Downward Band Bending as an Efficient Strategy to Accelerate Oxygen Exchange Kinetics in Mixed Conducting OxidesRStudies on Different Oriented LSCF Thin Films

Sr segregation, generally observed in Sr-based perovskites,hasbeen found to demonstrate great yet puzzling impacts on oxygen surfaceexchange reaction rates of mixed ionic-electronic conductors(MIECs). In this work, (100)-, (110)- and (111)-oriented La0.6Sr0.4Co0.2Fe0.8O3-& delta; (LSCF) surfaces are first adopted to theoretically and experimentallyinvestigate the effects of Sr segregation, namely, SrCO3, on their catalytic activity toward the oxygen surface exchangereaction. Density functional theory (DFT) calculations show that SrCO3 clusters have very positive effects on LSCF (100) and (111)surfaces and vast negative effects on the LSCF (110) surface, whichmakes the reaction energy barriers change from LSCF(110) < LSCF(111)< LSCF(100) to LSCF(111)-SrCO3 < LSCF(100)-SrCO3 < LSCF(110)-SrCO3. The greatly promoted oxygenexchange kinetics of LSCF (100) and (111) surfaces should arouse fromtheir downward band bending in the presence of SrCO3, whichroots in their relatively higher work functions than that of the SrCO3 cluster and brings forth electron accumulation. Electricalconductivity relaxation (ECR) results verify much-improved oxygensurface exchange rates on the two films. Our findings present an efficientstrategy to accelerate oxygen surface exchange reaction kinetics onMIECs by adopting a second phase to trigger downward band bending.