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Single-atom catalysts templated by metal–organic frameworks for electrochemical nitrogen reduction
Summary:
The authors from University of Science and Technology of China & partners developed Fe₁-N-C single-atom catalysts with atomically dispersed Fe-N₄ sites and hierarchical porosity, achieving 1.56×10⁻¹¹ mol cm⁻² s⁻¹ NH₃ yield and 4.51 % Faradaic efficiency at –0.05 V for electrochemical N₂ reduction.
Background:
1. To replace the energy-intensive Haber–Bosch process, prior SACs for NRR showed low yield and selectivity owing to HER competition and sluggish kinetics.
2. The authors proposed a MOF-templated mixed-ligand strategy to enlarge Fe-distance, suppress aggregation, and create Fe₁-N-C; DFT predicted lowest RDS barrier for Fe.
Research Content:
1. Synthesis: PCN-222(Fe) porphyrinic MOF (Fe-TCPP/H₂-TCPP) pyrolyzed at 800 °C under N₂, etched with HF → Fe₁-N-C; analogues Co₁-N-C & Ni₁-N-C prepared likewise.
2. Characterizations:
1) BET 440 m² g⁻¹; micro- (1.2 nm) & mesopores (3.2 nm).
2) SEM/TEM retain rod morphology; no Fe particles; HAADF-STEM shows isolated Fe atoms.
3) XANES/EXAFS confirm Fe-N₄; XPS N 1s reveals Fe-Nₓ; Raman Iᴅ/Iɢ = 0.93 (high graphitization).
3. Application: Chronoamperometry in 0.1 M HCl under N₂; optimal –0.05 V vs RHE; 5 cycles & 60 h stable; no N₂H₄ detected; ¹⁵N₂ isotope NMR verifies NH₃ source.
4. Mechanism: DFT distal pathway; N₂ adsorption is RDS (ΔG = 1.03 eV) vs 1.30 eV (Co) & 2.29 eV (Ni); Bader charge Fe⁺¹·⁰⁸ suppresses HER, boosting FE.
Outlook:
This work delivers a scalable route to Fe-SACs with record NRR performance, clarifies Fe-N₄ superiority over Co/Ni, and guides future SAC design for green NH₃ synthesis.
Single-atom catalysts templated by metal–organic frameworks for electrochemical nitrogen reduction
Authors: Rui Zhang, Long Jiao, Weijie Yang, Gang Wan, Hai-Long Jiang
DOI: 10.1039/c9ta10206j
Link: https://pubs.rsc.org/en/content/articlelanding/2019/ta/c9ta10206j
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