Electronic Activation of Cathode Superlattices at Elevated Temperatures - Source of Markedly Accelerated Oxygen Reduction Kinetics

摘要

Solid-oxide fuel cells are an attractive energy conversion technology for clean electric power production. To render them more affordable, discovery of new cathode materials with high reactivity to oxygen reduction reaction (ORR) at temperatures below 700 ℃ is needed. Recent studies have demonstrated that La_(0.8)Sr(0.2)CoO_3/(La(0.5)Sr_(0.5))_2CoO_4 (LSC_(113/214)) hetero-interfaces exhibit orders of magnitude faster ORR kinetics compared with either single phase at 500 ℃. To obtain a microscopic level understanding and control of such unusual enhancement, we implemented a novel combination of in situ scanning tunneling spectroscopy and focused ion beam milling to probe the local electronic structure at nanometer resolution in model multilayer superlattices. At 200-300 ℃, the LSC_(214) layers are electronically activated through an interfa-cial coupling with LSC_(113). Such electronic activation is expected to facilitate charge transfer to oxygen, and concurrent with the anisotropicaliy fast oxygen incorporation on LSC_(214), quantitatively explains the vastly accelerated ORR kinetics near the LSC_(113/214) interface. Our results contribute to an improved understanding of oxide hetero-interfaces at elevated temperatures and identify electronically coupled oxide structures as the basis of novel cathodes with exceptional performance.