For ini�al 20 o C Ar (Figure ), Fe concentra�on above baseline occurs at 0.83 V RHE, iR-free and reaches a maximum concentra�on between 0.64-0.48 V RHE, iR-free . Returning to 0.83 V RHE, iR-free , Fe concentra�on returns to baseline levels. Ini�al 20 o C O 2 current step holds (Figure ) show a lower baseline Fe concentra�on than 20 o C Ar. A fall in Fe concentra�on below baseline levels is observed when increasing current density from -1 to -15 mA cm -2 geo , corresponding to 0.85±0.02 to 0.80±0.01 V RHE, iR- free , respec�vely. When returning anodically to hold at -1 mA cm geo , Fe concentra�on increases and only begins falling back to baseline once returning to hold at -0.05 mA cm geo . Ini�al 75 o C O 2 current hold measurements show a higher baseline Fe concentra�on, with increased Fe concentra�on during holds at -1 to -15 mA cm geo . Fe concentra�on then returns to approximate baseline values during holds at -50 and -100 mA cm geo , corresponding to 0.66±0.04 and 0.62±0.04 V RHE, iR-free , respec�vely. Returning anodically to holds at -15 and -0.6 mA cm geo results in increased Fe concentra�on.