Solar-powered photoelectrochemical (PEC) water splitting has been a promising candidate for producing hydrogen in a clean and renewable way. Photoelectrodes are key components in PEC cells for efficient and stable hydrogen generation because they play crucial roles in absorption of photons, the separation and transportation of photo-generated charge carriers, as well as the chemical reactions with water. A variety of metal oxides for efficient photoelectrode have been intensively explored, but it is still challenging to find desirable materials to satisfy lots of requirements for PEC water splitting.

Iron oxide (hematite, Fe₂O₃) has recently attracted much attention due to its earth abundance, low cost as well as desirable material properties for PEC water oxidation including narrow band gap energy of 2.0~2.2eV for visible light absorption and proper energy band alignment, etc. However, Fe₂O₃ has very short hole diffusion length and low carrier mobility, which causes considerable recombination of photo-generated electrons and holes. A lot of approaches such as nanostructures, heterojunction with other materials, surface modification, etc. have been reported to improve electrical properties of Fe₂O₃ which unfortunately cause poor light absorption.

In this study, three-dimensional tin oxide (SnO₂) nanohelix (NH) structures were fabricated as scaffolds for a thin Fe₂O₃ layer on fluorine-doped SnO₂ glass substrate by oblique angle deposition method using electron beam evaporator. SnO₂ NH structures based photoelectrode can simultaneously enhance light absorption and charge separation and transport for efficient PEC water splitting by trapping the incident light through strong light scattering effect as well as by providing pathways for charge separation and transport and large surface area. In addition, SnO₂ NH structures are easy to be hybridized with Fe₂O₃ through only simple solution-based spin-coating method due to its high porosity, aspect ratio and large surface area. Thin Fe₂O₃ layer was coated along the surface of SnO₂ NH structures forming a type-II band hetero-junction and these Fe₂O₃ coated SnO₂ NH are significantly desirable for efficient visible light driven water splitting by simultaneously improving light absorption, charge separation and transport. Highly efficient PEC performance of our hybridized photoelectrode (including more than 5.0mAcm^-2 photocurrent density at 1.23V_RHE under AM1.5G solar spectrum and 1 sun illumination which is a significantly excellent performance for Fe₂O₃ based photoelectode) will be investigated and the advantages of three-dimensional SnO₂ NH structures as scaffolds for very thin Fe₂O₃ layer as well as its potential for practical application will be discussed in detail based on electrochemical analysis, FEM simulation, angular-dependent reflectance, PEC analysis at different intensity of incident light, etc.