CO₂ Reduction Selective for C_≥2 Products on Polycrystalline Copper with N-Substituted Pyridinium Additives

Electrocatalytic CO₂ reduction to generate multicarbon products is of interest for applications in artificial photosynthetic schemes. This is a particularly attractive goal for CO₂ reduction by copper electrodes, where a broad range of hydrocarbon products can be generated but where selectivity for C-C coupled products relative to CH₄ and H₂ remains an impediment. Herein we report a simple yet highly selective catalytic system for CO₂ reduction to C_≥2 hydrocarbons on a polycrystalline Cu electrode in bicarbonate aqueous solution that uses N-substituted pyridinium additives. Selectivities of 70-80% for C₂ and C₃ products with a hydrocarbon ratio of C_≥2/CH₄ significantly greater than 100 have been observed with several additives. ¹³C-labeling studies verify CO₂ to be the sole carbon source in the C_≥2 hydrocarbons produced. Upon electroreduction, the N-substituted pyridinium additives lead to film deposition on the Cu electrode, identified in one case as the reductive coupling product of N-arylpyridinium. Product selectivity can also be tuned from C_≥2 species to H₂ (∼90%) while suppressing methane with certain N-heterocyclic additives.