To evaluate differences in Fe detec�on and profiles over a longer period, 1 h AST or chronoamperometry (CA) were recorded in 0.1 M HClO 4 (Figure ) or 0.05 M H 2 SO 4 (Figure ). Greater Fe loading-normalized concentra�on is observed over the course of the AST under O 2 than Ar. Fe concentra�on follows a slow decline under O 2 and rapid plateau above baseline under Ar (Figure ). 2.7±0.1% of total Fe is detected during O 2 AST (Figure ), with a charge normalized Fe dissolu�on of 503±3 ng Fe mg FeNC -1 C -1 (Figure ). Meanwhile, half Fe concentra�on is observed under Ar AST (Figure , Figure ); however, normalizing to the total charge passed shows approximately double, with 1022 ng Fe mg FeNC -1 C -1 (Figure ). Preand post-mortem bright-field TEM of these samples shows no forma�on of detectable nanopar�cles under Ar or O 2 (Figure ), indica�ng all Fe demetalla�on leads to dissolu�on at 25 o C, in agreement with former findings of Kumar et al. CA under O 2 at 0.2 V RHE shows a large ini�al spike in Fe concentra�on, which then decays over �me, while CA at 0.6 V RHE shows a smaller spike and lower overall dissolu�on (Figure ). The ini�al spike in 57 Fe concentra�on may be related to double layer charging and rapid change in poten�al. A�er 30 mins, the current density and Fe dissolu�on are equivalent at 0.2 and 0.6 V RHE CA. CA at 0.2 V RHE ends with 4.6±0.4% of total Fe and 686±166 ng Fe mg FeNC -1 C -1 . This is approximately double the values at 0.6 V RHE , with 2.2±0.1% Fe and 358±61 ng Fe mg FeNC -1 C -1 (Figure ). This correlates with the observa�ons from Figure , where greatest Fe dissolu�on occurs around 0.20 V RHE .