Promoting Electrocatalytic Activity of a Composite SOFC Cathode La0.8Sr0.2MnO3+δ/Ce0.8Gd0.2O2-δ with Molten Carbonates

The effect of molten carbonates (MCs) on polarization resistance (R-P), a direct measure of oxygen reduction reaction (ORR) activity, of a composite La0.8Sr0.2MnO3+delta/Ce0.8Gd0.2O2-delta (LSM/GDC) solid oxide fuel cell (SOFC) cathode has been systematically investigated in this study over a temperature range of 550-650 degrees C and partial pressure of oxygen (pO(2)) span of 10(-3) similar to 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 R-P(HF)//CPE(HF) component is related to a charge-transfer process, while the low-frequency R-P(LF)//CPE(LF) counterpart is associated with a surface oxygen dissociative adsorption process. Incorporation of an adequate amount of MC significantly reduces R-P(LF) by as much as a factor of 10. Studies on the dependence of R-P 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 CO42- species in the presence of MC. (C) 2013 The Electrochemical Society. All rights reserved.