Nitrogen Coordination Engineering in Co–N ₄ Single-Atom Catalysts: Distinct Roles of Pyridinic and Pyrrolic Coordination in Regulating Reactive Oxygen Species Generation

Single-atom catalysts have emerged as a powerful platform for advanced catalysis, yet the specific roles of nitrogen coordination in modulating reactive oxygen species remain overlooked. Herein, we integrate theoretical calculations with experimental verification to unravel the functionalities of the ubiquitously coexisting pyridine-type (Co–pdN4) and pyrrole-type CoN4 (Co–poN4) configurations. We reveal that Co–pdN4 significantly outperforms Co–poN4 in O3 activation and contaminant abatement. Electronic structure analysis attributes this kinetic dominance to a reduced work function (5.502 eV for Co–pdN4 vs 5.953 eV for Co–poN4) and a lower energy barrier for O–O bond cleavage on Co–pdN4 (0.349 eV) compared to Co–poN4 (0.396 eV), which facilitate interfacial electron transfer from the Fermi level to the O3 LUMO. Furthermore, the strong electron-withdrawing σ-coordination of pyridinic-N contributes to the structural stability of Co–pdN4 against leaching. Most notably, a distinct divergence in ROS generation governed by N-coordination environment is uncovered: electron-deficient Co–pdN4 sites facilitate the formation of key *O and *OO intermediates to drive a •OH-dominated pathway effectively, whereas electron-rich Co–poN4 sites thermodynamically favor the singlet state configuration, preferentially evolving 1O2. This work establishes a structure–performance relationship, providing design guidance for Co–N4 catalysts with tunable reactivity and selectivity through nitrogen coordination engineering.