In a recent study we demonstrated that CO has a mitigating effect on carbon corrosion in HT-PEFCs during simulated start/stop cycling. In this study we extend our investigations regarding this phenomenon. At first, a parameter study was carried out in which the temperature, the water partial pressure, the gas flow rate and the CO partial pressure were varied and their individual influence on carbon corrosion examined. Subsequently, a detailed comparison between start/stop cycling with and without CO in the fuel gas was performed (rapid aging study). This comparison includes real-time carbon corrosion detection via a CO2 sensor and current mapping in 100 segments. In addition, the electrochemically active surface area (ECSA) was measured in spatially resolved manner alongside with polarization curves, characterizing the fuel cell prior and after the simulated start/stop cycling. The results show how CO is mitigating the degradation of the HT-PEFC cathode on a local level. Moreover it was demonstrated that CO in the anodic fuel gas can increase the life-time of HT-PEFCs. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.