Enhancing photoelectrochemical activity of CdS quantum dots sensitized WO3 photoelectrodes by Mn doping

Abstract

Mn-doped CdS quantum dots sensitized WO₃ photoelectrodes were successfully synthesized by a combination of hydrothermal and chemical bath deposition (CBD) methods. To improve the stability of the photoelectrodes in an alkaline environment, the electrodes were treated with TiCl₄ to form a nano-TiO₂ buffer layer on the WO₃ plate surface before depositing CdS quantum dots (QDs). The resulting electrodes were applied as photoanodes in the photoelectrochemical cell for water splitting. The photoelectrochemical (PEC) properties were investigated by the photocurrent density curves and incident photon-to-current conversion efficiency (IPCE). The as-prepared Mn-CdS QDs sensitized WO₃ plate-like photoelectrodes exhibit a significant improvement in their photoelectrochemical performance compared with undoped photoelectrodes. To better understand the enhanced PEC properties, the electron transport properties and efficient electron lifetime were studied in detail using electrochemical impedance spectroscopy (EIS), transient photocurrent spectroscopy and intensity modulated photocurrent spectroscopy (IMPS). The results show that the Mn-CdS QDs/TiO₂/WO₃ photoelectrodes exhibit a higher electron transit rate and a longer electron lifetime. This is most likely due to the existence of electronic states in the mid-gap region of the Mn-CdS QD.