Oxygen Evolution and Reduction Reactions on La_0.8Sr_0.2CoO₃ (001), (110), and (111) Surfaces in an Alkaline Solution

Abstract

The oxygen evolution and reduction properties of La_0.8Sr_0.2CoO₃ are characterized using two-dimensional model electrodes with different reaction planes, synthesized on SrTiO₃ single crystal substrates by pulsed laser deposition. Thin-film X-ray diffraction and reflectivity measurements confirm the epitaxial growth of 29-nm-thick La_0.8Sr_0.2CoO₃ (001), (110), and (111) films on SrTiO₃ (001), (110), and (111) substrates, respectively. Cyclic voltammetry curves in 1-M KOH aqueous solution indicate that the (110) film has the highest activity for oxygen evolution and reduction reactions. An expansion of the La_0.8Sr_0.2CoO₃ lattice is observed after the oxygen reduction process, indicating the formation of oxygen defects, with the highest number of defects being produced in the (110) film. X-ray reflectivity analysis demonstrates the formation of a surface layer on the La_0.8Sr_0.2CoO₃ films during electrochemical cycling due to the decomposition of La_0.8Sr_0.2CoO₃. The surface structure constructed at the electrode/electrolyte interface is a crucial factor influencing oxygen evolution and reduction activity of La_0.8Sr_0.2CoO₃.