Electrocatalytic CO2 reduction reaction (CO2RR) is a promising strategy to convert CO2 into fuels and building blocks for chemicals, exploiting renewable energy sources. Flow cells using gas diffusion electrodes (GDEs) instead of simple H-cells are required to achieve higher production rates. In a GDE, CO2 diffuses through a porous gas diffusion layer (GDL) and reaches the active sites located in the catalyst layer; the GDL is a crucial component that can affect the performance of the GDE. In this work, we aimed to establish the parameters of the GDL that influence the selectivity toward the different CO2 reduction products in an alkaline flow reactor. We employed commercial Cu nanoparticles as electrocatalyst and selected a range of market-available GDLs: the structure, composition, and type of cracks of the GDL greatly influence the Faradaic Efficiency (FE) of CO, H2, and ethylene (C2H4). With the emphasis on C2H4, it was found that using a crack-free GDE is essential to get higher FEC2H4. At the same time, larger and more abundant cracks are detrimental to C2H4 production and promote hydrogen evolution: for instance, the FEC2H4 varies in the wide range of 13–32%, from the highly cracked to the crack-free GDL. The presence of both sulfur and oxygen in the microporous layer (MPL) of the GDL helps shift the CO2RR selectivity toward CO. The (in)stability of the GDEs at high current density has been correlated with a change in the wetting properties of the GDE and a loss in hydrophobicity.
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