Thermodynamic-guided tailoring of single-atom coordination environments via oxygen chemical potential for efficient C-N coupling

Systematic and precise regulation of coordination environments in single-atom catalysts (SACs) remains challenging due to thermodynamic constraints and kinetic traps. Herein, we report a thermodynamic-guided strategy to tailor the local coordination of Fe single atoms on CoWO4 support by regulating oxygen chemical potential. Via fine-tuning hydrogen partial pressure during pyrolysis, a series of Fe1Ox SACs is synthesized with well-defined Fe-O coordination numbers ranging from 3 to 6. Combining operando characterizations and density functional theory calculations, Fe1O4 is identified as the optimal configuration for hexamethylenetetramine (HMTA) electrosynthesis, which delivers balanced kinetics by moderating free water dissociation for *NH3 generation and strengthening HCHO chemisorption via pronounced Fe 3d-O 2p orbital hybridization near the Fermi level. As a result, the Fe1O4 SAC achieves a HMTA yield of 0.21 mmol h−1 cm−2 with 83.04% Faradaic efficiency at 1.75 V and stability over 200 h in a flow cell. This work establishes a universal thermodynamic approach for precise coordination engineering of single-atom electrocatalysts and provides a general paradigm for kinetically balancing complex multi-intermediate electrocatalytic systems. Precise control of single-atom coordination is hindered by thermodynamic and kinetic constraints. Here, the authors report tuning Fe-O coordination on CoWO4 via oxygen chemical potential control. Optimal Fe1O4 boosts hexamethylenetetramine electrosynthesis with high yield, efficiency and stability.