Photocharging Storage Capacity of C-rich Polymeric Carbon Nitrides Enhanced by TiO2

The light-induced accumulation of long-lived trapped electrons within the conjugated heptazine backbone enables polymeric carbon nitrides the dual ability of light absorption and charge storage. However, the photocharge storage capacity of C-rich polymeric carbon nitride(CPCN) has still been plagued by the severe recombination of photogenerated electrons and holes, which causes by its poor conductivity and low electron mobility. Herein, in order to enhance the photocharge separation, TiO2 was used to build an interfacial heterojunction with CPCN. Serving as the electron transporter, the used TiO2 nanocrystalline mesoporous film has high specific surface area of 220.03 m2/g. The electrode reaction activity is significantly improved by increasing the interface area between TiO2 and CPCN. Owing to the desirable hole-extraction route for the CPCN photo-rechargeable cell, a remarkable photo-charging capacity of 197 C/g is achieved. The photoelectrode is prepared by coating the CPCN material on top of TiO2 sintered on an fluorine-doped tin oxide(FTO) substrate. The counter electrode is a platinized FTO glass. The electrolyte, using I3-/I- (LiI and I2) in the solution of acetonitrile with a hint of water as the redox shuttle, is injected into the gap between the photoelectrode and the counter electrode to fabricate the cell. The microstructure and morphology of the TiO2 and CPCN materials are characterized by field emission scanning electron microscopy(FESEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), Fourier infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS) and nuclear magnetic resonance spectroscopy(NMR). The photoelectric and electrochemical properties of the TiO2, the CPCN as well as the TiO2/CPCN photoelectrodes are investigated using ultraviolet photoelectron spectroscopy(UPS), UV-Vis absorption spectrum, cyclic voltammetry(CV), galvanostatic charge- discharge(GCD) and electrochemical impedance spectroscopy(EIS).