Enhanced photoelectrochemical performance of plate-like WO3 induced by surface oxygen vacancies

https://doi.org/10.1016/j.elecom.2016.05.004Get rights and content

Highlights

  • A plate-like WO3 film with surface oxygen vacancies is fabricated by low temperature processing.

  • The concentration of oxygen vacancies could be controlled by tuning the treatment time in H2O2 solution.

  • Appropriate surface oxygen vacancies could improve light-to-electricity conversion efficiency.

Abstract

The plate-like WO3 photo-electrode with surface oxygen vacancies was fabricated via a H2O2 treatment method for the first time. The concentration of oxygen vacancies could be controlled by tuning the treatment time in H2O2 solution. Under visible light, the WO3 plate anodes with different concentration of surface oxygen vacancies were evaluated for photoelectrochemical water splitting and the optimum photocurrent was about 1.5 times as high as that of pure WO3. This study presents a new insight into improving the light-to-electricity conversion efficiency of WO3 by introducing surface oxygen vacancies.

Introduction

Since the pioneering work by Fujishima and Honda in 1972 [1], extensive efforts have been made to investigate for the photoelectrolysis of water in to H2 and O2 [2], [3], [4]. Among semiconductors, tungsten oxide (WO3) has attracted great interest because of its high stability in acidic conditions and relatively small band gap (2.7 eV) [5], [6], [7], [8]. However, various charge recombination pathways have been identified as a key factor limiting the performance of practical devices.

Enormous efforts have been devoted to improve the WO3 performance in the visible region, including nanotechnology [9], [10], [11], surface modification [12], [13], [14], [15], doping [16], [17], [18], and so on. For example, one-dimensional (1D) and two-dimensional (2D) nanostructures of WO3 (e.g. nanorods [6], [19], [20], nanowire [11] and nanoplate [10], [21], [22], [23], [24]) have the superior ability of promoting the transport and separation of photogenerated charge carriers. Photoelectrodes of WO3 nanoplate, nanowires, nanobelts and nanorod have been fabricated and exhibited enhanced photoelectrochemical (PEC) activity, demonstrating the great potential of such WO3 nanostructures [10], [19], [25].

Furthermore, it is commonly believed that oxygen vacancies play a key role in the properties of WO3 [26]. Substoichiometric WO3  x is formed by creating oxygen vacancies in WO3, which is thermodynamically stable at room temperature [27]. Desai et al. found that the WO3  x could be used as a passive layer to protect tungsten metal from further dissolution in chemical mechanical polishing [28]. Li et al. demonstrated that the donor density of WO3  x was increased three orders of magnitude by introduction of oxygen vacancy, resulting in an order of magnitude enhancement in photocurrent density [7]. However, they got substoichiometric WO3  x by annealing pristine WO3 in hydrogen atmosphere at 350–450 °C.

In this communication, we reported a simple method of introduction of oxygen vacancies into the surface of the plate-like WO3 films. Substoichiometric WO3  x was obtained by hydrogen peroxide (H2O2) treatment, which offers an advantage of low temperature processing. The oxygen vacancies formed in the presence of surface of WO3 demonstrated enhanced PEC performance over pristine WO3 platelet.

Section snippets

Experiment

The plate-like WO3 films were prepared on a fluorine-doped tin oxide (FTO) glass slide using our reported hydrothermal method [10]. Then the films were calcined in air at 450 °C for 1 h with a heating rate of 2 °C/min. The as-prepared WO3 samples were immersed in a 20% H2O2 solution. The solution was kept at 20 °C for a certain time, and then, the films were cleaned with de-ionized water to remove the residual H2O2 solution and dried under vacuum at 80 °C. Scanning electron microscopy (SEM) images

Results and discussion

Hydrothermal method is a novel, low-cost and low-temperature approach to realize the controllable synthesis of vertically oriented WO3 plate-like arrays grown directly on a transparent FTO conductive glass [10], [11]. A uniform film consisting of plate-like nanostructures was obtained after annealing (Fig. 1a). The cross-sectional view image (inset in Fig. 1a) shows that the flakes are tetragonal in shape with height of ca. 1.4 μm and grown vertically on the FTO conductive glass. Fig. 1b–e show

Conclusion

Plate-like WO3 films with surface oxygen vacancies were prepared via a facile economic H2O2 treatment method. The concentration of oxygen vacancies could be controlled by tuning the treatment time in H2O2 solution. The H2O2 treated WO3 photoanodes exhibit an enhanced photoelectrochemical water splitting performance, which is attributed to high separation efficiency of photoinduced electron–hole pairs. The above results show that introducing appropriate surface oxygen vacancies could improve

Conflict of interest

The author's declare that there are no conflicts of interest.

Acknowledgments

We acknowledge the financial support from the NSFC (No. 51304253), and the Fundamental Research Funds for the Central Universities of Central South University (2015zzts021).

References (37)

  • F. Su et al.

    Branched TiO2 nanoarrays sensitized with CdS quantum dots for highly efficient photoelectrochemical water splitting

    Phys. Chem. Chem. Phys.

    (2013)
  • J. Gan et al.

    Oxygen vacancies promoting photoelectrochemical performance of In2O3 nanocubes

    Sci. Rep.

    (2013)
  • S.S. Kalanur et al.

    Facile growth of aligned WO3 nanorods on FTO substrate for enhanced photoanodic water oxidation activity

    J. Mater. Chem. A

    (2013)
  • G. Wang et al.

    Hydrogen-treated WO3 nanoflakes show enhanced photostability

    Energy Environ. Sci.

    (2012)
  • W. Wei et al.

    Rapid anodic formation of high aspect ratio WO3 layers with self-ordered nanochannel geometry and use in photocatalysis

    Chem. Eur. J.

    (2012)
  • Z.-G. Zhao et al.

    Nanoporous-walled tungsten oxide nanotubes as highly active visible-light-driven photocatalysts

    Angew. Chem. Int. Ed.

    (2008)
  • J. Yang et al.

    Hydrothermal synthesis and photoelectrochemical properties of vertically aligned tungsten trioxide (hydrate) plate-like arrays fabricated directly on FTO substrates

    J. Mater. Chem.

    (2012)
  • J. Su et al.

    Vertically aligned WO3 nanowire arrays grown directly on transparent conducting oxide coated glass: synthesis and photoelectrochemical properties

    Nano Lett.

    (2010)
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