Titanium-Doped Hematite Homojunction Photoanodes Based on Nanorod/Nanobowl Arrays for Efficient Solar Water Splitting

Hematite is a promising candidate material for photoanodes, but the efficiency of the state-of-the-art hematite photoanodes is limited by the low absorption coefficient, short hole diffusion length, and slow water oxidation kinetics. In this work, a high-efficiency hematite photoanode was designed and fabricated by introducing titanium-doped hematite (Ti:Fe₂O₃) homojunction with different doping contents and a hierarchical nanorod/nanobowl array structure. The homojuction consisted of low Ti doping nanorods grown on high Ti doping nanobowl arrays, leading to the formation of a broad built-in electric field, significantly enhancing the charge separation and transfer within the bulk. Furthermore, the nanorods radially grown inside the bowls and on the bowl edges enabled enhanced light absorption through multiple light scattering while offering a larger electrode–electrolyte contact area and providing more reaction sites. Compared to the Ti:Fe₂O₃ nanorod arrays, the Ti:Fe₂O₃ nanorod/nanobowl array photoanode exhibited an increase in photocurrent density from 1.6 mA cm⁻² to 3.0 mA cm⁻² at 1.23 V versus RHE, maintaining long-term stability over 100 h at 1.23 V versus RHE. This study not only achieved a high-performance hematite photoanode but also provided a new perspective on the design of differently doping homojunction photoanodes with desired nanostructures.