Research on solar fuels based on azobenzene/g-C3N4 photoinduced isomerization energy storage

Abstract

Solar photothermal chemical fuels collect and store solar energy through molecular structure changes and release the stored energy in the form of heat. Molecular software was used to construct molecular models of azobenzene and azobenzene–graphite-like phase carbon nitride (AZO–g-C₃N₄), and structure optimization and energy calculations were carried out on the models based on density functional theory. The isomerization recovery time of azobenzene is prolonged by grafting g-C₃N₄, and its energy is increased by 0.87–1.50 eV compared with that of the pre-grafting model. Four azobenzene monomers with different structures were experimentally designed to be grafted onto g-C₃N₄ templates to form AZO–g-C₃N₄ hybrid materials. Compared with that of the original azobenzene, the half-life of the grafted g-C₃N₄ increased from 4 h, 6 h, 12 h, and 15 h to 57 h, 82 h, 164 h, and 223 h, respectively; the thermal stability of the grafted AZO–g-C₃N₄ material was improved by 77–171%, and the energy density reached 32.15 Wh kg⁻¹, 39.6 Wh kg⁻¹, 60.3 Wh kg⁻¹, and 75.79 Wh kg⁻¹, respectively, with high thermal storage and release capability. Results show that the use of azobenzene-grafted g-C₃N₄ templates is an effective method to improve the half-life, thermal stability, and energy storage density of solar fuel recovery systems.