Application of cathodic polarization can cause significant changes to the oxygen surface exchange activity of SOFC cathode materials. Therefore, we modified our heterogeneous catalyst system to develop a first-of-its-kind novel in-operando O-18 isotope exchange technique to measure surface exchange processes under electrochemical polarization. This system allows oxygen reduction reaction investigations under real operating conditions. The effect of polarization and temperature on the surface exchange of LSM, LSCF, LSC and LSF cathode materials was investigated. Significant differences were observed for oxygen exchange with and without polarization, depending on the type of material. A model was developed for the understanding and analysis of oxygen exchange profiles under in-operando conditions. The acquired data was fitted to this model, using parameters obtained from simple electrochemical measurements. Using this model, the oxygen exchange coefficient of SOFC cathode materials can be predicted as a function of applied potential. These predictions can be used to rationally optimize cathode material composition and structure, and subsequently be used to determine and predict cathode degradation mechanisms. (C) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: [email protected]. All rights reserved.