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, in particular long-sought after aromatic C6 product molecules, still being elusive. Here, we use a novel real-time capillary DEMS technique to determine accurate kinetic onset potentials of a wide set of C1-3 CO2 reduction products. Included in our study are rarely and never-before reported reaction products, such as propionaldehyde, propylene, and firstly acetylene. We focus on the formation of acetylene, C2H2, and also investigate its alkyne electro-reduction, the C2H2 reduction reaction (C2H2RR). Acetylene is shown to electro-reduce on Cu catalysts to the C4 compound 1,3-butadiene in a 2e- reduction reaction. In parallel, it revealed a potential-dependent electroless Cu-catalyzed ambient-condition [2+2+2] cycloaddition reaction to C6 benzene. We discuss the mechanistic implications of our experimental kinetic onset potentials and rationalize the potential-dependent valorizations of acetylene on Cu. Finally, we propose a future two-step process concept to valorize captured CO2 into industrially important aromatic C6+ molecules. This process cascade will open up reaction pathways towards sustainable e-aromatics