Promoting Electrocatalytic Activity of a Composite SOFC Cathode La 0.8 Sr 0.2 MnO 3+δ /Ce 0.8 Gd 0.2 O 2-δ with Molten Carbonates

Abstract

The effect of molten carbonates (MCs) on polarization resistance (Rp), a direct measure of oxygen reduction reaction (ORR) activity, of a composite La 0.8 Sr 0.2 MnO 3+λ /Ce 0.8 Gd 0.2 O 2-λ (LSM/GDC) solid oxide fuel cell (SOFC) cathode has been systematically investigated in this study over a temperature range of 550-650̊C and partial pressure of oxygen (pO 2 )spanof10- 3 ~ 1 atm. It is shown that the LSM/GDC cathode, either in the pristine or MC-modified states, can be generally modeled by two consecutive parallel circuits consisting of a resistance and a constant phase element (CPE). The high-frequency Rp(hf)//CPE(hf) component is related to a charge-transfer process, while the low-frequency Rp(lf)//CPE(lf) counterpart is associated with a surface oxygen dissociative adsorption process. Incorporation of an adequate amount of MC significantly reduces Rp(LF) by as much as a factor of 10. Studies on the dependence of Rp on temperature and pO 2 further reveal that the rate-limiting step of a LSM/GDC cathode has shifted from the original surface oxygen dissociative adsorption to the formation of an intermediate CO 2 species in the presence of MC. © 2013 The Electrochemical Society. All rights reserved.