Poly-Amide Modified Copper Foam Electrodes for Enhanced Electrochemical Reduction of Carbon Dioxide

A strategy to modulate the electrocatalytic activity of copper toward CO2 reduction involving adsorption of acrylamide, acrylic acid, and allylamine polymers is presented. Modification of electrodeposited copper foam with poly­(acrylamide) leads to a significant enhancement in faradaic efficiency for ethylene from 13% (unmodified foam) to 26% at −0.96 V vs RHE, whereas methane yield is unaffected. Effects from crystalline phase distribution and copper oxide phases are ruled out as the source of enhancement through XPS and in situ XRD analysis. DFT calculations reveal that poly­(acrylamide) adsorbs on the copper surface via the oxygen atom on the carbonyl groups and enhances ethylene formation by (i) charge donation to the copper surface that activates CO for dimerization, (ii) chemical stabilization of the CO dimer (a key intermediate for C2 products) by hydrogen-bond interactions with the −NH2 group, and (iii) facilitating the adsorption of CO molecules near the polymer, increasing local surface coverage. Poly­(acrylamide) with copper acts as a multipoint binding catalytic system where the interplay between activation and stabilization of intermediates results in enhanced selectivity toward ethylene formation. Modification with poly­(acrylic acid) which has a similar structure to poly­(acrylamide) also shows some enhancement in activity but is unstable, whereas poly­(allylamine) completely suppresses CO2 reduction in favor of the hydrogen evolution reaction.