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[Display omitted] • Ionic liquid (IL)-adsorbed catalyst changes the morphology of the catalyst layer. • IL adsorption reduces the ORR charge transfer resistance in the electrode. • IL adsorption enhances the stability under the accelerated durability test. A majority of studies focus on developing oxygen reduction reaction (ORR) catalysts and cathode configurations to enhance the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs). In this study, resistance analyses of the membrane electrode assembly (MEA) are conducted to elaborate on the performance and durability improvements induced by the adsorption of [MTBD][beti] ionic liquid (IL) on the commercial PtCo/C catalyst. The morphological changes caused by IL adsorption are observed on micro and macro scales via physicochemical methods. From the half-cell measurement, when the 4 wt% IL was adsorbed, a 15 mV improvement in ORR activity occurred, and as the adsorption amount increased, the activity decreased. The MEA using 8 wt% IL adsorbed catalyst outperforms 1.7 times higher current density at 0.8 V and 40 % lower charge transfer resistance. Distribution of relaxation time resistance analysis reveals that oxygen mass transfer resistance (R mass), ORR charge transfer resistance (R ORR), and proton charge transfer resistance (R proton) decrease due to IL adsorption. During accelerated durability tests, IL 8 % MEA showed a 58 % increase in durability, and a lower degradation of R ORR and R proton encouraged improved durability. The resistance analyses in this study contribute to identifying the factors responsible for the performance and durability enhancement of PEMFC. [ABSTRACT FROM AUTHOR]