Experiments for electrochemical CO reduction reaction (CORR) were conducted with a commercially available microchip-based electrochemistry-mass spectrometry (EC-MS) setup (SpectroInlets ApS, Denmark) with a stagnant thin-layer cell (EC-MS cell, Figure ). The EC-MS cell configuration enables gaseous and volatile liquid analytes to be detected and recorded by the quadrupole mass spectrometer on a sub-second time scale. More details regarding the EC-MS setup and cell configuration can be found in reference .