Highly Selective Reduction of CO₂ to C₂₊ Hydrocarbons at Copper/Polyaniline Interfaces

Electrochemical reduction of carbon dioxide (CO 2 RR) to liquid fuels and valued chemicals is a meaningful approach to decreasing CO 2 emissions and alleviating the energy crisis. In particular, the conversion of CO 2 into multicarbon products is of technological significance. Cu is the only transition metal that is able to catalyze the CO 2 RR to produce C 2+ hydrocarbons, but the catalytic selectivity of pristine Cu is low. Herein we report a facile method to largely enhance the C 2+ selectivity of polycrystalline Cu toward the CO 2 RR. By coating the Cu surface with a 50 nm thick film of polyaniline (PANI), the faradaic efficiency (FE) of C 2+ hydrocarbons was increased from ca. 15% to 60% at −1.1 V RHE in KHCO 3 solutions. When applying the PANI coating onto Cu nanoparticles, the FE of C 2+ hydrocarbons can even reach 80%, with the FE of ethylene over 40%. Such performance remained stable in a test period of 20 h. The superiority of the Cu/PANI interface is not due to the change in the morphology or the electronic properties of the Cu substrate but instead is due to an improvement in the coverage and interaction of the CO intermediate, which facilitates the CO–CO coupling, as revealed by in situ infrared spectroscopy. This study opens an avenue to tuning the catalytic activity and selectivity of Cu toward the CO 2 RR, not through the structure of the catalyst but through the environment above the surface.