High-performance and CO2‑resistant cathode toward electrocatalytic oxygen reduction for solid oxide fuel cells: Doped ceria and SrCo0.7Nb0.1Ni0.2O3-δ composite

Abstract

High oxygen reduction reaction (ORR) activity and sufficient stability are main challenges for high performance cathodes for solid oxide fuel cells (SOFCs) operated at medium temperature (550-700°C). In this study, ionic conducting Sm0.2Ce0.8O2-δ (SDC) are incorporated into perovskite SrCo0.7Nb0.1Ni0.2O3-δ (SCNN) cathode to synergistically improve its ORR activity as well as CO2 tolerance. A series of composite oxide, SCNN-xSDC (x=0, 20, 30, 40 and 50 wt %), were systematically evaluated as candidate cathodes for intermediate temperature SOFCs. Among all cathodes, SCNN-40SDC has the lowest polarization resistance (0.019 Ω cm2), only ∼30% of SCNN (0.066 Ω cm2) at 700°C. Introduction appropriate SDC boosts ORR activity of the composite cathodes, which is owing to enhanced oxygen surface exchange process, as evidenced by higher oxygen surface exchange coefficient (Kchem) and bulk diffusion coefficient (Dchem). Furthermore, the composite cathode shows much enhanced stability under CO2 poisoning, which was ascribed to the suppression of Sr segregation from SrCo0.7Nb0.1Ni0.2O3-δ and alleviated formation of carbonate in condition of SDC addition. Introducing ionic conductor Sm0.2Ce0.8O2-δ to construct a dual-phase cathode is a promising way to improve stability and ORR activity of perovskite oxides for SOFCs.