It has been previously suggested that O-containing groups on the carbon surface reduce the turnover frequency of Fe-N-Cs by weakening O 2 -binding on FeN x sites. The limited change in XPS O1s spectra between pris�ne and 20 o C O 2 GDE protocol (Figure ) suggests performance degrada�on from 20 o C O 2 protocol (Figure ) is mainly atributed to ac�ve site demetalla�on. Meanwhile, the increase in O1s a�er 75 o C O 2 protocol (Figure ) causes reduc�ons in TOF and FeN x sites' stability and the increased observa�on degrada�on. Reduc�on in TOF occurs due to reac�ve oxygen species catalyzing mild carbon corrosion. The rapid decay in O 2 reduc�on performance (e.g. -50±30 mV at 50 mA cm geo a�er 200 cycle AST in 20 o C O 2 ) and high Fe dissolu�on can be atributed to the high percentage of unstable high spin Fe 3+ N x present (assuming the same type of sites are present between TAP 900@ 57 Fe and TAP 900@Fe). Addi�onally, according to density func�onal theory (DFT) calcula�ons for Fe-N-C, the number and size of graphene sheets affects the Fe dissolu�on poten�al. Previous Raman analysis of TAP 900 determined an atomically thin carbon structure, which therefore leads itself to possess less stable FeN x sites.