To better appreciate the unique overall performance of our CO2-to-CO cell design, we contrast the set of kinetic NiNC-IMI GDE parameters to i) those of the reference NiNC-PANI GDE (Figure ), ii) to the best previously published NiNC GDEs (Figure ) and iii) to state-ofart Ag-based catalyst GDEs (Figure ) (details in Supplementary Table ). The comparison attests to the present electrolyzer cell design as a uniquely favorable combination of performance indicators. First, we recall that although the NiNC-IMI and NiNC-PANI catalysts delivered comparable apparent catalytic activities in the liquid-electrolyte H-cell setup, their MEA current density-FECO efficiency relations at varying catalyst loadings differed sharply. We attribute this to distinctly different final catalyst layer morphologies (Figure and). As a result of this, distinct CO2 transfer kinetics in-plane and across the catalyst layers ensued. Paired with the non-catalytic, acid-base CO2 consumption by catalytically generated OH-into HCO3 -and CO3 2-species inside the cathode (Figure ), complex carbon mass transfer and consumption patterns arise (Figure ). To better understand the carbon consumption mechanisms, we conceptually separate the carbon mass transfer inside the cathode into two. First, there is the in-plane carbon mass transfer to the active sites along the active MEA area, which triggers the catalytic CO2 conversion and the non-catalytic acid-base CO2 consumption. Second, there is the through-plane carbon transfer (via CO 3 2-or HCO 3 -, Figure ). The through-plane carbon transfer leads to a current-and efficiency-dependent gas volume (flow rate) depletion in the cell outlet. Based on this, we can formulate three limiting reaction-transport scenarios associated with mathematical correlations between the applied cell current, Icell, the FECO and FEH2 values, and the electrolyzer exit flow rate (𝑉 ̇𝑂𝑢𝑡 ) (Supplementary Figure ):