Exsolution of metal nanoparticles from perovskite-type oxides is a very promising approachto obtain catalysts with superior properties. One particularly interesting property of exsolutioncatalysts is the possibility of electrochemical switching between different activity states. In this work, synchrotron-based in-situ X-ray diffraction experiments on electrochemically polarized La$_0.6$Sr$_0.4$FeO$_3-δ$ thin film electrodes are performed, in order to simultaneously obtain insights into the phase composition and the catalytic activity of the electrode surface. This shows that reversible electrochemical switching between a high andlow activity state is accompanied by a phase change of exsolved particles between metallic $α$-Fe and Fe-oxides. Reintegration of iron into the perovskite lattice is thus not required for obtaining a switchable catalyst, making this process especially interesting for intermediate temperature applications. These measurements also reveal how metallic particles on La$_0.6$Sr$_0.4$FeO$_3-δ$ electrodes affect the H$_2$ oxidation and H$_2$O splitting mechanism and why the particle size plays a minor role.