We note that the onset of increased Fe concentra�on at ca. 0.73 V RHE on the cathodic scan (Figure ) coincides with the onset of the quinone-hydroquinone redox on the cathodic scan post 8,000 O 2 AST at 80 o C (Figure ), and the second peak onset of increased Fe concentra�on at 0.33 V RHE on the cathodic scan coincides with the onset of the second reversible redox on the cathodic scan. Our observa�ons suggest that the stability of the Fe centre may be intrinsically linked to the chemistry of the surrounding ligands; this no�on is analogous to rela�onships observed by others between the cataly�c ac�vity and the chemistry of the surrounding ligands. We also note an ini�al exponen�al decay in Fe concentra�on (Figure ), which was also observed by Choi et al. for their Fe-N-C catalyst. In our case maximum Fe concentra�on is observed instantaneously upon poten�al cycling in Ar, whereas in the report of Choi et al. maximum Fe concentra�on is reached a�er 2-3 CVs. This could be due to the vastly different catalyst structures between our highly micro-and mesoporous TAP 900@ 57 Fe with high ac�ve site u�liza�on, and the bulky par�cle and predominantly microporous ZIF-8 derived Fe-N-C of Choi et al. Alterna�vely, it could arise from mass transport effects from slow residence �me in Choi et al.'s flow cell design. The structure of unmodified microporous ZIF-8 derived materials will have impeded mass transport, low ac�ve site u�liza�on and therefore delayed detec�on of Fe dissolu�on. Differences in experimental setup and residence �me calibra�on in this work and that of Choi et al. could also contribute to the observed �me difference in Fe concentra�on detec�on.