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 H-2 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 C-2 and C-3 products with a hydrocarbon ratio of C->= 2/CH4 significantly greater than 100 have been observed with several additives. C-13-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 H-2 (similar to 90%) while suppressing methane with certain N-heterocyclic additives.