ZnWO₄/WO₃ Composite for Improving Photoelectrochemical Water Oxidation

Abstract

A rapid screening technique utilizing a modified scanning electrochemical microscope has been used to screen photocatalysts and determine how metal doping affects its photoelectrochemical (PEC) properties. We now extend this rapid screening to the examination of photocatalyst (semiconductor/semiconductor) composites: by examining a variety of ZnWO 4 /WO 3 composites, a 9% Zn/W ratio produced an increased photocurrent over pristine WO 3 with both UV and visible irradiation on a spot array electrode. With bulk films of various thickness formed by a drop-casting technique of mixed precursors and a one-step annealing process, the 9 atomic % ZnWO 4 /WO 3 resulted in a 2.5-fold increase in the photocurrent compared to pristine WO 3 for both sulfite and water oxidation at +0.7 V vs Ag/AgCl. Thickness optimization of the bulkfilm electrodes showed that the optimum oxide thickness was ∼1 μm for both the WO 3 and ZnWO 4 /WO 3 electrodes. X-ray diffraction showed the composite nature of the WO 3 and ZnWO 4 mixtures. The UV/vis absorbance and PEC action spectra demonstrated that WO 3 has a smaller band gap than ZnWO 4 , while Mott−Schottky analysis determined that ZnWO 4 has a more negative flat-band potential than WO 3 . A composite band diagram was created, showing the possibility of greater electron/hole separation in the composite material. Investigations on layered structures showed that the higher photocurrent was only observed when the ZnWO 4 /WO 3 composite was formed in a single annealing step.

Bio-molecule Assisted Aggregation of ZnWO4 Nanoparticles (NPs) into Chain-like Assemblies: Material for High Performance Supercapacitor and as Catalyst for Benzyl Alcohol Oxidation

“…It is noteworthy that the spectra in both f and g are taken in aqueous solution of ZnWO 4 after sonication for few minutes. We also collected the absorption spectra of the solid ZnWO 4 sample after making a thin film over the glass substrate given as 37 In our case the E g value observed for the samples is 3.29 eV and the shifting of the band gap is attributed to the change in particle shape and size, respectively. The strong self-trapping tendency of the exciton formed via the O 2p hybridized W 5d state for W based semiconductors was reported earlier.…”

General Characterization Methods for Photoelectrochemical Cells for Solar Water Splitting

“…Figure 11 shows Mott-Schottky plots with the straight tangent line to determine the E FB of WO 3 and ZnWO 4 . [70] In addition, the conductivity type (n or pt ype) for as emiconductor can be determined by the sign of the slope of this straightt angent line. Generally, if the slope of the straight tangent line is positive, the semiconductor is nt ype;h owever,i fthes lope is negative, the semiconductor is ptype.…”

Piezoresistive effects enhanced the photocatalytic properties of Cu2O/CuO nanorods

“…Two values of approximately 1.8 eV and 2.2 eV corresponding to the E g of CuO and Cu 2 O, respectively, were extracted. Although this is not a quantitative approach for the sample, it still qualitatively indicates the relative band gap variations for a composite comprising one predominant phase [41]. In addition, because of the tailing effect below the band gaps, which may result from the phonon-assisted or other mechanisms to lead to variations of the band edges [42], the absorption edge of approximately 1.4 eV was ignored, partly because of its moderate slope, compared with the other two edges.…”