Promoting Electrocatalytic Activity of a Composite SOFC Cathode La\u3csub\u3e0.8\u3c/sub\u3eSr\u3csub\u3e0.2\u3c/sub\u3eMnO\u3csub\u3e3+δ\u3c/sub\u3e/Ce\u3csub\u3e0.8\u3c/sub\u3eGd\u3csub\u3e0.2\u3c/sub\u3eO\u3csub\u3e2-δ\u3c/sub\u3e 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 La0.8Sr0.2MnO3+δ/Ce0.8Gd0.2O2-δ (LSM/GDC) solid oxide fuel cell (SOFC) cathode has been systematically investigated in this study over a temperature range of 550–650°C and partial pressure of oxygen (pO2) span of 10−3 ∼ 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 pO2 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 CO2 −4 species in the presence of MC