Defect Engineering of Air-Treated WO₃ and Its Enhanced Visible-Light-Driven Photocatalytic and Electrochemical Performance

Abstract

In this paper, we reported that oxygen vacancies could be introduced in tungsten oxide hierarchical nanostructures through air treatment at certain temperatures. The production of oxygen vacancies may be due to two mechanisms, i.e., critical phase transition and nanoscale inhomogeneous deformation, depending on the annealing temperature or time and the size of the building block. The oxygen vacancies can be introduced at 300 and 350 °C when critical phase transformation from orthorhombic WO3·0.33H2O to hexagonal WO3 takes place or 350 and 400 °C when nanoscale inhomogeneous deformation occurs in the nanobelts. Moreover, the oxygen vacancy concentration is also influenced by the annealing time. For comparison, the oxygen vacancies are also introduced by hydrogen treatment. It is found that a certain amount of oxygen vacancies introduced by air treatment could trap and transfer electrons, thus decreasing the electron–hole recombination rate and improving the conductivity, while an abundance of oxygen vacancies introduced by hydrogen treatment could facilitate the electron–hole pair recombination and destroy the hexagonal tunnel structure, resulting in lower photocatalytic activity and electrochemical performance. Through air treatment, the constant rate of photocatalytic performance in degrading rhodamine B under visible light irradiation can reach 0.0300 min–1, and the specific capacitance can improve to 166.7 F/g. It is suggested that both photocatalytic activity and electrochemical performance can be greatly improved by introducing a proper concentration of oxygen vacancies through air treatment.

Defects Engineering in Photocatalytic Water Splitting Materials

“…But sometimes it is difficult to distinguish the difference between surface defects and bulk defects. For instance, Zhang and co‐worker have reported the oxygen vacancies of WO 3 introduced by air treatment and employed TEM to study the oxygen vacancies . As shown in Figure a and 9b, the unannealed WO 3 ⋅0.33H 2 O shows a perfect lattice feature, but the edge of the WH−A350 nanorod becomes disordered due to the existence of oxygen vacancies.…”

1D WO3 Nanorods/2D WO3−x Nanoflakes Homojunction Structure for Enhanced Charge Separation and Transfer towards Efficient Photoelectrochemical Performance

“…Li usually fabricated from WO 3 film templates by annealing treatment in reducing atmosphere or etchingi nr educings olution. [18,19] Wang et al [20] introduced oxygen vacancies into WO 3 by hydrogen treatment, and the obtained WO 3Àx exhibited a significantly improved photocurrentd ensity of 0.88 mA cm À2 at 1.0 Vv ersus Ag/AgCl compared with pristineW O 3 (0.1 mA cm À2 at 1.0 Vv s. Ag/AgCl) as ar esult of the increased amount of oxygen vacancies, which can serve as electron donors. However,f ormation of excessive surface oxygen vacancies may occur during this process and lead to the introductiono fc arrier-recombination centers.…”

Enhanced photocatalytic performance of tungsten oxide through tuning exposed facets and introducing oxygen vacancies

“…[31] There are many approaches to introduce oxygen vacancies, such as hydrogen treatment, [34,35] ball milling [36] and air annealing. [37,38] Among them, air annealing through control the annealing temperature and time is a very convenient and effective method for introducing oxygen vacancies.…”