Given the ca. 2 mL of internal volume of tubing between the GDL and the inlet port to the mass spectrometer, the 3 sccm flow rate corresponds to a ca. 40 s delay between the formation of gaseous products at the working electrode and their detection in the mass spectrometer. This delay time is measured as the difference between the start of a CA measurement and the first detection of products in the MS and is used to shift the MS time axis to better match that of the electrochemistry data.