Molecular Design of Two-Dimensional Antiaromatic Covalent Organic Frameworks for Solar-Driven Overall Water Splitting

The search for metal-free photocatalysts capable of solar-driven overall water splitting is highly pursued but challenging. Modular synthesis enables the creation of two-dimensional (2D) covalent organic frameworks that possess tunable electronic and optical properties, as well as abundant chemically active functional units that are useful for photocatalysis. Therefore, we employed a molecular design strategy to create 22 antiaromatic 2D COFs by assembling dibenzopentalene (DBP) as linker and 21 molecules as nodes, resulting in four 2D topologies. We studied their potential for solar-driven overall water splitting. The results suggest that all of the 2D COFs exhibit a response to visible light and possess band gaps ranging from 1.21 to 2.29 eV. Particularly, a 2D COF tessellated with DBP and 1,3,5-triazine (TRZN) might facilitate the independent occurrence of the hydrogen and oxygen evolution reactions at distinct active sites under light irradiation. In addition, the photocatalytic overall water splitting using solar energy can be achieved in a 2D COF composed of benzene- and halogen-modified DBP due to the increased oxidation potential. Noteworthy, the solar to hydrogen (STH) efficiencies of the two systems are estimated to be 15.8 and 12.6%, respectively. This study has showcased the capability of antiaromatic COFs in photocatalytic overall water splitting using solar energy.