Advances in materials design in solid-state energy devices have opened up unprecedented opportunities for development in recent years. This work focuses on understanding, controlling and optimising the mechanism of oxygen reduction reactions (ORR) in complex transition metal oxides, in particular La0.6Sr0.4CoO3-δ (LSC) thin films grown at different substrate temperatures by Pulsed Laser Deposition (PLD). We investigated the surface to bulk elemental distribution of the films with low-energy ion scattering spectroscopy and aimed to correlate it with the electrochemical activity and stability of the films.[1] Although the initial ORR activity of the film grown at high substrate temperature was better than the one grown at low substrate temperature, interestingly, it showed 2-times higher degradation rate in the long-term electrochemical tests. The better stability of the film grown at low substrate temperature is attributed to the segregation of Sr into protruding particles. In this way, Co content reached stoichiometry in the remaining surface. This study emphasizes the influence of processing temperature and post thermal treatments on the electrochemical activity and stability of the PLD films. [1] Celikbilek, O., Cavallaro, A., Kerherve, G., Fearn, S., Chaix-Pluchery, O., Aguadero, A., Kilner, J. A., Skinner, S. J. 2020, “Surface Restructuring of Thin-Film Electrodes Based on Thermal History and Its Significance for the Catalytic Activity and Stability at the Gas/Solid and Solid/Solid Interfaces,” ACS Appl. Mater. Interfaces, 12, pp. 34388−34401.