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Photoelectrochemical Performance of Quantum dot-Sensitized TiO 2 Nanotube Arrays: a Study of Surface Modification by Atomic Layer Deposition Coating

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ABSTRACT

Although CdS and PbS quantum dot-sensitized TiO2 nanotube arrays (TNTAs/QDs) show photocatalytic activity in the visible-light region, the low internal quantum efficiency and the slow interfacial hole transfer rate limit their applications. This work modified the surface of the TNTAs/QDs photoelectrodes with metal-oxide overlayers by atomic layer deposition (ALD), such as coating Al2O3, TiO2, and ZnO. The ALD deposition of all these overlayers can apparently enhance the photoelectrochemical performance of the TNTAs/QDs. Under simulated solar illumination, the maximum photocurrent densities of the TNTAs/QDs with 10 cycles ZnO, 25 cycles TiO2, and 30 cycles Al2O3 overlayers are 5.0, 4.3, and 5.6 mA/cm2 at 1.0 V (vs. SCE), respectively. The photoelectrode with Al2O3 overlayer coating presents the superior performance, whose photocurrent density is 37 times and 1.6 times higher than those of the TNTAs and TNTAs/QDs, respectively. Systematic examination of the effects of various metal-oxide overlayers on the photoelectrochemical performance indicates that the enhancement by TiO2 and ZnO overcoatings can only ascribed to the decrease of the interfacial charge transfer impedance, besides which Al2O3 coating can passivate the surface states and facilitate the charge transfer kinetics. These results could be helpful to develop high-performance photoelectrodes in the photoelectrochemical applications.

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TEM images of TNTAs/QDs with various ALD cycles overlayer: a 0 cycles, b 30 cycles Al2O3, c 10 cycles ZnO, and d 25 cycles TiO2. The insets are the corresponding low-resolution TEM images
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Fig2: TEM images of TNTAs/QDs with various ALD cycles overlayer: a 0 cycles, b 30 cycles Al2O3, c 10 cycles ZnO, and d 25 cycles TiO2. The insets are the corresponding low-resolution TEM images

Mentions: Figure 2 is the high-resolution TEM (HRTEM) images of the TNTAs/QDs both before and after the metal-oxide layer deposition. The illustration in the insets is the corresponding low-resolution TEM images. It can be seen that the quantum dots are evenly distributed on the TiO2 nanotubes with a particle size of approximately 8 nm. It can be seen from Fig. 2b–d that a smooth, uniform, and light-color layer with thickness of approximately 1.5 ± 0.5 nm is wrapped outside the TNTAs/QDs. The thin layer are Al2O3, ZnO, and TiO2 coating, respectively. In Fig. 2a, the spacing of 3.29 and 3.58 Å, respectively, correspond to the (111) lattice plane of the cubic phase CdS (JCPDS No. 89-0440) and the (101) lattice plane of the TiO2 anatase type (JCPDS 21-1272); in Fig. 2d, the lattice spacing of 2.97 Å correspond to the (200) lattice plane of the cubic phase PbS.Fig. 2


Photoelectrochemical Performance of Quantum dot-Sensitized TiO 2 Nanotube Arrays: a Study of Surface Modification by Atomic Layer Deposition Coating
TEM images of TNTAs/QDs with various ALD cycles overlayer: a 0 cycles, b 30 cycles Al2O3, c 10 cycles ZnO, and d 25 cycles TiO2. The insets are the corresponding low-resolution TEM images
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig2: TEM images of TNTAs/QDs with various ALD cycles overlayer: a 0 cycles, b 30 cycles Al2O3, c 10 cycles ZnO, and d 25 cycles TiO2. The insets are the corresponding low-resolution TEM images
Mentions: Figure 2 is the high-resolution TEM (HRTEM) images of the TNTAs/QDs both before and after the metal-oxide layer deposition. The illustration in the insets is the corresponding low-resolution TEM images. It can be seen that the quantum dots are evenly distributed on the TiO2 nanotubes with a particle size of approximately 8 nm. It can be seen from Fig. 2b–d that a smooth, uniform, and light-color layer with thickness of approximately 1.5 ± 0.5 nm is wrapped outside the TNTAs/QDs. The thin layer are Al2O3, ZnO, and TiO2 coating, respectively. In Fig. 2a, the spacing of 3.29 and 3.58 Å, respectively, correspond to the (111) lattice plane of the cubic phase CdS (JCPDS No. 89-0440) and the (101) lattice plane of the TiO2 anatase type (JCPDS 21-1272); in Fig. 2d, the lattice spacing of 2.97 Å correspond to the (200) lattice plane of the cubic phase PbS.Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

Although CdS and PbS quantum dot-sensitized TiO2 nanotube arrays (TNTAs/QDs) show photocatalytic activity in the visible-light region, the low internal quantum efficiency and the slow interfacial hole transfer rate limit their applications. This work modified the surface of the TNTAs/QDs photoelectrodes with metal-oxide overlayers by atomic layer deposition (ALD), such as coating Al2O3, TiO2, and ZnO. The ALD deposition of all these overlayers can apparently enhance the photoelectrochemical performance of the TNTAs/QDs. Under simulated solar illumination, the maximum photocurrent densities of the TNTAs/QDs with 10 cycles ZnO, 25 cycles TiO2, and 30 cycles Al2O3 overlayers are 5.0, 4.3, and 5.6 mA/cm2 at 1.0 V (vs. SCE), respectively. The photoelectrode with Al2O3 overlayer coating presents the superior performance, whose photocurrent density is 37 times and 1.6 times higher than those of the TNTAs and TNTAs/QDs, respectively. Systematic examination of the effects of various metal-oxide overlayers on the photoelectrochemical performance indicates that the enhancement by TiO2 and ZnO overcoatings can only ascribed to the decrease of the interfacial charge transfer impedance, besides which Al2O3 coating can passivate the surface states and facilitate the charge transfer kinetics. These results could be helpful to develop high-performance photoelectrodes in the photoelectrochemical applications.

No MeSH data available.