Growth of nano-branches on 1-D WO3 nanotrees by flame process and its photoelectrochemical performances

Flame vapor deposition (FVD) is a powerful method to prepare rapidly and economically the nanostructured thin film with high purity and high crystallinity. One-dimensional (1-D) nanostructured tungsten oxide (WO3) thin film has high potential for various applications as photocatalytic material and, in this study, was prepared from tungsten wire as a precursor by FVD process. The nucleation and growth rates in FVD process could be controlled by changing the precursor supply rate in flame instantaneously by installing additional wire traverse feeder and the nanotree structured WO3 thin film was prepared successfully. The concentration of nano-branches at nanotree structured WO3 thin films could be controlled by adjusting wire traversing speed. The proper wire traverse feeding speed could increase surface area and allow more light absorption by additional growth of nano-branches, but too low wire traverse feeding speed could make random and dense growth of nano-branches to reduce the electrical properties and total surface area. The proper growth of nano-branches could increase the photoelectrochemical (PEC) performance of WO3/BiVO4 heterojunction thin film by providing the larger interfacial contact area for heterojunction, but too much growth of nano-branches could reduce the PEC performance because of non-uniform loading of BiVO4 in WO3 thin film during spin-coating process. This study can be a basis to prepare by FVD process not only the nanotree structured WO3 thin film for its PEC application but also many nanostructured thin films of various materials for their suitable applications. [Display omitted] •Nanotree structured WO3 thin film was successfully prepared by 1-step flame process.•The precursor concentration could be changed sharply by the wire traversing feeder.•Nucleation and growth rates were controlled to prepare nano-branches on nanotrees.•Nanotree structured WO3/BiVO4 film improved photoelectrochemical performance.•Proper growth of nano-branch is important for high photoelectrochemical performance.