The mechanism and kinetics of oxygen reduction at thin dense two-dimensional La 0:52 Sr 0:48 Co 0:18 Fe 0:82 O 3Àd (LSCF) electrodes have been investigated in air between 500 and 700°C with electrochemical impedance spectroscopy and steady-state voltammetry. Dense and geometrically well-defined LSCF films with various thicknesses ranging between 16 and 766 nm have been prepared on cerium gadolinium oxide substrates by pulsed laser deposition and structured with photolithography. The current collection was ensured by a porous LSCF layer. A good agreement was found between the experimental data and the impedance of the reaction model calculated with statespace modelling for various electrode potentials and thicknesses. It was evidenced that oxygen adsorption, incorporation into the LSCF and bulk diffusion are ratedetermining while charge transfer at the electrode/electrolyte interface remains at quasi-equilibrium. The 16 and 60 nm thin dense LSCF electrodes appear to be more active towards oxygen reduction than thicker layers and porous films at 600 and 700°C.