Single-atom catalysts (SACs) have
attracted much attention owning to their high catalytic properties.
Herein, yttrium and scandium rare earth SACs are successfully synthesized
on a carbon support (Y1/NC and Sc1/NC). Different
from the well-known M–N4 structure of M–N–C
(M = Fe, Co) catalysts, Sc and Y atoms with a large atomic radius
tend to be anchored to the large-sized carbon defects through six
coordination bonds of nitrogen and carbon. Although Y- and Sc-based
nanomaterials are generally inactive to room-temperature electrochemical
reactions, Y1/NC and Sc1/NC SACs exhibit catalytic
activities to nitrogen reduction reaction and carbon dioxide reduction
reaction due to the modulation of the local electronic structure of
Y/Sc single atoms by N and C coordination. The catalytic functions
of rare earth single atoms not only demonstrate the magical effect
of SACs but also promote the application of rare earth catalysts in
room-temperature electrochemical reactions.
The active sites of Fe–N–C catalysts are nitrogen coordinated iron atoms, FeNx(x = 1–5), that have five possible coordination numbers, corresponding to different ORR activities and PEMFC performances.
N2 electroreduction into NH3 represents an attractive prospect for N2 utilization. Nevertheless, this process suffers from low Faraday efficiency (FE) and yield rate for NH3. In this work, a highly efficient metal‐free catalyst is developed by introducing F atoms into a 3D porous carbon framework (F‐doped carbon) toward N2 electroreduction. At −0.2 V versus reversible hydrogen electrode (RHE), the F‐doped carbon achieves the highest FE of 54.8% for NH3, which is 3.0 times as high as that (18.3%) of pristine carbon frameworks. Notably, at −0.3 V versus RHE, the yield rate of F‐doped carbon for NH3 reaches 197.7 µgNH3 mg−1cat. h−1. Such a value is more than one order of magnitude higher than those of other metal‐free electrocatalysts under the near‐ambient conditions for NH3 product to date. Mechanistic studies reveal that the improved performance in N2 electroreduction for F‐doped carbon originates from the enhanced binding strength of N2 and the facilitated dissociation of N2 into *N2H. F bonding to C atom creates a Lewis acid site due to the different electronegativity between the F and C atoms. As such, the repulsive interaction between the Lewis acid site and proton H suppresses the activity of H2 evolution reaction, thus enhancing the selectivity of N2 electroreduction into NH3.
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