Effect of A and B-site cations on surface exchange coefficient for ABO3 perovskite materials

A novel approach, called isothermal isotope exchange (IIE), was applied to varying A- and B-site lanthanum manganites, ferrites, and cobaltites in the perovskite crystal structure in order to extract accurate surface exchange coefficients (k*). Pure electronic conductors revealed temperature dependent isotope exchange, while for mixed ionic and electronic conductors (MIEC) the extent of exchange was independent of temperature. MIEC materials have higher k* values than pure electronic conductors in the temperature range from 500-850 degrees C, demonstrating the importance of both electronic species and oxygen vacancies being present for surface exchange. Strontium doped perovskites exhibited opposite temperature dependencies to parent materials. Some perovskites exhibited an apparent negative activation energy for k*, the behavior of which is explained by a precursor-mediated mechanism for dissociative adsorption. The results have significant implications for the improvement of the oxygen reduction reaction for fuel cells, metal-air batteries, and numerous other energy technologies.