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

## TL;DR

A nitrogen-doped carbon material efficiently reduces nitrite to ammonia, but copper atoms on it can block its activity, while copper nanoparticles work better in tandem.

## Contribution

Shows that metal single atoms can poison carbon catalysts, challenging the traditional view of carbon as a passive support.

## Key findings

- N-doped carbon from TCNQ900 catalyzes nitrite to ammonia with high onset potential.
- Atomically dispersed Cu blocks active N-rich sites, reducing catalytic performance.
- Cu nanoparticles with TCNQ900 enable a tandem effect, boosting partial currents fourfold.

## Abstract

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.