Oxygen reduction kinetic enhancements of intermediate-temperature SOFC cathodes with novel Nd0.5Sr0.5CoO3-δ/Nd0.8Sr1.2CoO4±δ heterointerfaces

Solid-oxide fuel cells (SOFCs) are clean and highly efficient electrochemical energy conversion devices and in this study, novel nanolayer-structured cathodes with Nd0.5Sr0.5CoO3-δ/Nd0.8Sr1.2CoO4±δ heterointerfaces for intermediate-temperature SOFCs are developed in which significantly enhanced oxygen reduction reaction (ORR) kinetics are obtained by increasing the interface layers. The electrical surface exchange coefficient (kq) of the resulting sample (NSC214/113-17L) with multilayered heterointerfaces reached 2.917 × 10−7 cm s−1 at 10% oxygen pressure under 500 °C, and was 102–103 times higher than those of the single-phase samples, including NSC113 (1.335 ×10−9 cm s−1) and NSC214 (1.057 ×10−9 cm s−1). Heterointerface characterizations were conducted using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Scanning Transmission Electron Microscopy (STEM), Energy Dispersive Spectrometer (EDS) and Electron Energy Loss Spectroscopy (EELS) and revealed an enrichment of Sr and a decrease in the valence state of cobalt at the interfacial regions. These two factors together induced the generation of oxygen vacancies VO∙∙ and further facilitated ion transportation, as confirmed by density functional theory (DFT) simulations. Our findings provide a novel heterointerface with high activity and offer specific evidence to elucidate the origin of the resulting enhanced ORR kinetics.