TiO₂ Nanotube/Chalcogenide-Based Photoelectrochemical Cell: Nanotube Diameter Dependence Study

Abstract

We present photo-electrochemical results for anodic TiO 2 nanotube layers grown with different diameter sizes (21, 35, 56 and 95 nm) with a thickness of approx. 560 nm using a novel anodization protocol. These tube layers were utilized as highly ordered n-type conductive scaffold for the inorganic chromophore Sn-S-Se. While downscaling the nanotube diameter significantly increased the number of nanotubes per square unit (from 5.6E+09 to 7.2E+10 pcs/cm 2 ) and thus the active surface area increased as well, we found that the photoelectrochemical response in the UV light was identical and thus independent of the TiO 2 nanotube diameter in the range of nanotube diameters from 35 to 95 nm. Further, we demonstrate that a heterostructured photo-electrochemical cell consisting of TiO 2 nanotubes sensitized with crystalline Sn-S-Se chromophore showed higher photocurrent density (from 6 to 32 µA/cm 2 for the wavelength of 460 nm) with increasing nanotube diameter size. Upon detailed SEM analyses it was revealed that the Sn-S-Se was infilled in all nanotube layers approximately to one third of the thickness. Therefore, this photocurrent increase with increasing tube diameter can be ascribed to better interfacial contact (and improved charge transport) facilitated between the chromophore and nanotube walls.

CdS-coated TiO2nanotube layers: downscaling tube diameter towards efficient heterostructured photoelectrochemical conversion

“…21 Apparently, the coupling of CdS coatings with TiO 2 nanotube layers causes a strong sensitizing effect, as shown in Fig. 2.…”

Effect of Nickel Doping on Phase Transformation of TiO2 Nanotube Arrays

“…It has been reported that TiO 2 nanotube arrays exhibit higher photoelectrochemical reactivity and photocatalytic activity than most of the conventional nanoparticles, benefited from their high surface area associated with the unique hollow‐tubular and one‐dimension architecture. Because of these advantages, TiO 2 nanotube arrays show promising potential applications in many fields, such as sensors, environment remediation, solar cells, water splitting …”

“…However, the photocatalytic property of TiO 2 photocatalysts was limited by the low visible light response and rapid recombination of photogenerated carries . To overcome these problems, various strategies such as ion doping, quantum dot or dye sensitization, noble metal decoration, additional TiO 2 coating, and heterojunction structure were attempted widely and very good effects have been achieved . In these methods, anatase/rutile heterojunction structure is relative environmental friendly, low‐cost and easy to obtain, and has attracted a lot of interests of researchers.…”

A 1D conical nanotubular TiO2/CdS heterostructure with superior photon-to-electron conversion

“…The enhancement of the IPCE values in the UV spectral region can be ascribed to the presence of sulphur (S) within the TiO 2 nanotube layers which removed TiO 2 surface defects and thus inhibited significant charge carrier recombination. 19 , 20 , 40 , 62 , 63 The surface incorporation of S atoms occurred during the very early ALD cycles as the bare TiO 2 surface and H 2 S came into close contact for a significant time (the exposure time was 45 s). The photoresponse of the CdS/TiO 2 nanotube layers in the visible spectral region was outstanding as compared to their blank counterparts.…”

“…Conventional thin film deposition methods such as chemical vapour deposition (CVD), physical vapour deposition (PVD) or sputtering are not suitable, as the deposited material cannot reach the deepest part of the TiO 2 nanotube layers, and effective utilization of the tube interiors is disabled due to tube mouth clogging. Other attempts, using spin-coating, 19 , 20 electrodeposition, 21 , 22 and chemical bath deposition, 23 , 24 were reported to infiltrate secondary materials in the inner surface of the nanotubes, however complete infiltration of secondary materials was unfortunately constrained to a reduced number of materials.…”