Cu + -Mediated CO Coordination for Promoting C-C Coupling for CO 2 and CO Electroreduction.

Selective electrochemical upgrading of CO to multicarbon (C) products requires a C-C coupling process, yet the underlying promoting mechanism of widely involved Cu oxidation states remains largely unclear, hindering the subtle design of efficient catalysts. Herein, we unveil the critical role of Cu in promoting C-C coupling via coordination with a CO intermediate during electrochemical CO reduction. We find that, relative to other halogen anions, iodide (I) in HCO electrolytes accelerates the generation of strongly oxidative hydroxyl radicals that accounts for the formation of Cu, which can be dynamically stabilized by I via the formation of CuI. The in situ generated CO intermediate strongly binds to CuI sites, forming nonclassical Cu(CO) complexes, leading to an approximately 3.0-fold increase of C Faradaic efficiency at -0.9 V relative to that of I-free Cu surfaces. Accordingly, a deliberate introduction of CuI into I-containing HCO electrolytes for direct CO electroreduction brings about a 4.3-fold higher C selectivity. This work provides insights into the role of Cu in C-C coupling and the enhanced C selectivity for CO and CO electrochemical reduction.