ZnO Coated Anodic 1D TiO₂ Nanotube Layers: Efficient Photo‐Electrochemical and Gas Sensing Heterojunction

Abstract

The authors demonstrate, in this work, a fascinating synergism of a high surface area heterojunction between TiO 2 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 TiO 2 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 TiO 2 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 TiO 2 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.

MoSexOy‐Coated 1D TiO2 Nanotube Layers: Efficient Interface for Light‐Driven Applications

“…In order to provide an additional proof of MoSe x O y successful coatings, the energy‐dispersive X‐ray spectroscopy (EDX) elemental mapping and line scan of the 50 cycles MoSe x O y ‐coated TiO 2 nanotube layer taken from the interface of the bottom part of the TiO 2 nanotube layer and the underlying Ti substrate is shown in Figures S1 and S2 (Supporting Information). Similar uniform and ultrathin coatings within TiO 2 nanotube layers were also observed in our previous works for various secondary materials, including Al 2 O 3 , TiO 2 , ZnO, and CdS . By measuring the thickness of the MoSe x O y shown in Figure a,b, we estimate that the thickness of the 50 cycles MoSe x O y coating is ≈10 nm.…”

Spaced TiO2 Nanotubes Enable Optimized Pt Atomic Layer Deposition for Efficient Photocatalytic H2 Generation

“…In contrast, atomic layer deposition (ALD) can yield the uniform deposition of complex nanostructures and allows for a controlled loading amount by varying the number of ALD cycles . Also, it provides precise thickness control conformability on high‐aspect‐ratio nanostructures …”

“…[17,18] Also, it providesp recise thickness control conformability on high-aspect-ratio nanostructures. [19,20] In the presentw ork, we evaluate the deposition of Pt by using ALD into SP and CP TiO 2 NTsu sing different numberso f ALD cycles, which influences the size and density of Pt nanoparticles. The objective is to maximize the H 2 evolution rate of platinized SP TiO 2 NTsu nder UV and solarl ight, and compare the results with conventional CP TiO 2 NTs.…”

Electrochemically anodized one-dimensional semiconductors: a fruitful platform for solar energy conversion

“…Particularly, PEC water splitting has been deeming as a 'Holy Grail' of modern science [5,154]. Aligned porosity, good crystallinity, and oriented nature of nanotube or nanoporous structure make anodized 1D semiconductors ideal candidates for PEC water splitting [153,155,156]. For instance, more recently, as displayed in figure 22, hierarchical Fe 2 O 3 nanostructures with multidimensional nano/microarchitectures were constructed by electrochemical anodization of Fe foams (AFF) were directly used as photoanodes for PEC water splitting [153].…”