Unveiling the Dynamic Evolution of Single-Atom Co Sites in Covalent Triazine Frameworks for Enhanced H₂O₂ Photosynthesis

Unraveling the structural evolution and mechanism of active sites in single-atom catalysts (SACs) during H2O2 production under operational conditions remains challenging due to the transient and elusive nature of the underlying reaction processes. Herein, we employ operando X-ray absorption spectroscopy and ab initio molecular dynamics simulations to unveil the dynamic reconstruction behavior of the Co single atom-loaded covalent triazine framework (Co-SA/Py-CTF) during photocatalytic H2O2 production. The unique Py-CTF substrate provides reasonable structural flexibility to the single atom Co site. Under light irradiation and O-2 adsorption, single Co atoms are dynamically released from the Py-CTF substrate and then form transient atom-pairs with neighboring Co atoms, serving as the authentic active site. The dynamic shuttling of Co subnanometer domains between single-atoms and atom-pairs facilitates the transition of the O-2 adsorption configurations from Pauling type to Yeager type, resulting in a record photocatalytic H2O2 yield (2898.3 mu molh(-1)g(-1)). These findings provide insightful observations into the dynamic photochemical behavior of SACs and present an fresh paradigm for the design of intelligent "adaptive catalysts".