Precise Modulation of CO2-to-Ethanol Conversion by Fully-Exposed Cun Clusters Induced by Dangling Bonds in Lacunary Polyoxometalate.

The electrochemical CO2 reduction toward ethanol under high current density remains challenging. Herein, WOx-supported fully exposed Cu clusters (FECCs) confined by hollow mesoporous carbon spheres (HMCS) (Cu-WOx@HMCS) are fabricated through the "molecular defect confinement" strategy based on the [PW9O34]9-. The [PW9O34]9- features a tri-lacunary configuration, single-sided dangling bond characteristics, and excellent liquid-phase stability, enabling precise anchoring of the {CuII 6} cluster to realize atomic dispersion at the molecular level, while enabling the controllable construction of the geometric size and electronic structure of FECCs via Cu─O─W bonds during pyrolysis. The Cu-WOx@HMCS executes exceptional performance for CO2-to-ethanol conversion, with Faradaic efficiencies of 80.6% and 75.3% at partial current densities of 322.4 and 677.7 mA cm-2, respectively. Mechanism studies reveal the synergistic regulation: (1) The FECCs display a higher Fermi level compared to Cu nanoparticles, acting as a superior electron donor to promote CO2 adsorption and conversion; moreover, the geometric size effect of FECCs increases the *CO coverage, favoring the C─C coupling. (2) The WOx supplies reactive *H, which favors the hydrogenation of *CO and *CHCOH, steering the asymmetric C─C coupling toward ethanol. This study enables atomic-level design of catalysts by employing polyoxometalates, delivering a crucial method for precisely constructing fully exposed clusters and highly selective CO2RR-to-ethanol.