Irradiation-induced TiO₂ nanorods for photoelectrochemical hydrogen production

In this work, well-ordered nanorods were fabricated on the surface of TiO₂ thin films deposited on Ti sheets by an ion irradiation method using nitrogen ion irradiation with the energy of 65 keV to a fluence of 1 × 10¹⁷ ions/cm². These TiO₂ nanorods are about 120 nm in length and 20-40 nm in diameter. After post-irradiation annealing at 500 °C in O₂, the nanorod array photoelectrode displays largely enhanced performance for photoelectrochemical (PEC) water splitting compared to that of the un-irradiated TiO₂ thin films with a planar structure. The influences of the irradiated ion energy on the morphology and photocurrent density of the nanorods were investigated. The 65 keV N⁺ irradiated TiO₂ thin films shows a higher photocurrent density than those of the 45 and 85 keV N⁺ irradiated TiO₂ thin films. We also discussed the influence of annealing conditions on the PEC performance of TiO₂ nanorods, and it was found that the nanorods annealed at 600 °C in vacuum produce a much higher photocurrent density of 0.6 mA/cm² at 0.8 V (vs. a saturated calomel electrode), which is about 7 times higher than that of the nanorods annealed in oxygen. This work proposes that ion irradiation combination with thermal annealing in vacuum could be an effective approach for developing nanostructured materials for water splitting.