Measurement of oxygen exchange kinetics on thin-film La _0.6Sr_0.4CoO_3-δ using nonlinear electrochemical impedance spectroscopy

In order to probe the mechanism of O2 reduction on mixed-conducting oxides, we have measured the nonlinear harmonic impedance response of a dense thin-film electrode of La0.6 Sr0.4 CoO3-δ. By combining a well-defined geometry with detection of small nonlinear harmonics, this approach reveals the nonlinear rate law governing O2 reduction/oxidation. Comparison to various models based on nonequilibrium thermodynamics suggests that O2 reduction on La0.6 Sr0.4 CoO3-δ is limited by dissociative adsorption. To the authors' knowledge, this is the first isolation of the full nonlinear rate law governing O2 exchange on a perovskite oxide.