Interfacial Construction of Zero-Dimensional/One-Dimensional g-C3N4 Nanoparticles/TiO2 Nanotube Arrays with Z-Scheme Heterostructure for Improved Photoelectrochemical Water Splitting

The OD/1D graphitic carbon nitride (g-C3N4)/TiO2 heterostructures containing an interfacial oxygen vacancy layer were sequentially constructed by anodic oxidation, NaBH4 reduction, and vapor deposition methods. Visible light absorption was significantly improved via construction of the interfacial oxygen vacancy layer and coupling with g-C3N4. Thus, OD/1D g-C3N4/OV-TiO2 showed an optimal photocurrent density as high as 0.72 mA/cm(2) at 1.23 V versus reversible hydrogen electrode under visible light irradiation, 8-fold higher than the data of g-C3N4/TiO2 without interfacial oxygen vacancy layer. Electrochemical impedance spectroscopy (EIS) revealed the OD/1D g-C3N4/OV-TiO2 heterostructured photoanode showed the lowest charge transfer resistance among all the prepared photoanodes. This improved photoelectrochemical (PEC) performance could be attributed to the generation of Z-scheme heterostructure via construction of an interfacial oxygen vacancy layer between TiO2 and g-C3N4. This interfacial layer can promote charge carrier separation and transportation processes. The formation of this Z-scheme heterostructure was confirmed by hydroxyl fluorescence capture characterization and spin-polarized density functional theory calculations. We believe that our work can help rationally design and construct highly efficient heterostructured photoanodes for PEC water splitting applications.