found to have a positive effect on the electrochemical activity of the electrodes, enhancing the stage related to oxygen diffusion and surface exchange. Also, for the first time, for Sr2Fe1.5Mo0.5O6-δ, a quantitative correlation for the surface oxygen exchange and diffusion coefficients obtained from the impedance data and by the isotopic exchange method is demonstrated.