Reconfiguration of a mixed-valence copper complex during CO₂ electroreduction promotes CO₂-to-C₂H₄ conversion

Understanding the structural changes of high-performance CO₂-to-C₂H₄ catalysts and determining the mode of C-C coupling at active sites during the electrochemical CO₂ reduction reaction (ECO₂RR) are crucial. Molecular catalysts with readily identifiable and uniform active sites permit the elucidation of reaction mechanisms at the molecular level, serving as an optimal platform for investigating the ECO₂RR. Here we report the dynamic structural reconfiguration of a mixed-valence copper-based complex ([Cu^IICl(phen)₂][Cu^ICl₂]; phen = 1,10-phenanthroline) during the ECO₂RR and elucidate the mechanism for its enhanced selectivity towards C₂H₄. The [CuCl(phen)₂][CuCl₂] catalyst exhibits outstanding performance with a maximum faradaic efficiency for C₂H₄ of 47% at -1.2 V vs. RHE. The excellent performance is maintained for at least 4.5 h. During the ECO₂RR, the Cu(II) in the [CuCl(phen)₂]⁺ unit is reduced to Cu(I) and the chlorine atom dissociates at high potential to form an exposed Cu(I) site, possibly resulting in cuprophilic interactions between the two Cu sites. The reconstruction shortens the Cu-Cu distance in the [CuCl(phen)₂][CuCl₂] complex, facilitating the dimerization of *CO and *CHO intermediates to produce C₂H₄. This work presents a fresh perspective on designing ECO₂RR catalysts to produce multi-carbon products through an in situ reconfiguration process.