Directing WO3 crystal growth towards artificial photosynthesis favorable {002} plane via aluminum incorporation in the lattice for enhanced water splitting

Highlights: • {002} facet oriented WO₃ thin films were obtained via aluminum doping. • Aluminum doping decreases the charge transport resistance of bulk WO₃. • Decrease in charge transfer resistance across electrode/electrolyte interface. • Al-doped WO₃ show higher photocurrent values compared to undoped WO₃. • Oxygen production increased significantly after the Al doping. -- Abstract: The {002} oriented WO₃ is known to exhibit superior photoelectrochemical (PEC) water splitting O₂ production compared to other facets and is generally produced via facet oriented synthesis schemes. Such schemes generally decrease surface charge transfer properties but do not alter/change the bulk charge transport characteristics. In this work, Al doping strategy is proposed to fabricate {002} facet orientated WO₃ crystals with improved bulk electrical properties. Importantly, the incorporation of Al into WO₃ lattice was found to decrease the resistance for bulk charge transport as well as the resistance for charge transfer between the interface of electrode and electrolyte. The optimized at% of Al-doped WO₃ exhibited enhanced PEC and incident photon to current efficiencies compared to bare WO₃. The proposed strategy indicates that doping with suitable material using proper synthetic scheme could be an efficient and alternate route to obtain WO₃ nanocrystals with desired crystal orientation, optical and bulk electrical properties.