Enhancing photoelectrochemical performance with a bilayer-structured film consisting of graphene-WO3 nanocrystals and WO3 vertically plate-like arrays as photoanodes

A bilayer-structured film photoelectrode, containing an under-layer of reduced graphene oxide-WO3 nanocrystals (G-WNC) or WO3 nanocrystals (WNC) and a top layer of WO3 vertically plate-like arrays (WP), was designed and fabricated by solution-based and hydrothermal methods. The morphologies, structural and optical properties of as-prepared composites were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet visible (UV-Vis) spectrometry. Moreover, the photoelectrochemical properties were studied through linear scan voltammetry, electrochemical impedance spectroscopy (EIS) and incident photon to current conversion efficiency (IPCE). It was found that the photocurrents of WP, WNC/WP and G-WNC/WP films were 0.68, 0.80 and 1.23 mA cm(-2) at 1.2 V (vs. Ag/AgCl) under AM 1.5G illumination, respectively, whereas the IPCE values were 28.12%, 31.33% and 39.52% successively at the wavelength of 355 nm. EIS data illustrated that the charge transfer resistance was clearly reduced by introducing graphene in the underlayer of the composite film. The enhancement of G-WNC/WP film could be ascribed to the synergic effects of the bilayer structure and the limitation of charge recombination.