All CO2 ER experiments were performed with a research-grade BioLogic SP-150 potentiostat (BioLogic, USA) with ultra-low-current capability (76 fA current resolution). The electrolyte concentration was 0.01 mol/L, unless otherwise stated. The electrochemical cell was prepared using the set-up developed before for Transmission Electron Microscopy (TEM) electrochemical experiments . In summary both chips were first plasma treated with Argon and the cell was primed with 0.01 mol/L CuSO4 electrolyte at a flow rate of 20 µL/min before inserting into the TEM. Confirmation that the cell had effectively filled with CuSO4 electrolyte was done by observing the cell area under an optical microscope. Once the electrolyte filled the cell entirely, the sample holder was introduced into the TEM. For this step, the electrolyte flow was lowered to 2 µL/min and all electrical connections remained disconnected to ensure that no electrochemical reactions could occur induced by electric fields in the TEM. The electrical connections of the sample holder were then established, while the potentiostat was used to impose 0 nA at the WE and the CE was electrically shorted to the goniometer to prevent adventitious electric currents between the electrodes and the cell cage. The experimental electrochemical potentials were calibrated by comparing the measured CuSO4/Cu electrochemical potential with the standard hydrogen potential for that redox pair (Figure ). The calibrated experimental potentials were identified as SHE'.