摘要: The electrochemical CO2 reduction reaction (CO2RR) offers a promising strategy to produce high-value-added C2+ products. Cu-based catalysts enable C-C coupling but suffer from low C2+ selectivity. Although electronic/structural engineering and cation effects have been widely studied, the role of anions in tuning interfacial water structure and CO2RR pathways remains insufficiently understood. Herein, a series of low-concentration anions were introduced into 1 M KOH to regulate the interfacial water environment over reconstructed CuO. By combining in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and electrochemical impedance spectroscopy, it is revealed that low-concentration anions in 1 M KOH increase the proportion of strong interfacial-water structure in the order of F- > Cl- > Br- > NO3-. Moreover, the moderate strong interfacial-water structure can accelerate *H transfer and promote *CO hydrogenation to *COH, thus favoring asymmetric C-C coupling to produce C2+ products. However, excessively stable interfacial water structure in F--containing electrolyte induces enhanced *H coverage and dominant H2 evolution. A volcano-type relationship is thus observed between C2+ selectivity and the proportion of strongly hydrogen-bonded water. This work emphasizes anion-mediated interfacial water regulation as an effective strategy to enhance C2+ selectivity for CO2RR.