Triadic Sites Drive Tandem CO2-to-Ethanol Conversion by Steering *CO Coverage and *COH Intermediate Formation.

Single metal-coordinated nitrogen-doped carbon (M1-NC) materials hold great promise for electrocatalytic CO2 reduction, yet the precise modulation of their nitrogen configurations to steer ethanol selectivity remains a formidable challenge. Here, we designed Cu1-NC anchored on a carbon support featured with a high pyrrolic-N to pyridinic-N ratio (CuN4/pr-h-NC), which enables an exceptional Faradaic efficiency (FE) of 79.6% for ethanol. Experimental and theoretical studies reveal that pyrrolic-N and pyridinic-N synergize with Cu sites to form novel triadic sites, which regulate the potential-determining step (PDS) from the traditional C-C coupling step to the protonation step of *CO to *COH. Pyrrolic N boosts *CO surface coverage, after which *CO migrates to neighboring pyridinic N sites for hydrogenation to *COH. The resulting *COH readily couples with another *CO at the single Cu site, driving selective ethanol formation. Due to the single-metal-surface-independence of PDS, this mechanism extends to metals traditionally considered inactive for C-C coupling (M = Fe, Co, Ni, Zn). A positive correlation is observed between the ethanol FE and the pyrrolic N/pyridinic N ratio across the series, with ZnN4/pr-h-NC reaching 71.8% at -0.5 V versus RHE. This work establishes an ensemble site engineering strategy to rationally steer CO2 to ethanol pathways for M1-NC electrocatalysts.