Intrinsically Conductive and Cu‐Functionalized Polymer‐Composite Membranes as Gas Diffusion Electrodes for CO2 Electroreduction

Abstract We introduced a new class of gas diffusion electrodes (GDEs) with adjustable pore morphology. We fabricated intrinsically conductive polymer‐composite membranes containing carbon filler, enabling a pore structure variation through film casting cum phase separation protocols. We further selectively functionalized specific pore regions of the membranes with Cu by a NaBH 4 ‐facilitated coating strategy. The as‐obtained GDEs can facilitate the electrochemical CO 2 reduction reaction (CO 2 RR) at Cu active sites that are presented inside a defined and electrically conductive pore system. When employing them as free‐standing cathodes in a CO 2 flow electrolyzer, we achieved >70 % Faradaic efficiencies for CO 2 RR products at up to 200 mA/cm 2 . We further demonstrated that deposition of a dense Cu layer on top of the membrane leads to obstruction of the underlying pore openings, inhibiting an excessive wetting of the pore pathways that transport gaseous CO 2 . However, the presentation of Cu inside the pore system of our novel membrane electrodes increased the C 2 H 4 /CO selectivity by a factor of up to 3 compared to Cu presented in the dense layer on top of the membrane. Additionally, we found that gaseous CO 2 could still access Cu in macropores after wetting with electrolyte, while CO 2 RR was completely suppressed in wetted nm‐scale pores.