Nitrite Reduction at Low Overpotentials on N-Doped Carbon: When Metal Single Atoms Become Poisons

We report a nitrogen-doped carbon derived from tetracyanoquinodimethane (TCNQ900) that alone catalyzes nitrite reduction (NO₂^- RR) to NH₃ with an onset potential higher than +0.10 V vs RHE and catalytic activity rivaling state-of-the-art transition-metal catalysts. Contrary to the usual view that carbon supports merely modulate metal sites, we show the reverse: atomically dispersed Cu on TCNQ900 poisons active N-rich motifs, preventing the formation of a tandem catalyst in which NO₃^- is first reduced to NO₂^- by Cu and subsequently to NH₃ by TCNQ900. Molecular analogues confirm that Cu coordination blocks N-rich pockets that drive the NO₂^- RR. In contrast, physically mixing Cu nanoparticles with TCNQ900 restores a true tandem effect: Cu NPs reduce NO₃^- to NO₂^-, while unpoisoned TCNQ900 converts NO₂^- to NH₃, achieving 4-fold higher partial currents. These findings overturn the "noninnocent" support concept and highlight the reciprocal influence of metals on carbon catalysts, providing new designing guidelines and pointing to the potential role of carbon supports as active actors in catalysis.