The electrochemically active surface area (ECSA) loss of the cathode electrode remains a critical issue for proton exchange membrane (PEM) fuel cell durability in zero-emission transportation and stationary power applications. Here, cathode catalyst (Pt) degradation in fuel cells was systematically examined through eight square wave voltage cycling accelerated stress tests in H2/air atmosphere, with varying lower potential limits (LPL) (0.6 and 0.8 V) and dwell times (3 and 10 s). ECSA loss was measured via cyclic voltammetry at the beginning of life and regular cycle intervals. The changes in the catalyst layer structural properties, including Pt particle size distribution and spatial re-distribution was visualized by electron microscopy. It was found that LPL had the greatest impact on ECSA loss due to different rate of oxide removal at various LPLs. Subsequently, longer dwell times at the upper potential limit (UPL) exhibited the most degradation through the anodic dissolution of Pt at high potentials. This was followed by ASTs with longer dwell times at LPL due to slower oxide removal rate at LPL of 0.8 V and enhanced Pt ion mobility for ASTs with prolonged dwell time at LPL of 0.6 V, which was confirmed by observing higher rate of Ostwald ripening and Pt loss into the membrane. These findings could help to better understand the complex underlying mechanisms of Pt degradation in PEMFCs.