Cobalt-doped double-layer α-Fe2O3 nanorod arraysfor enhanced photoelectrochemical reduction of Cr(Ⅵ)

Abstract

Element doping is one of the most important methods for improving the performance of photoelectrochemical (PEC) cells. It can change the electronic structure of the catalyst and the separation of the photogenerated charges and increase the carrier density, and thus energy density of the electrode materials. In this study, a Co-doped α-Fe2O3 double-layer electrode was prepared using a two-step hydrothermal method. Scanning electron microscope (SEM) showed that double-layer nanostructures were successfully deposited on a fluorine-doped tin oxide (FTO) substrate using this approach. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the doping did not materially change the morphology of the nanostructures, while diffuse reflectance spectrum (UV-vis DRS) showed that there were only slight changes to the flat bandgap. Electrochemical tests showed that doping greatly improved the current density irrespective of whether the cobalt was doped in the upper or the lower layer. The best performing configuration was that of the FTO/α-Fe2O3:Co/α-Fe2O3 electrode, which achieved a current density of 1.37 mA/cm2. The Co-doped double-layer α-Fe2O3 nanorod arrays proved to possess a high photoelectric synergistic ability for the reduction of Cr (VI) in an aqueous solution, with 84.85% reduction in 180 min. Under the influence of the electric field inside the double-layer electrode, the photoexcited electrons and holes are transferred to the surface of the FTO substrate and the photoanode, increasing the current density. This study offers an alternative approach for designing novel photoanodes with improved PEC performance by engineering the electron density distribution and band structure for efficient carrier separation.