Oxygen reduction reaction of PrBaCo2−xFexO5+δ compounds as H+-SOFC cathodes: correlation with physical properties

Abstract

PrBaCo_2−xFe_xO_5+δ solid solution is investigated in order to understand the Oxygen Reduction Reaction (ORR) and water formation occurring at the H⁺-SOFC cathode. Careful attention is paid to the study of the physical properties as a function of composition by Thermogravimetry Analysis (TGA), Mössbauer spectroscopy, electrical conductivity and Seebeck coefficient measurements, with the aim to establish the correlation existing with the ORR activity for these Mixed Ionic Electronic Conductors (MIEC). The oxygen diffusion coefficients are determined by Electrical Conductivity Relaxation (ECR) and Isotopic Exchange Depth Profile (IEDP) coupled with Secondary Ion Mass Spectroscopy (SIMS) methods. An electrochemical study is then carried out and shows that the amount of oxygen vacancies is the most influential parameter. Indeed, it allows some hydration of PrBaCo₂O_5+δ oxide and the formation of protonic defects that can induce protonic diffusivity in these MIEC oxides.