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

Abstract

Sr segregation, generally observed in Sr-based perovskites, has been found to demonstrate great yet puzzling impacts on oxygen surface exchange reaction rates of mixed ionic–electronic conductors (MIECs). In this work, (100)-, (110)- and (111)-oriented La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) surfaces are first adopted to theoretically and experimentally investigate the effects of Sr segregation, namely, SrCO3, on their catalytic activity toward the oxygen surface exchange reaction. 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, which makes 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 oxygen exchange kinetics of LSCF (100) and (111) surfaces should arouse from their downward band bending in the presence of SrCO3, which roots in their relatively higher work functions than that of the SrCO3 cluster and brings forth electron accumulation. Electrical conductivity relaxation (ECR) results verify much-improved oxygen surface exchange rates on the two films. Our findings present an efficient strategy to accelerate oxygen surface exchange reaction kinetics on MIECs by adopting a second phase to trigger downward band bending.

A Superior Catalytic Air Electrode with Temperature-Induced Exsolution toward Protonic Ceramic Cells

“…When constructing the model of 900@NPs, a cluster of SCN is introduced onto the (001) surface of cubic PSCN, with a surface coverage of 25%. The charge density difference (Δρ) (Figure b) shows a charge accumulation located on the interface of SCN and PSCN, which would be beneficial for the adsorption and activation of oxygen gas . The plane-averaged charge density difference (Figure c) demonstrates the evolution of Δρ along the z -axis.…”

“…The charge density difference (Δρ) (Figure 6b) shows a charge accumulation located on the interface of SCN and PSCN, which would be beneficial for the adsorption and activation of oxygen gas. 24 The plane-averaged charge density difference (Figure 6c) demonstrates the evolution of Δρ along the z-axis. It can be seen that Δρ fluctuates obviously near the interface, suggesting an abrupt change of charge density and implying strong interaction between SCN NPs and PSCN.…”