In this work, strong beneficial effects of thin and uniform TiO2 coatings within TiO2 nanotube layers for photocurrent generation and photocatalytical degradation of methylene blue are demonstrated for the first time. TiO2 nanotube layers were coated by TiO2 of various thicknesses (from 2.8 nm to 22 nm) using atomic layer deposition (ALD) and compared with TiO2 nanotube layers decorated by TiO2 nanoparticles (using established TiCl4 treatment) and with blank (uncoated) layers. By means of photocurrent measurements and cyclic voltammetry, it is demonstrated that the most efficient charge carrier separation can be achieved for TiO2 nanotube layers with an optimal ALD TiO2 coating thickness ≈11 nm. Significant differences in flatband potentials and carrier density among all nanotube layers were revealed by Mott-Schottky measurements. Photocatalytic decomposition rates for methylene blue solutions were significantly enhanced for ALD TiO2 coated TiO2 nanotube layers compared to their uncoated or TiO2 nanoparticles - decorated counterparts. A perfect agreement in trends was obtained for photocurrent and photocatalytic results

The authors demonstrate, in this work, a fascinating synergism of a high surface area heterojunction between TiO₂ in the form of ordered 1D anodic nanotube layers of a high aspect ratio and ZnO coatings of different thicknesses, produced by atomic layer deposition. The ZnO coatings effectively passivate the defects within the TiO₂ nanotube walls and significantly improve their charge carrier separation. Upon the ultraviolet and visible light irradiation, with an increase of the ZnO coating thickness from 0.19 to 19 nm and an increase of the external potential from 0.4–2 V, yields up to 8‐fold enhancement of the photocurrent density. This enhancement translates into extremely high incident photon to current conversion efficiency of ≈95%, which is among the highest values reported in the literature for TiO₂ based nanostructures. In addition, the photoactive region is expanded to a broader range close to the visible spectral region, compared to the uncoated nanotube layers. Synergistic effect arising from ZnO coated TiO₂ nanotube layers also yields an improved ethanol sensing response, almost 11‐fold compared to the uncoated nanotube layers. The design of the high‐area 1D heterojunction, presented here, opens pathways for the light‐ and gas‐assisted applications in photocatalysis, water splitting, sensors, and so on.