The core–shell nature of nanostructured WO3 photoelectrodes demonstrated in spectroelectrochemical studies (original) (raw)
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Electrochimica Acta, 2010
With the aim of improving the performance and extending the range of applications of mesoporous WO 3 films, which were initially developed for the photoelectrochemical oxidation of water, we investigated the effect of a number of dopants (lithium, silicon, ruthenium, molybdenum and tin) upon the transparency, crystallinity, porosity and conductivity of the modified films. Tin, molybdenum and silicon were shown to improve the electrochromic behaviour of the layers whereas ruthenium enhanced considerably the electronic conductivity of the WO 3 films. Interestingly, most of the dopants also affected the film morphology and the size of WO 3 nanocrystals. X-ray photoelectron spectra revealed absence of significant segregation of doping elements within the film. Raman analyses confirmed that the monoclinic structure of WO 3 films does not change upon substitutional cation doping; thus, the crystallinity of WO 3 films is maintained.
Photoelectrochemical properties of WO3 thin films prepared by electrodeposition
2013
Tungsten trioxide (WO 3 ) thin films were synthesised by electrodeposition using peroxotungtic acid as the precursor electrolyte solution for use as photoanodes in a photoelectrochemical cell for solar hydrogen applications. The films were coated at deposition potentials varying from 0.30 to 0.90 V versus Ag/AgCl in order to study the effect of the potential on the mineralogical, morphological, optical, and photoelectrochemical properties of the nanoparticulate films.
Electrochimica Acta, 2017
WO 3 films have been obtained by anodization of tungsten in the different acidic electrolytes (HCl, H 2 SO 4 , H 3 PO 4 , H 3 PO 4 + NH 4 F) and at various applied potentials. Electrochemical impedance spectroscopy was used to investigate film formation and to characterize the obtained oxide films. The equivalent electric circuits modelling reactive and blocking behaviour are provided and discussed. It was found, that oxide film capacitance decreases linearly with increasing anodization potential. The relative permittivity of tungsten oxide films varies from 31 to 56 depending on the acid used. A relatively high rate of the film formation (1.87 nm V-1) and increased resistance against oxide breakdown can be achieved for tungsten oxide obtained from 0.3 M oxalic acid bath. Compact oxide films are formed at the potentials ranged from 10 V to 30 V, whereas increasing of anodization voltage to 60 V resulted in the formation of disordered, porous structures due to surface etching. Semiconductor properties were determined by Mott-Schottky analysis. Photoelectrochemical properties of as-deposited and annealed at 600°C WO 3 films were determined in a Na 2 SO 4 solution under pulsed and constant UV irradiation. It was determined that annealed WO 3 films in comparison to as-deposited films are more stable and generate substantially higher photelectrochemical currents.
Chemphyschem, 2006
Nanostructured tungsten trioxide thin-film electrodes are prepared on conducting glass substrates by either potentiostatic electrodeposition from aqueous solutions of peroxotungstic acid or direct deposition of WO3 slurries. Once treated thermally in air at 450 °C, the electrodes are found to be composed of monoclinic WO3 grains with a particle size around 30–40 nm. The photoelectrochemical behavior of these electrodes in 1 M HClO4 apparently reveals a low degree of electron–hole recombination. Upon addition of formic acid, the electrode showed the current multiplication phenomenon together with a shift of the photocurrent onset potential toward less positive values. Photoelectrochemical experiments devised on the basis of a kinetic model reported recently [I. Mora-Seró, T. Lana-Villarreal, J. Bisquert, A. Pitarch, R. Gómez, P. Salvador, J. Phys. Chem. B2005, 109, 3371] showed that an interfacial mechanism of inelastic, direct hole transfer takes place in the photooxidation of formic acid. This behavior is attributed to the tendency of formic acid molecules to be specifically adsorbed on the WO3 nanoparticles, as evidenced by attenuated total reflection infrared spectroscopy.
Journal of Physics: Conference Series, 2007
The structural (Raman spectroscopy), electrical (Current-Voltage analysis) and photoelectrical (Photoconduction analysis) properties of the tungsten trioxide films annealed in air at different temperature are reported. The influence of the thermal post-treatment on the morphology of the films and the role of oxygen vacancies on the WO 3 opto-electronic properties has been discussed and linked with possible applications in hydrogen production in a PECC.
Applied Sciences, 2022
Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 prov...
Nano Energy, 2016
WO 3 nanoplate arrays with (002) oriented facets grown on fluorine doped SnO 2 (FTO) glass substrates are tailored by tuning the precursor solution via a facile hydrothermal method. A 2-step hydrothermal method leads to the preferential growth of WO 3 film with enriched (002) facets, which exhibits extraordinary photoelectrochemical (PEC) performance with a remarkable photocurrent density of 3.7 mA cm-2 at 1.23 V vs. revisable hydrogen electrode (RHE) under AM 1.5 G illumination without the use of any cocatalyst, corresponding to ~93% of the theoretical photocurrent of WO 3. Density functional theory (DFT) calculations together with experimental studies reveal that the enhanced photocatalytic activity and better photostability of the WO 3 films are attributed to the synergistic effect of highly reactive (002) facet 2 and nanoplate structure which facilitates the photo-induced charge carrier separation and suppresses the formation of peroxo-species. Without the use of oxygen evolution cocatalysts, the excellent PEC performance, demonstrated in this work, by simply tuning crystal facets and nanostructure of pristine WO 3 films may open up new opportunities in designing high performance photoanodes for PEC water splitting.
RSC Advances, 2014
We report on the surface interaction between NH 3 and WO 3 nanoparticles having different exposed surfaces or different porous structure, to identify the relative importance of exposed crystal surfaces, porous architecture, and specific surface area in the oxide sensing properties. WO 3 nanocrystals with tailored morphology and definite prominent surfaces were synthesized by hydrothermal reactions. In parallel, inverted opal macroporous WO 3 films have been prepared by a one-step sol-gel procedure, and WO 3 hierarchical layers have been obtained by an innovative one-step dual-templating strategy which leads to macropores and mesopores simultaneously. The performances of WO 3 samples in NH 3 sensing, indicate that high-energy surfaces result in a significant improvement of the electrical response. Enhanced porous structure and high surface area are not enough to produce high electrical response, while their synergistic combination with tailored crystal faceting appears effective. XPS survey performed on shape controlled WO 3 nanocrystals demonstrated that, upon interaction with NH 3 , oxidized nitrogen atoms represent the prevalent species on the surface of rectangular (WO 3-RE) nanocrystals with highly exposed high-energy {020} and {002} facets. Conversely, in the case of rectangular platelets (WO 3-SS) and square platelets (WO 3-RS) with very low surface area of high-energy surfaces, N-H surface groups are predominant. These results suggest that {020} and {002} crystal surfaces provide privileged reactive sites for ammonia oxidation and therefore they play a key role in driving the sensing properties of the WO 3 layers.
Solar Energy Materials and Solar Cells, 2010
Different chemical routes for obtaining nanostructured WO 3 on transparent conductive oxides have been tried by considering the Santato-Augustynski recipe as a main guideline. The preparation started from tungstate salts as precursors and involved different organic dispersing agents. Calcination in air at 550 1C produced the final oxide. Aim of this work is to test the oxide materials as photoanodes for the photo-electrochemical water splitting. WO 3 is a wide bandgap semiconductor, able to transport photogenerated carriers under irradiation, provided that it has a good crystalline structure. The morphology and the crystal size of the obtained WO 3 nanoparticles have been investigated by SEM and XRD. This work shows that the particle size of the WO 3 film decreases with increase in molecular weight of the organic dispersing agents. The current-voltage characteristic curves of WO 3 -based electrodes have been obtained by biasing a photo-electrochemical cell with an external voltage ramp, both in the dark and under simulated solar irradiation. Results showed that under incident irradiance a noticeable photocurrent density is obtained with a reasonably steep current-voltage slope and with a plateau current of the order of 1.6-1.8 mA/cm 2 under incident 0.14 W/cm 2 AM 1.5 irradiation.