The promoting effect of Sr-doping on the oxygen reduction activity of perovskite cathode

Abstract

A stable cathode with high catalytic activity toward oxygen reduction reaction (ORR) plays a key role in the commercialization of solid oxide fuel cells (SOFCs). The cathode material Ba0.8Sr0.2Co0.7Fe0.2Nb0.1O3-δ is synthesized by solid-state reaction method. The introduction of Sr result in a higher porosity and a lower thermal expansion coefficient. It optimizes the concentration ratio of small polarons and oxygen vacancies. The overall reaction of Ba0.8Sr0.2Co0.7Fe0.2Nb0.1O3-δ cathode is determined by three main ORR processes. The change in rate-limiting step are related to partial pressure of oxygen. The ionization process of oxygen atoms is the main rate-limiting step when PO2 is higher than 0.01 atm. The addition of Sr2+ accelerates the ionization process of oxygen atoms and leads to the acceleration of the whole ORR process. The temperature mainly affects the oxygen transport on the cathode surface and in the cathode bulk. The transfer of oxygen ions to the electrolyte and the ionization of oxygen atoms are accelerated at high temperatures.