Hybridization of covalent organic frameworks and photosensitive metal-organic rings: A new strategy for constructing supramolecular Z-scheme heterostructures for ultrahigh photocatalytic hydrogen evolution

The rational design of Z-scheme heterojunction photosystems based on covalent organic frameworks (COFs) is a promising strategy for harnessing solar energy for hydrogen conversion. Herein, a direct Z-scheme single-atom photocatalyst based on COF and metal-organic ring has been constructed through the supramolecular interactions of coral-like COF (S-COF) and photosensitized Pd₂L₂ type metal-organic ring (MAC-FA1). The MAC-FA1/S-COF heterojunction exhibits good light absorption, efficient charge separation and transfer, slow electron-hole recombination, and highly dispersed Pd active sites, enabling an efficient and stable H₂ evolution reaction. The optimized 4% MAC-FA1/S-COF achieves an H₂ evolution rate of 100 mmol g⁻¹ h⁻¹ within 5 h and obtains a total accumulated turn-over number relative to Pd (TON_Pd) of 437,685 within 20 h, far superior to S-COF, MAC-FA1, M-5/S-COF, Pd/S-COF, and M-5/Pd/S-COF, which is one of the highest records among COF-based photocatalysts for solar-driven H₂ evolution. This is the first work to incorporate photosensitized metal-organic rings/cages into porous crystalline COFs to form a supramolecular Z-scheme heterojunction, which has significant potential as a high-performance photocatalyst for solar-driven H₂ production.