Effects of Polyaromatic Film Interfaces on Cu Catalysts for Selective Electrochemical CO2 Reduction

Abstract Electrochemical CO2 reduction (CO2RR) offers a sustainable pathway to convert CO2 into energy-dense fuels and value-added chemicals, addressing both climate and energy storage challenges. This study investigates the effect of polyaromatic film (PAF) coatings on Cu-based catalysts with distinct morphologies (cubes, porous spheres, and small nanoparticles) and compositions (ranging from metallic Cu, to Cu2O and CuO). PAF functionalization modulates the competition between CO2RR and HER in a catalyst- and potential-dependent manner, leading to selective enhancement of C2+ products for specific Cu catalyst types and applied potentials. Notably, PAF-coated Cu2O porous spheres (Cu2O-PSph/PAF) achieved a maximum multicarbon faradaic efficiency of 63% at –1.40 V vs RHE while sustaining a total current density of 16 mA·cm–2. Under high-current density (–127 mA·cm–2) flow-cell conditions, Cu2O-PSph/PAF maintained stable activity for over 80 min, whereas the uncoated analogue exhibited a fast decrease of C2+ production, highlighting the stabilizing role of the polymeric layer during operation. In addition, the PAF coating influences catalyst evolution by partially confining soluble Cu+ species, reducing particle fragmentation, and guiding aggregate formation. Overall, these findings demonstrate that PAF functionalization not only enhances CO2RR selectivity but also improves operational stability and directs the morphological evolution of Cu catalysts under catalytic turnover, offering a versatile strategy for high-performance CO2 electroreduction.