Efficient photoelectrochemical water splitting and impedance analysis of WO3−x nanoflake electrodes

Solar-powered water splitting with photoelectrochemical (PEC) devices is considered to be a promising method to simultaneously harvest and store solar energy at a large scale. Nanostructured semiconductors offer potential advantages in PEC application due to their large surface area and size-dependent properties, such as increased absorption coefficient, increased band-gap energy and reduced carrier-scattering rate. In this contribution, self-doped tungsten trioxide (WO3−x) nanoflake arrays were synthesized via a new route which involves the dealloying of Fe-W amorphous alloy, thermal treatment in air and properly cathodic polarization. The effects of different cathodic polarization current leading to different x value in WO3−x on the morphology, phase, and photoelectrochemical performance of the resultant samples were investigated. It was found that WO3−x with the appropriate x value presents a dramatic photoelectrochemical current density of 8.7 mA cm−2 in the presence of methanol as a hole scavenger, five folds larger than that of pristine WO3 nanoflakes. UV-vis reflection spectra suggest that the light absorption spectrum range of WO3−x extends from UV to visible light region. Electrochemical impedance spectroscopy disclosed that the unique nanoflake architecture and the surface defects offer improved light harvesting as well as efficient charge transportation.