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

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. •LSCF and LSCF-MgO are etched to study oxygen exchange kinetics.•The roles of surface topography and chemistry on oxygen exchange are investigated.•Etching removes Sr-excess, exposes B-site cations & increases 200% LSCF-MgO surface.•Etching results in reduced activation energy from 1 eV to 0.4 eV.•Etching enhances oxygen exchange kinetics by an order of magnitude.