Extracting the limiting factors in photocurrent measurements on TiO2 nanotubes and enhancing the photoelectrochemical properties by Nb doping

Özkan, Selda; Mazare, Anca; Schmuki, Patrik

doi:10.1016/j.electacta.2015.07.023

Cited by 27 publications

(22 citation statements)

References 29 publications

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“…All nanotubes appear smooth and vertically oriented as expected from EG based solutions, and arranged in a closed-pack morphology, which is a common feature for two-step nanotubes [22]. A uniform coverage is obtained and their top surface is clean and free of any hydrous titanium impurities [10] or "nanograss" features [23], which are usually observed in this generation of nanotubes, due to the hydrolysis of TiO 2 during anodization and over-etching, respectively. The morphological parameters of the nanostructured TiO 2 are summarized in Table 1.…”

Section: Microscopic (Sem) and Crystallographic (Xrd) Characterizatiomentioning

confidence: 99%

Assessing the photoelectrochemical properties of C, N, F codoped TiO 2 nanotubes of different lengths

Chatzitakis

Grandcolas

et al. 2017

Catalysis Today

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a b s t r a c tThe aim of this work has been the photoelectrochemical (PEC) study of nanostructured photoanodes based on TiO 2 . Highly ordered and well adhered TiO 2 nanotubes (TNTs) of different lengths (∼2-20 m) were prepared in a two-step process in ethylene glycol solutions containing fluorides, and detailed XPS analysis showed that they have become co-doped with C, N and F. PEC measurements revealed that increasing surface area is not followed by increase in the photoconversion efficiency, but rather that an optimal balance between electroactive surface area (ESA) and charge carrier concentration exists. TNTs of around 10 m show the optimum incident photon-to-current efficiency (IPCE) of ∼33% and an overall photoconversion efficiency of ∼6.3% under UV illumination of 4 mW cm −2 light intensity. Finally, Mott-Schottky analysis revealed significant frequency dispersion of the estimated space charge layer capacitance, which renders the accurate estimation of the flatband position and charge carrier concentration unreliable. On the other hand, more realistic charge carrier concentrations can be obtained by normalizing the capacitance per ESA.

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Section: Microscopic (Sem) and Crystallographic (Xrd) Characterizatiomentioning

confidence: 99%

Assessing the photoelectrochemical properties of C, N, F codoped TiO 2 nanotubes of different lengths

Chatzitakis

Grandcolas

et al. 2017

Catalysis Today

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“…Also, the conversion of TiO 2 nanotubes to semimetallic TiO x C y , by thermal treatment in an acetylene atmosphere, or to TiN nanotubes, by a high temperature treatment in NH 3 , drastically changes the electronic properties of the starting material to a semimetallic nature and also improves its mechanical stability. 200,201 Most recently, high pressure hydrogenation 202 as well as high-energy proton 203 76,78,79,81,205 In particular, in optimally doped and annealed TiO 2 tubes, both Nb and Ta act as electron donors and hence increase the electron conductivity of the NT layers. This was e.g.…”

Section: Tube Morphology and Optical And Electronic Propertiesmentioning

confidence: 99%

Aligned metal oxide nanotube arrays: key-aspects of anodic TiO₂nanotube formation and properties

et al. 2016

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A B S T R A C TOver the past ten years, self-aligned TiO 2 nanotubes have attracted tremendous scientific and technological interest due to their anticipated impact on energy conversion, environment remediation and biocompatibility. In the present manuscript, we review fundamental principles that govern the self-organized initiation of anodic TiO 2 nanotubes. We start with the fundamental question: Why is self-organization taking place? We illustrate the inherent key mechanistic aspects that lead to tube growth in various different morphologies, such as rippled-walled tubes, smooth tubes, stacks and bamboo-type tubes, and importantly the formation of double-walled TiO 2 nanotubes versus single-walled tubes, and the drastic difference in their physical and chemical properties. We show how both double-and single-walled tube layers can be detached from the metallic substrate and exploited for the preparation of robust self-standing membranes.Finally, we show how by selecting the "right" growth approach to TiO 2 nanotubes specific functional features can be significantly improved, e.g., an enhanced electron mobility, intrinsic doping, or crystallization into pure anatase at extremely high temperatures can be achieved. This in turn can be exploited in constructing high performance devices based on anodic TiO 2 in a wide range of applications.

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“…The photoresponse of tubular layers is usually determined by two main phenomena: i) absorption of light and generation of electron‐hole pairs, versus ii) the recombination of the electron‐hole pairs ,. For many TiO 2 nanotube layers used in the UV‐Vis (solar spectral) range, an optimum length typically is some μm for a most efficient photoconversion in aqueous electrolytes ,. Also, the tube diameter influences the photoelectrochemical behavior of NTs; small diameter NTs (mainly in the form of anatase) are reported to be photoelectrochemically more active due to the higher diameter‐dependent population of photo‐generated electrons .…”

Section: Introductionmentioning

confidence: 99%

“…[29,[31][32][33] For many TiO 2 nanotube layers used in the UV-Vis (solar spectral) range, an optimum length typically is some μm for a most efficient photoconversion in aqueous electrolytes. [29,34] Also, the tube diameter influences the photoelectrochemical behavior of NTs; small diameter NTs (mainly in the form of anatase) are reported to be photoelectrochemically more active due to the higher diameterdependent population of photo-generated electrons. [30] Another important characteristic is the crystallinity of nanotubes.…”

Section: Introductionmentioning

confidence: 99%

Optimized Spacing between TiO₂ Nanotubes for Enhanced Light Harvesting and Charge Transfer

et al. 2018

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We investigate two distinctly different anodic TiO2 nanotubular morphologies, spaced and close‐packed arrays. While the close‐packed tubular arrays are formed in ethylene glycol, spaced nanotubes (NTs), which have a regular gap between individual NTs, grow in a diethylene glycol or dimethyl sulfoxide‐based electrolyte. Depending on the electrolyte used for anodization, the morphology, crystal structure, and chemical composition of the resulting nanotubular layer vary from one another. This influences the electrochemical and photoelectrochemical activity of the NTs. Overall, we find that spaced NTs can not only provide enhanced charge‐transfer characteristics but can also show beneficial light absorption characteristics when used as a photo‐ or light‐harvesting electrode.

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Extracting the limiting factors in photocurrent measurements on TiO2 nanotubes and enhancing the photoelectrochemical properties by Nb doping

Cited by 27 publications

References 29 publications

Assessing the photoelectrochemical properties of C, N, F codoped TiO 2 nanotubes of different lengths

Assessing the photoelectrochemical properties of C, N, F codoped TiO 2 nanotubes of different lengths

Aligned metal oxide nanotube arrays: key-aspects of anodic TiO₂nanotube formation and properties

Optimized Spacing between TiO₂ Nanotubes for Enhanced Light Harvesting and Charge Transfer

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Extracting the limiting factors in photocurrent measurements on TiO2 nanotubes and enhancing the photoelectrochemical properties by Nb doping

Cited by 27 publications

References 29 publications

Assessing the photoelectrochemical properties of C, N, F codoped TiO 2 nanotubes of different lengths

Assessing the photoelectrochemical properties of C, N, F codoped TiO 2 nanotubes of different lengths

Aligned metal oxide nanotube arrays: key-aspects of anodic TiO2nanotube formation and properties

Optimized Spacing between TiO2 Nanotubes for Enhanced Light Harvesting and Charge Transfer

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Product

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Aligned metal oxide nanotube arrays: key-aspects of anodic TiO₂nanotube formation and properties

Optimized Spacing between TiO₂ Nanotubes for Enhanced Light Harvesting and Charge Transfer