Substituent-Biased CO2 Reduction on Copper Cathodes Modified with Spaced Organic Structures

CO2 reduction directed by organic moieties on Cu cathodes was studied by adopting a newly developed on-surface modification method. Organic groups compatible with exposed Cu surface atoms were introduced by electrochemically activated Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC). Three different ethylnyl precursors, each containing 1,3,5-phenyl, tertiary amine, and 2,5-pyridyl moieties, were introduced onto a Cu cathode, by reacting with a three-way azide precursor. The structural characterization of modified electrodes revealed that the modification yielded surfaces composed of exposed surface Cu atoms capable of cooperating with the introduced, barely soluble, organic polymer. The presence of an organic layer on the Cu resulted in improved CO2 reduction efficiency over H-2 evolution. The methane/ethylene selectivity was dependent on the kind of moieties used. The proton supplier ability of the modified organic moiety turned out to be involved in the selectivity, as well as with surface copper rearrangement upon anodization. These findings demonstrate that the organic groups at cooperating sites on the surface Cu can offer a powerful tool for selective CO2 reduction.