Revisiting Active Site Quantification in CO₂ Electroreduction: The Case for CO Displacement

The selectivity and geometric current density of copper-based electrodes for electrochemical CO₂ reduction (CO₂RR) have been significantly improved, yet research is striving to improve the intrinsic activity of these materials. The accurate quantification of active sites is vital to benchmark the intrinsic activity of the catalysts for electrochemical CO₂ reduction to facilitate activity improvements. Herein, we propose a method to determine the active sites using CO displacement in potassium phosphate buffer at 10 °C. Comparing this method with the electrochemical surface area (ECSA), measured by double-layer capacitance, the most used technique in this field, we demonstrate that CO displacement provides a much more accurate quantification of the number of active sites. By normalizing current density vs the CO displacement active sites, we find electropolished copper foil has the highest intrinsic activity towards CO₂RR. We also reveal there is a clear relationship between surface roughness and chained products.