Intrinsically Conductive and Cu-Functionalized Polymer-Composite Membranes as Gas Diffusion Electrodes for CO Electroreduction.

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-facilitated coating strategy. The as-obtained GDEs can facilitate the electrochemical CO reduction reaction (CORR) 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 flow electrolyzer, we achieved >70 % Faradaic efficiencies for CORR products at up to 200 mA/cm. 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. However, the presentation of Cu inside the pore system of our novel membrane electrodes increased the CH/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 could still access Cu in macropores after wetting with electrolyte, while CORR was completely suppressed in wetted nm-scale pores.