Enhanced photoelectrochemical water splitting with TiO2@Ag2O nanowire arrays via p-n heterojunction formation

•The novel TiO2@Ag2O p-n heterojunction arrays were fabricated.•The photoelectrochemical performance was enhanced.•The p-n junction affected the Fermi level and increased the separation of electron-hole pairs.•A possible photoelectrochemical mechanism was proposed.

Nanostructured TiO2@Ag2O p-n heterojunction arrays were fabricated by combining the hydrothermal method with the chemical-bath method, and they were used as a photoelectrode in photoelectrochemical (PEC) cell for high-performance solar water splitting. To investigate the morphology, microstructure and composition, the pristine TiO2 nanowire arrays (TiO2 NWAs) and the TiO2 nanowires decorated with Ag2O nanoparticles (TiO2@Ag2O NWAs) were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectra (EIS). Nanostructured TiO2 nanowire arrays were assembled with Ag2O nanoparticles, producing a large number of nano p-n heterojunctions. The TiO2@Ag2O p-n heterojunction arrays showed a photocurrent density of 1.61 mA/cm2 at 1.23 V vs. a reversible hydrogen electrode (RHE) in 0.5 M Na2SO4 electrolyte under simulated AM 1.5 illumination (100 mW/cm2), two times higher than that of the pristine TiO2 NWAs. The enhancement was attributed to the efficient electron-hole separation because of the p-n heterojunction interface between p-Ag2O and n-TiO2, which were revealed by the electrochemical impedance spectra including both Mott-Schottky and Nyquist plots with or without illumination. TiO2@Ag2O p-n heterojunction arrays were expected to have the considerably potential applications in solar water splitting.