Ce-doped CdS quantum dot sensitized TiO2 nanorod films with enhanced visible-light photoelectrochemical properties

Ce-doped CdS quantum dot (QD) sensitized TiO2 nanorods films on FTO substrates are for the first time prepared by a combination of hydrothermal and successive ionic layer adsorption and reaction (SILAR) method. The physicochemical properties of as-prepared samples are examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectrometry (UV-vis). The as-prepared Ce-CdS QD sensitized TiO2 nanorods photoelectrodes is applied into photoelectrochemical (PEC) cells to investigate their PEC properties, including the photocurrent density and incident photon-to-current conversion efficiency (IPCE), which exhibit a maximum 1.4-time enhancement in photocurrent density and 1.6-time enhancement in IPCE value, compared with undoped photoelectrode. Furthermore, a maximum 1.4-time higher formic acid yields was obtained in a versatile photoanode-driven PEC CO2 reduction system. The results of electrochemical analysis show that the Ce-CdS QDs/TiO2 photoelectrodes exhibit an increased visible light absorbance, a higher carrier density, a longer electron lifetime and more effective separation of photogenerated electron-hole pairs. This is most probably due to the existence of Ce 4f electronic states in the mid-gap region of Ce-CdS QDs, which is confirmed by a simple theoretical calculation and a redox couple Ce3+/Ce4+ accelerating the photogenerated holes migration. The study demonstrates that the variable valency Ce-doping may be a promising approach to achieve high photoelectric conversion efficiency for chalcogenides semiconductors.