Dems Analysis of Electrochemical CO₂ Valorization to C₂–C₆ Products: Acetylene, Propylene, Butadiene & Benzene

Electrochemical CO₂ reduction on Cu catalysts at near-ambient conditions produces a variety of C₁–C₃ products, yet pathways to higher-order molecules remain poorly understood. Using real-time capillary Differential Electrochemical Mass Spectrometry (DEMS), we determined kinetic onset potentials for a broad range of CO₂ reduction products, including rarely reported species such as propionaldehyde, propylene, and, for the first time, acetylene (C₂H₂). We investigated acetylene formation and its subsequent electro-reduction (C₂H₂RR), revealing electrodimerization to 1,3-butadiene via a 2e⁻ pathway. Furthermore, DEMS detected a potential-dependent, electroless Cu-catalyzed [2 + 2 + 2] cycloaddition under ambient conditions, yielding benzene (C₆). These results demonstrate that DEMS can resolve transient intermediates and map valorization pathways from CO₂ to C₂, C₄, and C₆ products, offering new mechanistic insights into alkyne chemistry on Cu. We propose a future process concept to convert CO₂ into sustainable aromatic e-chemicals through targeted intermediate valorization.