Thin-film based, low temperature solid oxide fuel cells (LT-SOFCs) have gained much attention due to their capability to reduce the operating temperature (<450 °C) and the ensuing extended life and reduced cost, compared to conventional SOFCs. While highly porous and continuously connected Pt thin films are viewed as an attractive cathode, they are readily apt to sinter and grow into larger, isolated crystallites upon annealing, leading to severe degradation of the cathode performance over time. Here, we address this issue by fabricating a post-encapsulated composite structure, in which gas-permeable and catalytically active solid electrolytes surround porous Pt electrodes. Nanoporous Pt thin films deposited onto a yttria-stabilized ZrO₂ (YSZ) single-crystal substrate are uniformly coated with Sm-doped CeO₂ (SDC) via a simple, cost-effective and scalable coating method known as cathodic electrochemical deposition (CELD). Physical characterization of the nanostructured Pt/SDC composite thin films is done using a range of tools, in this case SEM, TEM, XRD and ICP-MS. AC impedance spectroscopy (ACIS) of symmetric cells (cathode|electrolyte|cathode) with SDC coatings reveals that the enhanced Pt–SDC interactions led to exceptionally high ORR activity and outstanding thermal stability. These observations provide new directions for the achievement of a robust and catalytically active LT-SOFC cathode through modification of the metal surface.