Understanding the process of carbon corrosion and its impact on performance degradation during simulated start-stop operations for the proton exchange membrane fuel cell

There remains a need for a thorough understanding of the process of carbon corrosion in proton exchange membrane fuel cell and its impact on performance degradation so that appropriate preventive measures against carbon corrosion can be implemented. In this study, we examined the carbon corrosion in detail during simulated start-stop cycles. Using double-layer capacitance as an indicator, we tracked the transformations of electrode structure and surface properties. The impact of carbon corrosion on the performance degradation was analyzed via voltage loss breakdown based on the H2/air polarization curve. Ex-situ characterization techniques were conducted to monitor the change of the surface chemical properties and microstructures of electrode. The results show that carbon corrosion and cell performance degradation proceeded in three stages during simulated startstop cycles. Within 150 cycles (Stage 1), the cell overpotential increased slightly, which was due to the increase in the ohmic and gas diffusion medium mass transfer overpotential rather than the electrochemical area loss. After 600 cycles (Stage 2), significant electrode degradation occurred and electrode thickness was reduced to less than its half. As a result, the cell overpotential increased dramatically (by 35.8% at 0.55 A cm-2), which is mainly attributed to the increase of mass transfer overpotential. Eventually (Stage 3), the electrode structure was stabilized after all the surface defects and amorphous carbon were removed. Among these three stages, Stage 2 is the critical stage that causes the major degradation of cell performance.