Solid oxide fuel cells (SOFCs) are one of the key technologies on the way to environmentally friendly power generation. Current research activities aim to reduce their operational temperature to intermediate temperatures (400-600 • C) to make their application more feasible. In a recent approach, lanthanum strontium iron oxide (LSF) thin film electrodes, a mixed ionic electronic conducting (MIEC) material, was decorated with tiny amounts of platinum nanoparticles, which led to a significant

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... ovement of the oxygen reduction kinetics. To understand this material combination a precise characterization is of major interest, especially the exact amount of platinum on the surface. As the studied model-type thin film electrode requires a platinum current collector buried beneath the LSF to improve in-plane electron conductivity, a method providing quantitative information as well as sufficient depth resolution is needed. In this work, we further improved the recently presented approach of online laser ablation of solids in liquids (LASIL), which enabled in combination with ICP-MS detection a spatially resolved analysis of the sample composition. Careful optimization of laser parameters and carrier solution led to a depth resolution of 30 nm, which allowed a clear separation of the Pt-signals from the surface decoration and the underlying current collector. The amount of platinum on the surface was determined using calibration with a matrix matched standard and validated by another method. Finally, the imaging capabilities of the proposed online-LASIL approach have been employed to assess the homogeneity of the Pt-decoration, indicating significant variations within the investigated area. Thus, further improvements in the electrochemical properties of the investigated LSF electrodes could be anticipated by fabrication of MIECs with a more homogeneous platinum decoration.