Metal-sulfide-decorated ZnO/Si nano-heterostructure arrays with enhanced photoelectrochemical performance

doi:10.1016/j.materresbull.2017.05.017

Materials Research Bulletin

Volume 96, Part 4, December 2017, Pages 503-508

https://doi.org/10.1016/j.materresbull.2017.05.017 Get rights and content

Highlights

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A facile approach to fabricate perfectly ordered arrays of metal sulfides ZnO/Si.
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The significant enhancement of ZnO/Si heterostructure arrays in photo-current density and on/off ratio as a photoanode.
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Metal-sulfide-coated ZnO/Si heterostructure arrays are a promising building block photoelectrochemical cells.

Abstract

The present work reports an effective approach to fabricate highly ordered arrays of ZnO/Si heterostructures decorated with metal sulfides (i.e. ZnS and Ag₂S). These metal-sulfide-coated ZnO/Si heterostructure arrays are then used as a photoanode in the photoelectrochemical water splitting system. The significant enhancement of ZnO/Si heterostructure arrays in photo-current density and on/off ratio is demonstrated after they are coated with metal sulfides. These metal-sulfide-coated ZnO/Si heterostructure arrays are a promising building block for the fabrication of optoelectronic devices such as photoelectrochemical cells.

Graphical abstract

Introduction

ZnO and TiO₂ are two excellent optoelectronic materials due to their wide direct band gap, low cost and facial fabrication. The larger exciton binding energy (60 meV vs 4 meV), higher electron mobility (200 cm² V⁻¹ s⁻¹ vs 30 cm² V⁻¹ s⁻¹) and, more importantly, better conductivity of ZnO than TiO₂ render it an ideal candidate of photoelectrode in the photoelectrochemical (PEC) system. However, the poor stability of ZnO in both acidic and alkaline electrolytes [1] and the low efficiency in the visible light region have restrained it from the practical applications so far [2]. To overcome these problems, ZnO nano-heterostructures are designed and synthesized through the incorporation of photocatalytic and anti-corrosive components [3].

It is expected that the ZnO nano-heterostructures are tailored to not only improve the chemical stability of ZnO but also significantly enhance the photocatalytic activity by increasing both light absorption and charge separation [4]. Furthermore, three-dimensional nano-heterostructure arrays with desirable surface morphology provide a large surface area for the surface redox reaction [5], so as to increase gas evolution on the large surface curvature [6] and augment the higher absorption of the solar light [7].

In the present paper, an approach is introduced to fabricate highly ordered metal-sulfide-coated ZnO/Si heterostructure arrays which are demonstrated as a photoelectrode suitable for the application in the PEC system. The Si substrate deposited with a thin seed layer of ZnO was first patterned, to create the ordered Si nanocone array using the method that we developed and was described in detail in the published paper [8]. The obtained nanocone array was subsequently immersed into a mixed solution of zinic nitrate hexhydrate and hexamethylenetetramine (HMTA). Hydrothermal method was then used to grow ZnO nanorods on top of each nanocone forming a highly ordered ZnO/Si heterostructure array [9]. After that, the heterostructure array was transferred into the solution of thioacetamide (TAA) and then AgNO₃ sequentially forming the Ag₂S/ZnS/ZnO multiple core/shell nanorod structures arrays, as observed in scanning electron microscopy (FEI Nova 600 Dual Beam SEM/FIB). Transmission electron microscopy (JEOL 2100F TEM) was used and operated at 200 KeV to clarify the microstructures of nanorods. The performance evaluation demonstrates that ZnO/Si nano-heterostructure arrays show the significant enhancement in photocurrent density and on/off ratio after being decorated with metal sulfides.

Section snippets

Results and discussion

Fig. 1 shows a sequence of secondary electron images of the samples taken at an inclined angle of 52° in SEM, including ZnO/Si nano-heterostructures (a), ZnS/ZnO/Si nano-heterostructures (b) and Ag₂S/ZnS/ZnO/Si nano-heterostructures (c), and the cross section SEM image of Ag₂S/ZnS/ZnO/Si nano-heterostructures (d). Each Si nanocone is measured to have a height of around 500 nm and 500 nm apart from the adjacent nanocones. It is advantageous that the height and space of nanocones are simply

Conclusions

In this work, a novel approach for the fabrication of highly ordered and vertically aligned ZnO/Si nano-heterostructure array followed by the sequential decoration with metal sulfides (i.e. ZnS and Ag₂S) is reported. Evaluation of the performance of the heterostructure array acting as anode in photoelectrochemical system demonstrates that the decoration with metal sulfides allows the significant improvement of photocurrent density and on/off ratio in comparison with the pure ZnO/Si nanoarray

Acknowledgments

This research was support by SUG (Start-up funding in NTU), Tier 1 (AcRF grant MOE Singapore M4011528 RG99/15), Tier 2 (AcRF grant MOE Singapore M4020159) and the Chinese Natural Science Foundation (Grant 60906053, 62174118 and 51308050309).

References (13)

S.A. Ivanov et al.
Type-II core/shell CdS/ZnSe nanocrystals: synthesis, electronic structures, and spectroscopic properties
J. Am. Chem. Soc.
(2007)
A. Kargar et al.
Tailoring n-ZnO/p-Si branched nanowire heterostructures for selective photoelectrochemical water oxidation or reduction
Nano Lett.
(2013)
R.S. Devan et al.
One-dimensional metal-oxide nanostructures: recent developments in synthesis, characterization, and applications
Adv. Funct. Mater.
(2012)
M. Zhong et al.
ZnO-ZnGa2O4 core-shell nanowire array for stable photoelectrochemical water splitting
Nanoscale
(2012)
A. Sheikh et al.
Near-field plasmonic functionalization of light harvesting oxide-oxide heterojunctions for efficient solar photoelectrochemical water splitting: the AuNP/ZnFe2O4/ZnO system
Small
(2013)
Y.J. Hwang et al.
High density n-Si/n-TiO2 core/shell nanowire arrays with enhanced photoactivity
Nano Lett.
(2009)
H.S. Song et al.
Controllable fabrication of three-dimensional radial ZnO nanowire/silicon microrod hybrid architectures
Cryst. Growth Des.
(2011)

There are more references available in the full text version of this article.

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Metal-sulfide-decorated ZnO/Si nano-heterostructure arrays with enhanced photoelectrochemical performance

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

Conclusions

Acknowledgments

J. Am. Chem. Soc.

Tailoring n-ZnO/p-Si branched nanowire heterostructures for selective photoelectrochemical water oxidation or reduction

Nano Lett.

One-dimensional metal-oxide nanostructures: recent developments in synthesis, characterization, and applications

Adv. Funct. Mater.

ZnO-ZnGa2O4 core-shell nanowire array for stable photoelectrochemical water splitting

Nanoscale

Near-field plasmonic functionalization of light harvesting oxide-oxide heterojunctions for efficient solar photoelectrochemical water splitting: the AuNP/ZnFe2O4/ZnO system

Small

High density n-Si/n-TiO2 core/shell nanowire arrays with enhanced photoactivity

Nano Lett.

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Cryst. Growth Des.