Linkage Regulation of β-Ketoamine Covalent Organic Frameworks for Boosting Photocatalytic Overall Water Splitting.

Two dimensional β-ketoamine covalent organic frameworks (2D TP-COFs) are one category of promising metal-free catalysts for photocatalytic overall water splitting (OWS) because of their unusual stability and versatile electronic/optical properties. However, none of the currently reported TP-COFs can accomplish the hydrogen evolution (HER) and oxygen evolution reactions (OER) simultaneously without adding any sacrificial agents and cocatalysts. To address this challenging issue, we rationally designed 23 2D TP-COFs by regulating the linkage groups and comprehensively evaluated their OWS activity by using the first-principles method. First, the electronic band structure calculations at the HSE06 level reveal that the band gap can be reasonably adjusted with values ranging from 1.67-3.16 eV. Among these 23 systems, 10 TP-COFs are realized to match well with both the chemical potentials of H/H and O/HO, which are capable of visible-light-driven OWS from an electronic perspective. Further thermal activity results on OWS demonstrate that only Hep-BDA (heptazine-aniline) and Bpy-4 (bipyrimidinamine) based COFs can satisfy the completely spontaneous of HER and OER under light irradiation and neutral conditions. Importantly, the calculated small exciton binding energies and high carrier mobility for Hep-BDA and Bpy-4 TP-COFs propose they are potentially applied in photocatalytic OWS. We also achieved the theoretical energy conversion efficiency of Hep-BDA can reach as high as 13.01%. Because there are very few successful applications of TP-COFs on OWS, this theoretical work not only offers valuable insights and innovative ideas for the exploration of novel metal-free photocatalysts for OWS but also supplies a direction for the development of new TP-COF derivatives.