Electrochemical CO2 Valorization Pathways and Processes toward C2 to C6 Products: Acetylene, Propylene, Butadiene, and Benzene.

CO2 electrolysis on Cu catalysts at near-ambient conditions yields a range of important C1 to C3 products. Despite recent advances, our mechanistic understanding of the CO2 electrolysis reaction network has remained incomplete, with C4 products, and in particular long sought-after aromatic C6 product molecules, still being elusive. Here, we use a real-time capillary DEMS technique to determine the kinetic onset potentials of a wide set of C1-3 CO2 reduction products. Included in our study are rarely reported products, such as propionaldehyde, propylene, and, first, acetylene, C2H2. We then focus on the formation of acetylene, C2H2, and also investigate its alkyne electro-reduction, the C2H2 reduction reaction (C2H2RR). Acetylene electrodimerizes to the C4 compound 1,3-butadiene in a 2e- reduction reaction. It also revealed a potential-dependent electroless Cu-catalyzed ambient-condition [2 + 2 + 2] cycloaddition reaction to C6 benzene. We discuss mechanisms and the significance of the potential-dependent valorizations of acetylene on Cu. We hypothesize a future process concept to valorize CO2 into sustainable C6 e-aromatics.