Polymer-tethered pyridine tunes activities of the two distinct CO₂ electroreduction sites on Cu

CO₂ electroreduction (CO₂RR) to multi-carbon products on Cu was found to occur via a two-site mode: one site is more active for CO₂-to-CO conversion, and the other is primarily responsible for CO reduction. However, it remains unclear whether the activities of these two sites can be modulated independently. Here, we show that polyvinylpyridine, a pyridine-functionalized polymer, preferentially enhances the activity toward multi-carbon products at the CO₂-to-CO site by a factor of 3 while reducing that of the CO reduction site. Poly-4-vinylpyridine-(P4VP)-modified Cu₂O-derived Cu (OD-Cu) increases the multi-carbon product Faradaic efficiency by a factor of 1.3 to 3 across a current density range of 60 to 260 mA cm^-2. Moreover, the CO reduction reaction (CORR) activity decreases by up to 40% in the same range when P4VP is introduced. Isotopic labeling, in-situ Raman spectroscopy, contact angle tests, and theoretical calculations reveal that this phenomenon arises from CO₂ enrichment, increased hydrophilicity, and Cu surface charge redistribution in the presence of polyvinylpyridine. These findings demonstrate the potential to independently control CO₂ reduction at different active sites.