Effect of PolymerVariation in Cu-Polymer CompositeElectrodes on Electrochemical CO₂ Reduction

Cu-polyamine composite electrodes for the CO₂RR were prepared using three different amine-functionalized polymers: poly-l-lysine (PLL), poly-l-histidine (PLH), and poly-l-arginine (PLA). Of the composite electrodes, the Cu-PLL electrode demonstrated the highest selectivity for multicarbon (C₂₊) products, reaching an FE_C2+ of 74.3% at −0.98 V vs a reversible hydrogen electrode in a flow cell. In situ surface-enhanced Raman spectroscopy studies obtained from the composite electrodes show that a higher surface pH is achieved on the Cu-PLL electrode during the CO₂RR. This higher surface pH is a consequence of larger availability of the uncoordinated amine functionalities on the Cu-PLL electrode surface relative to the other composite electrodes, as shown through X-ray photoelectron spectroscopy. These results suggest that the electrochemical behavior of Cu-polymer composite electrodes toward the CO₂RR can be tuned by both the p<i>K</i>_a value associated with the amine functionality in the polymer and the ability of the amine functionality to complex with Cu²⁺.