## 1 Introduction
Third, dense thin films can allow studying oxygen transport kinetics with no influence of non-kinetic issues, such as particle morphology and connectivity, and porosity and tortuosity typical in porous electrodes. Lastly, the influence of the strain induced by the substrate on the electrocatalytic properties can be investigated. Furthermore, the use of oxide multilayer heterostructures has opened attractive opportunities in the design of new cathode material systems as oxide interfaces can drastically facilitate the ORR kinetics. So far, oxide heterostructure interfaces have been utilized to achieve unique physical and chemical properties such as phase transition [30], electronic reconstruction [31], magnetic domain rearrangement [32], and anomalous oxygen electrocatalysis [33], which are unattainable in the bulk oxides. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **\(\mathbf{D^{*}}\)/cm\({}^{2}\)**-**s\({}^{-1}\) @ 600 \({}^{\circ}\)C** & **\(\mathbf{k^{*}}\)/cm\(\cdot\)s\({}^{-1}\) @ 600 \({}^{\circ}\)C** & **Reference** \\ \hline La\({}_{0.8}\)Sr\({}_{0.2}\)MnO\({}_{3-\delta}\) & \(10^{-17}\) & \(1.12\times 10^{-10}\) & [8] \\ La\({}_{0.5}\)Sr\({}_{0.5}\)MnO\({}_{3-\delta}\) & \(4.22\times 10^{-18}\) & \(10^{-10}\) & [8] \\ La\({}_{0.8}\)Sr\({}_{0.2}\)CoO\({}_{3-\delta}\) & \(1.69\times 10^{-13}\) & \(1.38\times 10^{-8}\) & [8] \\ La\({}_{0.6}\)Sr\({}_{0.4}\)CoO\({}_{3-\delta}\) & \(2.86\times 10^{-9}\) & \(9.09\times 10^{-8}\) & [21] \\ La\({}_{0.5}\)Sr\({}_{0.5}\)CoO\({}_{3-\delta}\) & \(2.51\times 10^{-10}\) & \(3.29\times 10^{-7}\) & [8] \\ La\({}_{0.6}\)Sr\({}_{0.4}\)Co\({}_{0.2}\)Fe\({}_{0.8}\)O\({}_{3-\delta}\) & \(5.83\times 10^{-10}\) & \(2.35\times 10^{-7}\) & [23] \\ Ba\({}_{0.5}\)Sr\({}_{0.5}\)Co\({}_{0.8}\)Fe\({}_{0.2}\)O\({}_{3-\delta}\) & \(1.28\times 10^{-7}\) & \(5.21\times 10^{-5}\) & [24] \\ La\({}_{2}\)NiO\({}_{4+\delta}\) & \(1.35\times 10^{-8}\) & \(1.02\times 10^{-6}\) & [13] \\ La\({}_{1.9}\)Sr\({}_{0.1}\)NiO\({}_{4+\delta}\) & \(4.66\times 10^{-9}\) & \(3.56\times 10^{-8}\) & [13] \\ La\({}_{1.8}\)Sr\({}_{0.2}\)NiO\({}_{4+\delta}\) & \(2.02\times 10^{-10}\) & \(3.51\times 10^{-9}\) & [13] \\ La\({}_{2}\)CuO\({}_{4+\delta}\) & \(2.76\times 10^{-9}\) & \(5.79\times 10^{-7}\) & [11] \\ La\({}_{2}\)NiO\({}_{0.9}\)Co\({}_{0.1}\)O\({}_{4+\delta}\) & \(1.07\times 10^{-8}\) & \(6.52\times 10^{-7}\) & [14] \\ La\({}_{2}\)NiO\({}_{0.9}\)Co\({}_{0.1}\)O\({}_{4+\delta}\) & \(1.34\times 10^{-8}\) & \(7.89\times 10^{-7}\) & [14] \\ La\({}_{2}\)CoO\({}_{4+\delta}\) & \(2.98\times 10^{-8}\) & \(3.91\times 10^{-6}\) & [25] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Oxygen self-diffusion (\(\mathbf{D^{*}}\)) and surface exchange coefficients (\(\mathbf{k^{*}}\)) for solid oxide fuel cells (SOFC) cathode materials. This review aims to provide a synopsis of the major developments and achievements in thin film MIEC cathodes of SOFCs, which can help facilitate the development of intermediate temperature SOFCs. We first discuss the ORR mechanisms on the cathode of SOFCs. We then cover in detail recent advances in ABO\({}_{3}\) and RP oxide thin film cathodes focusing on cobaltites, ferrites, nickelates, and cuprates. The effect of oxide heterostructure interfaces on the ORR kinetics and electrochemical stability is also overviewed. Finally, we present conclusions, perspectives and future developments. As this review deals with mostly epitaxial thin films, we do not focus on the kinetics of oxygen transport. Readers can be referred to relevant comprehensive reviews of oxygen transport in ABO\({}_{3}\) and RP oxide [12; 34; 35].