A Cobalt-Free Multi-Phase Nanocomposite as Near-Ideal Cathode of Intermediate-Temperature Solid Oxide Fuel Cells Developed by Smart Self-Assembly

An ideal solid oxide fuel cell (SOFC) cathode should meet multiple requirements, i.e., high activity for oxygen reduction reaction (ORR), good conductivity, favorable stability, and sound thermo-mechanical/chemical compatibility with electrolyte, while it is very challenging to achieve all these requirements based on a single-phase material. Herein, a cost-effective multi-phase nanocomposite, facilely synthesized through smart self-assembly at high temperature, is developed as a near-ideal cathode of intermediate-temperature SOFCs, showing high ORR activity (an area-specific resistance of approximate to 0.028 omega cm(2) and a power output of 1208 mW cm(-2) at 650 degrees C), affordable conductivity (21.5 S cm(-1) at 650 degrees C), favorable stability (560 h operation in single cell), excellent chemical compatibility with Sm0.2Ce0.8O1.9 electrolyte, and reduced thermal expansion coefficient (approximate to 16.8 x 10(-6) K-1). Such a nanocomposite (Sr0.9Ce0.1Fe0.8Ni0.2O3-delta) is composed of a single perovskite main phase (77.2 wt%), a Ruddlesden-Popper (RP) second phase (13.3 wt%), and surface-decorated NiO (5.8 wt%) and CeO2 (3.7 wt%) minor phases. The RP phase promotes the oxygen bulk diffusion while NiO and CeO2 nanoparticles facilitate the oxygen surface process and O2- migration from the surface to the main phase, respectively. The strong interaction between four phases in nanodomain creates a synergistic effect, leading to the superior ORR activity.