The durability of proton exchange membrane fuel cells (PEMFCs) heavily relies on the stability of the cathodic platinum-based electrocatalyst during events like hydrogen fuel starvation or start-up and shut-down. Recent research focused on understanding the degradation mechanisms of Pt catalysts, particularly the transient Pt dissolution triggered by potential shifts above the open-circuit potential. Experiments involving model catalyst materials and electrochemical environments have revealed significant insights into Pt oxidation and dissolution processes. A study employing high energy wide-angle X-ray scattering (WAXS) with a stroboscopic measurement strategy has provided new data on nanocatalyst oxidation trends in PEMFCs, challenging current models. The correlation between early Pt oxide phase transitions and overall PEMFC performance was established, and the predicted transient Pt dissolution was confirmed through electrochemical on-line mass spectrometry experiments. The analysis of structural data revealed time constants for oxide phase transitions, highlighting the limitations of current stress test protocols. By shedding light on Pt oxidation in PEMFCs, this study offers valuable insights for improving catalyst stability and developing durable Pt-based electrocatalysts.