Electroreduction of carbon dioxide (CO₂) at oxalate and polypyrrole modified copper surfaces

The electrochemical conversion of CO₂ into useful chemicals remains an active area of investigation, especially towards higher order C₂ and C₃ products such as ethylene, ethanol and n-propanol. Herein, we demonstrate that oxalate modified copper surfaces on porous gas-diffusion electrodes (GDEs) can be used to modify the selectivity of the electrochemical CO₂ reduction reaction (eCO₂RR) towards higher order chemicals using a flow-type electrochemical cell at near-neutral pH and industrially viable current densities. These multi-layer composite cathodes consisting of a Teflon substrate, coated with copper, and then modified with copper oxalate exhibit up to 79% selectivity to C₂₊ products at varying current densities ranging from 50 up to 250 mA cm^-2, representing a shift in electrocatalytic behavior as compared to the pristine copper/Teflon cathode. The oxalate modified copper surface enables further modification with a conductive polymer such as polypyrrole, tunable to varying thicknesses, demonstrating the feasibility of performing oxidative electropolymerization on copper-based GDEs and subsequently using them for the eCO₂RR. We also investigate the changes occurring in these electrodes with respect to particle/grain size, morphology and surface chemistry using SEM, XRD and XPS.