Triple-layered nanostructured WO₃ photoanodes with enhanced photocurrent generation and superior stability for photoelectrochemical solar energy conversion

Unique nanorods/nanoparticles/nanoflakes (NRs/NPs/NFs) WO₃ triple-layers are grown on a metallic W foil by a simple one-step anodization method. The triple-layered structure is formed through a self-organization process, the film thickness (up to 3 μm) being controlled by the anodization time. A first layer made of an array of WO₃ densely-packed vertically-aligned NRs (1.2-1.4 μm in height) grow atop the tungsten foil, followed by a second layer of small NPs (50-80 nm) and finally a third layer made of rectangular NFs (200-300 nm). When irradiated by white light in a photoelectrochemical cell these WO₃ triple-layers generate a photocurrent as high as 0.9 mA cm^-2 at 1.2 V/RHE. Moreover, we show that the stability of the triple-layered WO₃ photoanodes can be considerably enhanced by adding an ultrathin (10 nm) TiO₂ protective overlayer.