Preparation of well-aligned WO3 nanoflake arrays vertically grown on tungsten substrate as photoanode for photoelectrochemical water splitting

Well-aligned WO3 nanoflake arrays (WNA) as effective photoanode was vertically fabricated on tungsten sheet through a facile hydrothermal process. Before reaction, the tungsten sheet was pre-annealed to produce a thin-layer WO3 on surface to serve as seeded sites for crystal growth in hydrothermal reaction, which also provided a strong connection between the growing WO3 and substrate. Polyethylene glycol (PEG) was used as the structure-directing agent to confine the crystal growth. This preparation route obviously facilitated the charge transfer and reduced the recombination of photoexcited electron/hole. The saturated photocurrent density and IPCE value were found to be 2.35 mA cm−2 at 1.5 V and 56% which were much higher than that prepared in the absence of pre-annealed WO3 layer and PEG. Keywords: Pre-annealed tungsten substrate, PEG directing, Hydrothermal reaction, WO3 nanoflake arrays, Photoelectrochemical water splitting