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. 2015 Jun 12:5:10461.
doi: 10.1038/srep10461.

Plasmonic silver quantum dots coupled with hierarchical TiO2 nanotube arrays photoelectrodes for efficient visible-light photoelectrocatalytic hydrogen evolution

Zichao Lian  1 , Wenchao Wang  1 , Shuning Xiao  1 , Xin Li  1 , Yingying Cui  1 , Dieqing Zhang  1 , Guisheng Li  1 , Hexing Li  1
Affiliations

Plasmonic silver quantum dots coupled with hierarchical TiO2 nanotube arrays photoelectrodes for efficient visible-light photoelectrocatalytic hydrogen evolution

Zichao Lian et al. Sci Rep. .

Abstract

A plasmonic Ag/TiO2 photocatalytic composite was designed by selecting Ag quantum dots (Ag QDs) to act as a surface plasmon resonance (SPR) photosensitizer for driving the visible-light driven photoelectrocatalytic hydrogen evolution. Vertically oriented hierarchical TiO2 nanotube arrays (H-TiO2-NTAs) with macroporous structure were prepared through a two-step method based on electrochemical anodization. Subsequently, Ag QDs, with tunable size (1.3-21.0 nm), could be uniformly deposited on the H-TiO2 NTAs by current pulsing approach. The unique structure of the as-obtained photoelectrodes greatly improved the photoelectric conversion efficiency. The as-obtained Ag/H-TiO2-NTAs exhibited strong visible-light absorption capability, high photocurrent density, and enhanced photoelectrocatalytic (PEC) activity toward photoelectrocatalytic hydrogen evolution under visible-light irradiation (λ>420 nm). The enhancement in the photoelectric conversion efficiency and activity was ascribed to the synergistic effects of silver and the unique hierarchical structures of TiO2 nanotube arrays, strong SPR effect, and anti-shielding effect of ultrafine Ag QDs.

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Figures

Figure 1
Figure 1. XRD spectra.
XRD patterns of (a) the as-prepared H-TiO2-NTAs, and Ag/H-TiO2-NTAs with various pulse electro-deposition time of (b) 10 s, (c) 20 s, (d) 50 s, (e) 100 s.
Figure 2
Figure 2. FESEM, TEM images and size distribution.
Top view of FESEM image (a) cross-section view FESEM image (b) of H-TiO2-NTAs, (c) TEM image of 20s-Ag/H-TiO2-NTAs, and (d) size distribution of Ag QDs located on the pore wall of 20s-Ag/H-TiO2-NTAs.
Figure 3
Figure 3. Schematic diagram.
The light penetration mechanism in the Ag nanocrytals loaded H-TiO2-NTAs.
Figure 4
Figure 4. XPS analysis.
High resolution XPS of (a) Ag 3d of 20s-Ag/H-TiO2-NTAs and (b) Ti 2p of H-TiO2-NTAs and 20s-Ag/H-TiO2-NTAs.
Figure 5
Figure 5. Electrochemical testing and Photoluminescence.
(a) Nyquist plot of electrochemical impedance spectra, (b) Mott-Schottky plots, and (c) photoluminescence (PL) spectra with the excited wavelength at 280 nm of H-TiO2-NTAs, 20s Ag/H-TiO2-NTAs, and 20s Ag/TiO2-NTAs.
Figure 6
Figure 6
Photoelectrochemical properties of the pure and Ag QDs modified H-TiO2-NTAs and schematic diagram of SPR charge carrier transfer mechanisms. (a) Photocurrent responses in the light on-off process (0.7 V vs. SCE): under illumination of visible light with wavelength >420 nm with 20 s light on/off cycles. (b) SPR charge carrier transfer under visible light irradiation at Ag/H-TiO2 interface and the PEC process for H2 evolution. (c) DRS of H-TiO2-NTAs, Ag/TiO2 and Ag/H-TiO2-NTAs with different deposition time: 10 s, 20 s, 50 s, 100 s.
Figure 7
Figure 7. Size of Ag QDs and photocatalytic H2 production.
(a) The size of Ag quantum dots via the pulse electron-deposition time; (b) the hydrogen evolution rate by using various samples as photoanodes and Pt foil as cathodes, at 0.7 vs. SCE in a PEC cell containing a 2 M ethylene glycol and 0.5 M Na2SO4 solution under 300 W Xe lamp (>420 nm filter) irradiation.
Figure 8
Figure 8. Schematic diagram of the Ag/H-TiO2-NTAs fabrication procedure.
(a) Ti foil, (b) first anodized TiO2 nanotubes, (c) nanoprints left on the Ti foil, (d) Second anodized on the TiO2 NTAs, (e) Ag QDs deposition on the H-TiO2-NTAs via a pluses deposition, (f) Top larger pore enhancing SPR of Ag QDs and multiple reflections in the H-TiO2-NTAs.
Figure 9
Figure 9. Schematic representation of H2 production device.
Schematic diagram of the home-made gas generation.
See this image and copyright information in PMC

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