Facile Synthesis of [101]-Oriented Rutile TiO₂ Nanorod Array on FTO Substrate with a Tunable Anatase–Rutile Heterojunction for Efficient Solar Water Splitting

Generating a sustainable energy source through photoelectrochemical (PEC) water splitting requires a suitable photocatalyst. A [101]-oriented rutile TiO2 nanorod (NR) array in heterojunction with anatase on a fluorine-doped tin oxide (FTO) substrate is successfully prepared using a facile single-step hydrothermal process. The presence of anatase phase over the predominant rutile NRs’ surface is confirmed by transmission electron microscopy and tip-enhanced Raman spectroscopy. Solar water-splitting performances of anatase–rutile heterojunction with low energy (101) and high energy (001) rutile facets are compared. The low energy (101) facet rutile–anatase heterojunction shows higher photoconversion efficiency of 1.39% at 0.49 VRHE than the high energy (001) facet rutile–anatase heterojunction (0.37% at 0.73 VRHE). The mechanism for enhanced photocatalytic activity of the low energy (101) facet rutile–anatase heterojunction has been proposed. The role of NaCl in tuning the anatase portion, morphology, and PEC water-splitting performance has also been studied.