Solid oxide cells are a highly promising technology for efficiently converting between electrical and chemical energy in either fuel or electrolysis cell operation. These cells operate at high temperatures of 600-800°C, as they require high oxygen anion mobility. The efficiency and performance of these cells largely depend on the reaction rate of oxygen exchange reactions at the electrode surfaces. These reactions include oxygen anion incorporation and release on the air side and water splitting, H₂ oxidation, or CO₂ splitting on the fuel side. Typical cells use complex porous electrodes with high but unknown active surface area, which is hardly accessible for surface characterisation. In this work, we show the results of combined ambient pressure XPS and electrochemical experiments on model cells with thin film electrodes on which we investigate the material-specific reaction rate and surface chemistry under operation conditions[1]. A fascinating aspect is that surface chemistry strongly deviates from the nominal bulk and changes with time and operation conditions. This talk presents a survey of experiments that show the complex interplay of model cell operation conditions, surface chemistry and surface reaction rate of fuel and air electrode materials. Key results include tracking of cation segregation, sulphur impurity-driven degradation by modification of surface dipoles and the in-situ exsolution of catalytically active Fe nanoparticles.