CVs acquired with 3 voltage cycles at 50 mV s -1 and 20 mV s -1 scan rates from -0.33 to -1.33 V vs RHE (without resistance compensation) are shown in Fig. . The working electrode current density is calculated on a geometric area basis corresponding to the 0.2 cm 2 aperture of the WE fixture. The MS signal (pressure) for H2, CH4, and C2H4 are shown in subsequent panels, along with the ratio of the MS signal from CO2 to the total for C-containing gases, which approximates the pressure-based, single-pass conversion efficiency of the CO2 to hydrocarbon products. While CO is a known prominent reaction product, its MS quantification is hampered by overlap with a CO2 fragment, and the liquid products are not quantified for the CV experiments. We note that additional calibrations are required to fully interpret the MS signal from a time-varying product stream. To quantitatively validate the AutoGDE for CO2 reduction on a Cu GDE, a series of CA experiments were performed, each with a fresh working electrode electrolyte, which was archived for subsequent liquid product analysis. The time series data for the CA experiments is shown in Fig. . The time integral over each 10 min CA experiment was used to quantify the total electrochemical charge and partial current densities for each quantified product, as shown in Fig. , which shows the approximately reproduced values for the electrochemical and partial current densities at 3 CA potentials. We note that in some experiments at applied bias < -2 V vs RHE, the CA experiment appears unstable, which we attribute to degradation of the GDE via extended operation at current densities in excess of 50 mA cm -2 . Fig. Chronoamperometry results for a sequence of 10 min experiments with the same GDE sample and fresh electrolyte. The time series data in Fig. is averaged to provide the total and current partial densities for the electrochemistry and gaseous products (quantified using the same MS channels as Fig. ). The liquid products are analyzed with off-line GC and HPLC characterization of the electrolyte from each CA measurement. A second GDE sample was measured on a different day at 3 of the CA potentials, showing reproduction of the potential-dependent product distribution.