Cyanide-based Covalent Organic Frameworks for Enhanced Overall Photocatalytic Hydrogen Peroxide Production.

Photocatalytic oxygen reduction to produce hydrogen peroxide (H2O2) is a promising route to providing oxidants for various industrial applications. However, the lack of well-designed photocatalysts for efficient overall H2O2 production in pure water has impeded ongoing research and practical thrusts. Here we present a cyanide-based covalent organic framework (TBTN-COFs) combining 2,4,6-trimethylbenzene-1,3,5-tricarbonitrile (TBTN) and benzotrithiophene-2,5,8-tricarbaldehyde (BTT) building blocks with water-affinity and charge-separation. The ultrafast intramolecular electron transfer (<500 fs) and prolonged excited state lifetime (748 ps) can be realized by TBTN-COF, resulting in a hole accumulated BTT and electron-rich TBTN building block. Under one sun, the 11013 µmol h-1 g-1 yield rate of H2O2 can be achieved without any sacrificial agent, outperforming most previous reports. Furthermore, the DFT calculation and in situ DRIFTS spectrums suggesting a Yeager-type absorption of *O2⋅- intermediate in the cyanide active site, which prohibits the formation of superoxide radical and revealing a favored H2O2 production pathway.

Coupling Electron Transfer and Redox Site in Boranil Covalent Organic Framework Toward Boosting Photocatalytic Water Oxidation.

The efficient polymeric semiconducting photocatalyst for solar-driven sluggish kinetics with multielectron transfer oxygen evolution has spurred scientific interest. However, existing photocatalysts limited by π-conjugations, visible-light harvest, and charge transfer often compromise the O2 production rate. Herein, we introduced an alternative strategy involving a boranil functionalized-based fully π-conjugated ordered donor and acceptor (D-A) covalent organic frameworks (Ni-TAPP-COF-BF2 ) photocatalyst. The co-catalyst-free Ni-TAPP-COF-BF2 exhibits an excellent ~11-fold photocatalytic water oxidation rate, reaching 1404 µmol g-1 h-1 under visible light irradiation compared to pristine Ni-TAPP-COF (123 µmol g-1 h-1 ) alone and surpasses to reported organic frameworks counterpart. Both experimental and theoretical results demonstrate that the push/pull mechanism (metalloporphyrin/BF2 ) is responsible for the appropriate light-harvesting properties and extending π-conjugation through chelating BF2 moieties. This strategy benefits in narrowing band structure, improving photo-induced charge separation, and prolonged charge recombination. Further, the lower spin magnetic moment of M-TAPP-COF-BF2 and the closer d-band center of metal sites toward the Fermi level lead to a lower energy barrier for *O intermediate. Reveal the potential of the functionalization strategy and opens up an alternative approach for engineering future photocatalysts in energy conversion applications.