The impact on Fe-N-C ac�vity from changes in the (micro-) environment from RDE to GDE/PEMFC has been discussed. Local pH is one value which could vary between electrocatalysts and tes�ng condi�ons, and is recognized to influence Fe-N-C ac�vity. Meanwhile, the influence of pH on degrada�on is beginning to receive greater aten�on in modelling reac�on mechanisms and dissolu�on trends. Local pH (at the interface between the working electrode and the bulk of the electrolyte) and its effects has been inves�gated and discussed quite extensively in electrochemical CO 2 reduc�on; however, so far it has garnered limited experimental and theore�cal evidence for ORR. Meanwhile, kine�c modelling work by Zenyuk and Litster found during ORR increased pH along Pt mesopore channels, when devoid of Nafion and instead filled with water. It is worth considering that FeN x ac�ve sites are proposed to be located within micropores, which are expected to be filled with water. Even so, Banham and coworkers' experiments suggest that micropore flooding does not contribute significantly to PEMFC performance decay. Instead, kine�c models of Fe-N-C ac�vity decay under different poten�osta�c condi�ons in PEMFCs have been previously proposed, which has led to some debate. S�ll, to date these kine�c models of Fe-N-C have not factored in pH change and condi�ons in GDEs have not been considered.