Investigation of Gas Diffusion Electrode Systems for the Electrochemical CO2 Conversion

Electrochemical CO2reduction is a promising carbon capture and utilisation technology.Herein, a continuous flow gas diffusion electrode (GDE)-cell configuration has been studied toconvert CO2via electrochemical reduction under atmospheric conditions. To this purpose, Cu-basedelectrocatalysts immobilised on a porous and conductive GDE have been tested. Many systemvariables have been evaluated to find the most promising conditions able to lead to increasedproduction of CO2reduction liquid products, specifically: applied potentials, catalyst loading,Nafion content, KHCO3electrolyte concentration, and the presence of metal oxides, like ZnO or/andAl2O3. In particular, the CO productivity increased at the lowest Nafion content of 15%, leading tosyngas with an H2/CO ratio of ~1. Meanwhile, at the highest Nafion content (45%), C2+productsformation has been increased, and the CO selectivity has been decreased by 80%. The reported resultsrevealed that the liquid crossover through the GDE highly impacts CO2diffusion to the catalystactive sites, thus reducing the CO2conversion efficiency. Through mathematical modelling, it hasbeen confirmed that the increase of the local pH, coupled to the electrode-wetting, promotes theformation of bicarbonate species that deactivate the catalysts surface, hindering the mechanismsfor the C2+liquid products generation. These results want to shine the spotlight on kinetics andtransport limitations, shifting the focus from catalytic activity of materials to other involved factors.