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The electrochemical reduction of carbon dioxide (CO2) is a promising technology in light of energy transition and industrial electrification. In this study, two different electrolyzer configurations, flow‐through and flow‐by modes, were analyzed for the production of carbon monoxide to resolve the CO2 mass‐transfer limitation problem at high current densities in gas diffusion electrodes. These two configurations respectively state convective and diffusive flow inside the gas diffusion layer, and their effect was studied on the cathodic performance of the electrolyzer by varying the operating conditions: cathodic potential, electrocatalyst loading, and Nafion content. In flow‐through configuration, a current density of 220 mA/cm2 could be achieved at a faradaic efficiency of 90 %; whereas, in the flow‐by configuration, the current density was at the same faradaic efficiency limited to 140 mA/cm2. However, the flow‐through configuration has a few limitations, such as lower energy efficiency, owing to the higher ohmic drop and the faster deactivation caused by crystallization of electrolyte salts inside the gas diffusion electrode. Therefore, flow‐by mode is currently the most adequate configuration for the long‐term operation of electrolyzers for the reduction of CO2 to CO. This study represents an essential step toward the application of electrolyzers for the electroreduction of CO2.

Bimetallic nanoparticles with tailored size and specific composition have shown promise as stable and selective catalysts for electrochemical reduction of CO 2 (CO 2 R) in batch systems. Yet, limited effort was devoted to understand the effect of ligand coverage and postsynthesis treatments on CO 2 reduction, especially under industrially applicable conditions, such as at high currents (>100 mA/cm 2 ) using gas diffusion electrodes (GDE) and flow reactors. In this work, Cu−Ag core−shell nanoparticles (11 ± 2 nm) were prepared with three different surface modes: (i) capped with oleylamine, (ii) capped with monoisopropylamine, and (iii) surfactant-free with a reducing borohydride agent; Cu− Ag (OAm), Cu−Ag (MIPA), and Cu−Ag (NaBH 4 ), respectively. The ligand exchange and removal was evidenced by infrared spectroscopy (ATR-FTIR) analysis, whereas high-resolution scanning transmission electron microscopy (HAADF-STEM) showed their effect on the interparticle distance and nanoparticle rearrangement. Later on, we developed a process-on-substrate method to track these effects on CO 2 R. Cu−Ag (OAm) gave a lower on-set potential for hydrocarbon production, whereas Cu−Ag (MIPA) and Cu−Ag (NaBH 4 ) promoted syngas production. The electrochemical impedance and surface area analysis on the well-controlled electrodes showed gradual increases in the electrical conductivity and active surface area after each surface treatment. We found that the increasing amount of the triple phase boundaries (the meeting point for the electron−electrolyte−CO 2 reactant) affect the required electrode potential and eventually the C +2e ̅ /C 2e ̅ product ratio. This study highlights the importance of the electron transfer to those active sites affected by the capping agents particularly on larger substrates that are crucial for their industrial application.

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