Tailoring Single Co–N₄ Sites Within the Second Coordination Shell for Enhanced Natural Light-Driven Photosynthetic H₂O₂ Production

Rational regulation of the coordination environment of single-atom catalysts (SACs) is a promising yet challenging strategy to enhance their activity. Here, we introduce an O atom into the second coordination shell of Co-N₄ sites via a simple thermal treatment, forming a Co-N₄-ON matrix to boost photosynthetic hydrogen peroxide (H₂O₂) production. This modification significantly alters the electronic structure of the Co site, bringing the d-band center closer to the Fermi energy and elevating the conduction band of Co-N₄-CN to enhance its reducing capacity. Density functional theory (DFT) calculations reveal intensified charge redistribution and a reduced work function in Co-N₄-ON, facilitating O₂ adsorption. Notably, Co-N₄-ON exhibits the lowest O₂ adsorption energy, indicating a stronger interaction between Co-N₄-O and O₂, which is further strengthened by orbital hybridization and charge transfer at their interface, leading to enhanced O₂ activation. The optimized Co-N₄-ON catalyst demonstrates superior O₂ reduction capabilities with the lowest energy barrier during H₂O₂ desorption. Consequently, it achieves a H₂O₂ production rate of 3098.18 μmol g^-1 h^-1 under neutral conditions, which is 2.6 times higher than that of Co-N₄-CN. Moreover, it maintains a production rate of 1967.79 μmol g^-1 h^-1 over 10 h in a continuous flow reactor under natural sunlight and ambient air, highlighting its durability and practicality. This study underscores the crucial role of the second coordination shell in SACs and offers valuable insights into their atomic-level structure-activity relationships, thus contributing to advancements in catalyst design for efficient photosynthetic H₂O₂ production.