Electrochemical characterization -The electrode was then initially placed in the TF-RDE setup in an inert gas-saturated electrolyte (0.1 M HClO4) under potential control at 0.05 VRHE using a rotator (Pine technologies). All electrocatalysts have been electrochemically activated (50 cycles between 0.05 and 1.2 VRHE with a scan rate of 300 mV s -1 under a rotation rate of 600 rpm). After the activation, the electrolyte has been exchanged for a fresh one. ORR polarization curves have been measured in an oxygen-saturated electrolyte with rotation at 1600 rpm in the potential window 0.05-1.0 VRHE with a scan rate of 20 mV s -1 . At the end of the ORR polarization curve measurement, the electrolyte was purged with CO under potentiostatic mode (0.05 VRHE) to ensure successful CO adsorption. Afterward, the remaining CO in the electrolyte had been displaced and the electrolyte has been saturated with N2. COelectrooxidation has been performed using the same potential window and scan rate as in ORR, but without rotation and in an N2 saturated electrolyte. Electrochemically active surface area (ECSACO) has been determined by integrating the charge in CO-electrooxidation ("stripping") experiments as described in Ref. . For ORR, after subtraction of background current (due to capacitive currents), kinetic parameters were calculated at 0.9 VRHE. The ohmic resistance of the electrolyte has been determined and compensated for as reported in Ref. . For this work, specific activity (SA) and mass activity (MA) have been determined at 0.95 VRHE. Afterwards, the working electrode was carefully transferred to the HT-DE setup (taking care to not introduce any impurities during the transfer process) and an ADT was performed comprised of trapezoid-wave cycling (various numbers of cycles were applied: 1000/5000/10 000/30 000) at 60 °C 0.1 M HClO4 and at various potential windows (LPL-UPL; LPL = 0.6/0.7 VRHE and UPL = 0.8/0.95 VRHE, where LPL is lower potential limit and UPL is upper potential limit; 0.7 V s -1 , 3 s hold at both LPL and UPL). After the last ADT cycle, the working electrode has been again carefully transferred back to the standard TF-RDE setup and the ORR polarization curve as well as CO-electrooxidation has been measured once again (at RT). . In line with the particle size distributions, the experimental ReCatalyst Pt-Co/C possesses a higher ECSACO than the Umicore benchmark. On the other hand, the two are rather similar in terms of specific activity (SA), which was expected. The difference in ECSACO can presumably be attributed to the different methods of the deposition of Pt NPs. Namely, the deposition of Pt NPs in the case of the experimental ReCatalyst Pt-Co/C has been carried out by double passivation with the galvanic displacement method, which, in contrast to commonly used methods, proved to enable significantly better dispersion, enabling the crystallization of the Pt NPs directly on the carbon support, thus combining the Pt NPs synthesis and deposition steps into a single step. As a consequence of higher ECSACO, the mass activity (MA) of experimental ReCatalyst Pt-Co/C is also higher in comparison to the MA of Umicore benchmark. test (ADT) consists of 30 000 trapezoid-wave potential steps between 0.6 V and 0.95 V with a 3 s hold time at both lower potential limit (LPL) and upper potential limit (UPL) and rise time of ~0.5 s or less, at 80 °C. The goal of such a protocol is to imitate realistic conditions of a PEMFC, as much as possible, regarding the potential range of an automotive drive cycle as well as the waiting time due to traffic conditions (e.g. traffic lights, traffic jams, etc.). Furthermore, it refers to the operational potential range where the metal dissolution is expected to be dominant, especially during trapezoid-wave cycling with potential holds, the impact of the carbon support corrosion to the electrocatalyst performance is supposed to be minimized, but still present. However, it is important to emphasize that these tests are intended for the stability tests in the solid-electrolyte MEA, whereas in this work the ADTs have been performed in a modified liquid-electrolyte high-temperature half-cell setup.