XRD on post-mortem GDE AST samples was conducted to try and deduce the type of Fe x O y , however either the lack of crystallinity, small par�cle size and/or low concentra�on meant no sharp peaks rela�ng to Fe par�cles could be iden�fied (Figure ). The peak at 18.0 o is assigned to polytetrafluoroethylene, which arises from the Nafion backbone. It is worth men�oning that pris�ne TAP 900@Fe does not show a graphite peak at ~25.6 o (002), sugges�ng its amorphous or graphenelike structure, with an average of single atomic layers found from previous Raman analysis. Normalized absorp�on and first deriva�ve XANES of fresh TAP 900@Fe powder and GDE ink, plus post Ar and O 2 25 o C protocols, are compared to references of Fe foil, FeO and Fe 2 O 3 in Figure . A posi�ve shi� of center of mass of the pre-edge in TAP 900@Fe ink and a�er Ar and O 2 protocols signifies an increase of oxida�on state, while their decrease in intensity is related to a change in local coordina�on of Fe. TAP 900@Fe GDE ink displays a near iden�cal spectra to post 25 o C O 2 . This suggests changes in Fe coordina�on and oxida�on state between TAP 900@Fe powder and its ink, similar to a recent report by Saveleva et al. for other Fe-N-Cs. Post Ar protocol shows a lower rising edge posi�on indica�ng a lower average Fe oxida�on state, or change in bond length and/or coordina�on change.