S 2– ‐Mediated Adsorption Configuration Tuning Enables Selectivity Switching in CO 2 Reduction Over Cu Electrocatalysts

ABSTRACT Product selectivity in the electrochemical CO 2 reduction reaction is strongly governed by the surface adsorption properties of reactant molecules and reaction intermediates. Using oxide‐derived copper as a model electrocatalyst, it is demonstrated that sulfur modification can redirect the CO 2 reduction pathway from multicarbon products to formate by tuning the adsorption configuration of CO 2 . Notably, this selectivity transition is highly sensitive to the concentration of sulfide ions (S 2− ), with a pronounced influence even at a concentration as low as 1 μmol/L. By combining in‐situ spectroscopy characterizations, theoretical calculations of adsorbed CO 2 reduction intermediates, and controlled CO electrolysis experiments, it is revealed that the introduction of S 2− alters the adsorption mode of CO 2 on the Cu surface from C‐site adsorption to O‐site adsorption, thus enabling the observed switch in product selectivity of CO 2 reduction. This work provides a new perspective for understanding and steering the product selectivity of the electrochemical CO 2 reduction reaction by engineering the adsorption configuration of key intermediates.