Surface chemistry and porosity engineering through etching reveal ultrafast oxygen reduction kinetics below 400 °C in B-site exposed (La,Sr)(Co,Fe)O3 thin-films

Abstract

Oxides are critical materials for energy devices like solid oxide cells, catalysts, and membranes. Their performance is often limited by their catalytic activity at reduced temperatures. In this work, a simple etching process with acetic acid at room temperature was used to investigate how oxygen exchange is influenced by surface chemistry and mesoporous structuring in single-crystalline epitaxial (La0.60Sr0.40)0.95(Co0.20Fe0.80)O3. Using low energy ion scattering and electrical measurements, it is shown that increasing the B-site transition metal cation surface exposure (most notably with Fe) leads to strongly reduced activation energy from Ea≈1 eV to Ea ≈0.4 eV for oxygen exchange and an order of magnitude increased oxygen exchange kinetics below 400 °C. Increasing the active area by ~200% via mesoporous structuring leads to increased oxygen reduction rates by the same percentage. Density functional calculations indicate that a B-site exposed surface with high oxygen vacancy concentration can explain the experimental results. The work opens a pathway to tune surfaces and optimize oxygen exchange for energy devices.