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Abstract Proton exchange membrane fuel cells (PEMFCs) are considered a significant player in the hydrogen economy. However, before mass production is possible, significant improvements in durability are necessary. Monitoring the changes in the electrode structure is challenging without a complex measurement apparatus. Precisely, the changes in electrode properties during carbon corrosion (increase in the porosity and electrode collapse) cannot be quantified using conventional electrochemical methods. Here, we report capturing the oxygen diffusivity in the PEMFC cathode catalyst layer using low-frequency electrochemical impedance spectroscopy (0.3-0.01 Hz). The low-frequency arc is fitted with resistance, inductance, and capacitance in parallel to represent the resistance to oxygen supply, inertia to oxygen diffusion, and oxygen storage capacity in the catalyst layer, respectively. Over 600 cycles of accelerated stress test (ASTs) of carbon corrosion, the capacitance increases by 25–45% (0–150 ASTs), indicating an increase in oxygen storage capacity and electrode porosity. Then, (150–600 ASTs) the resistance and inductance increase while the capacitance decreases by 80%, highlighting a decrease of the oxygen diffusivity and storage in the catalyst layer as the electrode collapses, which causes oxygen starvation. Altogether, this low-frequency approach correlates electrochemical impedance measurements with the changes in electrode structure during carbon corrosion.