Abstract Unrecoverable and recoverable performance degradation is a major issue hindering commercialization of polymer electrolyte membrane fuel cells. The recoverable losses, caused for example by a contaminant adsorption, catalyst flooding, ionomer dehydration, and platinum oxidation, can be reversed, usually following an interruption in the cell operation. In order to elucidate the link between platinum oxidation and recoverable performance loss, three MEAs were characterized in this work. They involved catalysts with different nanoparticle sizes and loadings tested using a combination of the electrochemical impedance spectroscopy, constant-voltage, constant-current and potential controlled techniques, before and after electrocatalyst aging. Experimental results indicate that a decrease in specific activity over time is not affected by nanoparticle size or aging. Nevertheless, linear sweep voltammetry, which is adopted to reduce platinum oxide and as diagnostics for oxide composition, reveals that a change in composition is observed in correlation with catalyst morphology and catalyst aging. The formation of the platinum oxide associated with the peak at 0.61 VRHE in the voltammetry is found to decrease the catalyst's specific activity more than oxides associated with peaks at higher potentials. This indicates that the recoverable performance loss due to the platinum oxide formation depends on the oxide composition.