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AuthorJeong H.W.
AuthorPark K.J.
AuthorPark Y.
AuthorHan D.S.
AuthorPark H.
Available date2020-04-23T14:21:34Z
Publication Date2019
Publication NameCatalysis Today
ResourceScopus
ISSN9205861
URIhttp://dx.doi.org/10.1016/j.cattod.2018.12.014
URIhttp://hdl.handle.net/10576/14368
AbstractAlthough one-dimensional TiO2 nanotube arrays (TNA) grown on Ti substrates via electrochemical anodization are extensively studied in photoelectrochemistry, the photo(electro)catalytic activity of TNA detached from the Ti substrates remains unexplored. Herein, we synthesize TNA samples with various pore sizes (40–100 nm) and tube lengths (4–15 μm) via two-step electrochemical anodization, and transfer them to transparent conducting oxide (i.e. fluorine-doped tin oxide; FTO) substrates in normal (n) alignment (front plane outward) and reverse (r) alignment (backplane outward). The front and back planes of the as-fabricated TNA film are the same based on X-ray diffraction (anatase structure), X-ray photoelectron spectroscopy (Ti and O), and UV–vis transmittance data, though the tubes are open in the front and closed in the back. Regardless of the direction of irradiation (SE: FTO → TNA vs. EE: TNA → FTO), longer tubes generate a higher photocurrent (Iph) due to the large light absorption. However, for the same alignment of TNA (either n- or r-TNA), SE irradiation leads to a very large Iph (e.g., nSE > nEE), whereas n-TNA consistently generates a larger Iph than r-TNA for a given irradiation direction (i.e., n > r). The photocatalytic decomposition of phenol follows the same tendency (n > r); however, the Faraday efficiency (based on the photocharge) is higher with EE (nEE 28%, rEE 20%) than SE (rSE 11%, nSE 7%) irradiation. These photoelectrochemical and photocatalytic behaviors are explained in terms of charge carrier generation (FTO/TNA vs. TNA/solution), dissimilar charge carrier transfer pathways (e− transfer through tube framework vs. h+ transfer via radial direction), and charge injection at the tube (open vs. clogged tube mouth)/solution interface. The time-resolved photoluminescence (TRPL) emission and incident photon-to-current efficiency (IPCE) are also studied to gain insight into the charge transfer kinetics.
SponsorThis research was supported by the Basic Science Research Program ( 2016R1A2B4007366 and 2018R1A6A1A03024962 ), Space Core Technology Development Program ( 2014M1A3A3A02034875 ), Framework of International Cooperation Program ( 2017K2A9A1A01092948 , FY2017 ), and Next-Generation Carbon Upcycling Project ( 2017M1A2A2043123 ) through the National Research Foundation, Korea . This publication was made possible by a grant from the Qatar National Research Fund under its National Priorities Research Program (NPRP 10-1210-160019). Appendix A
Languageen
PublisherElsevier B.V.
SubjectAnodization
Charge transfer
Morphology
Photocatalysis
Photoelectrochemistry
TitleExploring the photoelectrocatalytic behavior of free-standing TiO2 nanotube arrays on transparent conductive oxide electrodes: Irradiation direction vs. alignment direction
TypeArticle
Pagination319-325
Volume Number335


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