is an MEA polarization curve of stress testing of a Pt-based catalyst that was demonstrated simultaneously with Figure . A clear contrast between the beginning of life (BOL) -the first sweep of the AST, and the end of life (EOL) -the last sweep of the AST could be examined. This shows the performance loss of a catalyst while undergoing accelerated stress testing within just 15 hours due to mass transport loss. Mass transport loss occurs when the rate of mass transport of a species to or from electrodes limits current production. Through AST, mass transport loss is emphasized as it accelerates the speed of the uneven distribution of reactants across the catalyst surface, exacerbating catalyst degradation . From the figure, mass transport loss is more significant in regions with high current density. However, with the performance loss being gradually greater, an apparent increase in mass transport loss down the AST can be observed. This mass transport loss continues to decrease from 3h to 6h; however, the performance of 9h in the high current density region is slightly better than that after 6h, indicating a possible reduced mass transport loss. After 15h, the performance deteriorates even more, having significant kinetic degradation on the catalyst. As such, a prominent trend can be observed as the MSA of the platinum catalyst slowly deteriorates as the time of the AST increases (X. .