Polymer-Halogen Pockets Steering *CO Adsorption Configurations for Highly Selective CO2 Electroreduction.

The selective CO2 electroreduction (CO2R) toward specific C2 products represents a critical challenge for practical applicability, requiring precise control over *CO intermediates. Herein, a "polymer-halogen" pocketed Cu catalyst is proposed, wherein the adjustable concentration of Iodide ion (I-) within the pocket enables continuous modulation of *CO adsorption configurations on the Cu, thereby enabling tailored CO2R toward ethylene or ethanol production. A perfluorosulfonic acid (PFSA)-modified CuI catalyst is constructed, where I- is in situ leaching from CuI and subsequently confined by PFSA as an anion shielding layer to form polymer-halogen pockets. By tuning the thickness of PFSA shell, the amount of I- in the pocket can be controlled. The surface-enhanced in situ Raman spectroscopy demonstrates that the coverage of *CO intermediates on Cu surface increases and tends to adsorb at low coordination Cu sites in catalyst granule for dimerization reaction as the I- concentration in the pocket increases. Furthermore, the coordination environment exhibits distinct product selectivity. *CO at medium-coordinated sites favor ethanol production, while those at low-coordinated sites are conducive to ethylene formation. This strategy enables wide modulation of ethylene-to-ethanol ratios from 0.65 to 3.96, achieving peak Faradaic efficiencies (FE) of 60.3 ± 2.1% for ethylene and 48.3 ± 1.3% for ethanol.