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

Abstract

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 C_1–3 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.