Anode aging during PEMFC start-up and shut-down: H₂-air fronts vs voltage cycles

Start-up and shut-down (SUSD) events in proton exchange membrane fuel cells (PEMFCs) are a major source of cathode degradation, causing a loss of electrochemical surface area (ECSA) and carbon corrosion. Our study reveals that also the anode suffers significant damage during SUSD, dominated by the loss of ECSA, induced by potential cycling between ≈0 and ≈1 V upon the passage of H₂/air fronts. Furthermore, we demonstrate the analogy of SUSD-induced anode degradation and that originating from quasi-square wave potential cycling between 0.05 and 1.05 V_RHE. The performance penalties arising from a decrease of the kinetics of the hydrogen oxidation reaction (HOR) and growing H₂ mass-transport resistances are measured via H₂-pump experiments. The thus projected anode voltage losses for low anode Pt loadings (25 μgPt cm⁻²) predict HOR kinetic losses of ≈40 mV at 80ºC and 3 A cm⁻² for aged anode catalyst layers, suggesting that anode degradation by SUSD could be a significant durability issue in future PEMFC systems with ultra-low Pt loadings and with more stable cathode catalyst carbon supports. Moreover, SUSD-induced H₂ mass-transport related overpotentials were identified and attributed to carbon corrosion, indicated by a thinning of the anode catalyst layer upon aging.