Morphological Control Effect of Hierarchical Heterostructure α-Fe₂O₃/TiO₂ Nanotube for Photoelectrochemical Water Splitting

Abstract

Large-band gap metal oxide TiO 2 have suitable band positions for photoelectrochemical cells (PECs) for solar-driven water splitting, but uses only UV light region in the solar spectrum which represent only about 5 % of the energy. On the other hand, α-Fe 2 O 3 with suitable bandgaps for efficient absorption in the solar spectrum require an external bias to drive hydrogen generation at the cathode due to the conduction band of α-Fe 2 O 3 below the H 2 evolution potential and have short carrier diffusion lengths. Synthesizing the metal oxide nanomaterials which have both suitable band position to drive reaction and visible light absorbed band gap is one of the major challenge in PECs for water splitting field. Hetero structure of α-Fe 2 O 3 and TiO 2 offer a potential solution to improve this problem. However, the inherent low electrical conductivity resulting in the high electron-hole pair recombination rate and short carrier diffusion length of α-Fe 2 O 3 limit its practical use. Here we report a novel hierarchical heterostructure of α-Fe 2 O 3 ultrathin nanoflakes branched on TiO 2 nanotube strategy for PECs for water splitting. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that suitable morphological control of α-Fe 2 O 3 and TiO 2 plays an important role in enhancing the photoelectrochemical water splitting performance.