Oxygen Evolution Reaction on La1-xSrxCoO3 Perovskites: A Combined Experimental and Theoretical Study of Their Structural, Electronic, and Electrochemical Properties
The bulk electronic structure, surface composition, conductivity, and electrochemical activity toward the oxygen evolution reaction for the La1-xSrxCoO3 perovskite series (with x = 0, 0.2, 0.4, 0.6, 0.8, 1) are investigated experimentally and theoretically. It is found that Sr substitutions have the effect of straightening the octahedral cage, aligning atoms along the Co-O-Co axis, and increasing the average oxidation state of the Co cations. As a consequence, both the 'ex situ electronic conductivity as well as the activity toward the oxygen evolution reaction are considerably improved. According to density-functional theory calculations, the alignment of the Co-O-Co bonds and the oxidation of the Co cations enhance the overlap between the occupied O 2p valence bands and the unoccupied Co 3d conduction bands, rationalizing the improvement of the conductivity as a function of the Sr fraction. Additionally, a study of the surface properties as a function of the Sr fraction, carried out by X-ray photoelectron spectroscopy (XPS), provides insight both on surface composition and its effects on the OER activity.