Platinum nanoparticles (Pt NPs) have emerged as important catalysts in various industrial applications, including fuel cells, catalytic converters, and chemical synthesis. However, the long-term performance of Pt NPs can be compromised when exposed to reactive conditions such as the acidic environment in proton-exchange membrane hydrogen fuel cells, potentially leading to a loss of catalytic activity. Oxide species (O * , OH * ) are present at high potentials due to electrochemical oxidation reactions occurring close to 0.8 V. These species are thought to be important site-blockers for the ORR, and oxidized catalysts generally show hindered activity, mainly due to site blocking and altered kinetics. For the ORR oxide saturation is also known to lead to hydrolysis i.e. parasitic, non-electrochemical reactions which might contribute to the high onset potential on platinum-based catalysts. This decline in performance presents challenges for the development of durable and efficient catalysts, emphasizing the need for a better understanding of the complex relationship between reactivity conditions and catalyst performance. Experimental studies on the oxidation of platinum nanoparticles have faced challenges, especially when trying to directly link the oxidation state to the resulting chemical reactivity.