Oxygen Reduction Reaction on Ruddlesden–Popper Phases Studied by Impedance Spectroscopy

Abstract

The oxygen reduction mechanism of Ruddlesden–Popper phases (, Co, Ni) has been investigated by impedance spectroscopy at 500, 600, and under oxygen partial pressure between and 1 atm using both He and Ar as gas carriers. Thick porous electrodes were sprayed on dense and impedance spectra data were collected on symmetrical cells. An equivalent circuit was proposed considering the electrolyte resistances , a Warburg element , and two parallel elements RCpe ( and ). For the three compounds, has been assigned to the oxygen vacancies diffusion in the bulk, the intermediate component, , to oxygen dissociative adsorption in the electrode surface, and the low frequency element, , to oxygen diffusion in the gas phases. In the case of the and compounds, the dependence of Warburg high frequency component suggests a complex process involving both oxygen bulk diffusion and charge transfer. The results of (, Co, Ni) compared with those of perovskite electrodes, allowing us to discuss the effect of the crystal structure on the electrochemical behavior of these layered compounds.