Co<sub>3</sub>O<sub>4</sub>‑Modified TiO<sub>2</sub> Nanotube Arrays
via Atomic Layer Deposition for Improved
Visible-Light Photoelectrochemical Performance
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Abstract
Composite
Co<sub>3</sub>O<sub>4</sub>/TiO<sub>2</sub> nanotube
arrays (NTs) were fabricated via atomic layer deposition (ALD) of
Co<sub>3</sub>O<sub>4</sub> thin film onto well-aligned anodized TiO<sub>2</sub> NTs. The microscopic morphology, composition, and interfacial
plane of the composite structure were characterized by scanning electron
microscopy, energy dispersion mapping, X-ray photoelectron spectra,
and high-resolution transmission electron microscopy. It was
shown that the ultrathin Co<sub>3</sub>O<sub>4</sub> film uniformly
coat onto the inner wall of the high aspect ratio (>100:1) TiO<sub>2</sub> NTs with film thickness precisely controlled by the number
of ALD deposition cycles. The composite structure with ∼4 nm
Co<sub>3</sub>O<sub>4</sub> coating revealed optimal photoelectrochemical
(PEC) performance in the visible-light range (λ > 420 nm).
The
photocurrent density reaches as high as 90.4 μA/cm<sup>2</sup>, which is ∼14 times that of the pristine TiO<sub>2</sub> NTs
and 3 times that of the impregnation method. The enhanced PEC performance
could be attributed to the finely controlled Co<sub>3</sub>O<sub>4</sub> coating layer that enhances the visible-light absorption, maintains
large specific surface area to the electrolyte interface, and facilitates
the charge transfer