Porous WO3 Research Articles

Charge transfer and recombination kinetics at WO3 for photoelectrochemical water oxidation

The photoelectrochemical properties of nanostructured, porous WO3 films deposited by screen printing have been characterized by steady-state and small signal modulation methods as a function of film thickness. Monoclinic WO3 with a wide particle size distribution between 50 and 500 nm was synthesized by a very simple method, via the dehydration of tungstic acid. Related to the open morphology and relatively large feature sizes, the optimal thickness for light harvesting and current collection is about 12 μm for front-side and about 20 μm for backside illumination. Intensity-modulated photocurrent spectroscopy (IMPS) shows that the rate constant for charge transfer to the electrolyte solution is larger than that for surface recombination in most of the applied potential range, illustrating the promise of the material. However, charge collection is found to be an important process that can limit the photocurrent, especially for thicker electrodes in the photocurrent onset potential region.

A low cost preparation of WO3 nanospheres film with improved thermal stability of gasochromic and its application in smart windows

Porous WO3 nanospheres film was successfully synthesized by employing a low-cost and facile template-assisted sol–gel method. The effects of template agent (Pluronic F127) on structure, morphology and specific surface area were systematically studied by Fourier transform infrared (FTIR), x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N2 physisorption. It was found that F127 played a significant role in governing the morphology of WO3 sol clusters, and the optimal post-processing for ‘naked’ WO3 nanospheres film is acetone extraction and subsequent annealing treatment at 350 °C. As anticipated, the relative fast coloring/bleaching rates of WO3 nanospheres film are believed to be the results of porous microstructure and nanocrystalline, where provides much surface active position (166 m2 g−1) and shortens the proton diffusion distance. We believe that this unique approach to synthesize nanospheres structure may has beneficial effects on applications which also are based on insertion/extraction and diffusion abilities, such as supercapacitor, batteries and gas sensors.

Facile Preparation of Porous WO3 Film for Photoelectrochemical Splitting of Natural Seawater

Sunlight-driven natural seawater splitting provides a promising way for large-scale conversion and storage of solar energy. Here, we develop a facile and low-cost method via a deposition–annealing technique to fabricate porous WO3 film and demonstrate its application as a photoanode for natural seawater splitting. The WO3 film yields a photocurrent density of 1.95 mA cm−2 and possesses excellent stability at 1.23 V (versus RHE), under the illumination of 100 mW cm−2 (AM 1.5G). The photoelectrochemical performance is ascribed to the large surface area and good permeation of the electrolyte into the porous film. Furthermore, the photocurrent density remains almost the same during 3 h continuous light irradiation. The evolution of chlorine gas from seawater splitting was determined with qualitative and quantitative analyses, with a Faradic efficiency of about 56%.

Nano-structured WO3 layers sensitized with ALD Pt for quick detection of H2S

WO3 nano-structured layers on top of micro-hotplates were formed by sol–gel deposition technique and electrochemical anodic etching of thin tungsten layers. Both types of gas sensing layers were activated by drop coated Pt nano-particles and alternatively, by atomic layer deposited (ALD) Pt. Due to the limited number of ALD cycles the Pt layer is not a contiguous but composed of uniformly distributed nano-particles of 2–3 nm size. Devices were characterized by their responses for exposure of H2S and NH3. Investigation of sensitivity, selectivity and device dynamics revealed that the ALD sensitized, electrochemically formed porous WO3 layer is suitable for quick detection of H2S.

Formation of Subsurface W5+ Species in Gasochromic Pt/WO3 Thin Films Exposed to Hydrogen

M/WO3 (M = Pt, Pd) systems formed by a porous WO3 thin film decorated by metal nanoparticles are known for their reversible coloring upon exposure to H2 at room temperature. In this work, this gasochromic behavior is investigated in situ by means of near-ambient photoemission (NAPP). Pt/WO3 systems formed by very small Pt nanoparticles (10 ± 1 nm average size) incorporated in the pores of nanocolumnar WO3 thin films prepared by magnetron sputtering at an oblique angle have been exposed to a small pressure of hydrogen at ambient temperature. The recorded UV–vis transmission spectra showed the reversible appearance of a very intense absorption band responsible for the blue coloration of these gasochromic films. In an equivalent experiment carried out in the NAPP spectrometer, W 4f, O 1s, Pt 4f, and valence band photoemission spectra have been recorded at various photon energies to follow the evolution of the reduced tungsten species and hydroxyl groups formed upon film exposure to hydrogen. The obtained res...

Large-Scale Tunable 3D Self-Supporting WO3 Micro-Nano Architectures as Direct Photoanodes for Efficient Photoelectrochemical Water Splitting.

Hydrogen production from water based on photoelectrochemical (PEC) reactions is feasible to solve the urgent energy crisis. Herein, hierarchical 3D self-supporting WO3 micro-nano architectures in situ grown on W plates are successfully fabricated via ultrafast laser processing hybrid with thermal oxidation. Owing to the large surface area and efficient interface charge transfer, the W plate with hierarchical porous WO3 nanoparticle aggregates has been directly employed as the photoanode for excellent PEC performance, which exhibits a high photocurrent density of 1.2 mA cm-2 at 1.0 V vs Ag/AgCl (1.23 V vs RHE) under AM 1.5 G illumination and reveals excellent structural stability during long-term PEC water splitting reactions. The nanoscale and microscale features can be facilely tuned by controlling the laser processing parameters and the thermal oxidation conditions to achieve improved PEC activity. The presented hybrid method is simple, cost-effective, and controllable for large-scale fabrication, which should provide a new and general route that how the properties of conventional metal oxides can be improved via hierarchical 3D micro-nano configurations.

Combinatorial synthesis and high-throughput characterization of structural and photoelectrochemical properties of Fe:WO3 nanostructured libraries

Porous and photoelectrochemically active Fe-doped WO3 nanostructures were obtained by a combinatorial dealloying method. Two types of precursor materials libraries, exhibiting dense and nano-columnar morphology were fabricated by using two distinct magnetron sputter deposition geometries. Both libraries were subjected to combinatorial dealloying enabling preparation and screening of a large quantity of compositions having different nanostructures. This approach allows identifying materials with interesting photoelectrochemical characteristics. The dealloying process selectively dissolved Fe from the composition gradient precursor W–Fe materials library, resulting in formation of monoclinic single crystalline nanoblade-like structures over the entire surface. Photoelectrochemical properties of nanostructured Fe:WO3 films were found to be composition-dependent. The measurement region doped with ∼1.7 at % Fe and a film thickness of ∼ 900–1100 nm displayed highly porous WO3 nanostructures and exhibited the highest photocurrent density of ∼ 72 μA cm−2. This enhanced photocurrent density is attributed to the decreased bandgap values, suppressed recombination of electron–hole pairs, improved light absorption as well as efficient charge transport in the highly porous Fe-doped film with single crystalline WO3 nanoblades.

Efficient removal of Cs+ and Sr2+ from aqueous solution using hierarchically structured hexagonal tungsten trioxide coated Fe3O4

Efficient, irreversible capture of radioactive strontium and cesium from aqueous media remains a serious task for nuclear waste disposal and environmental protection. To address this task, an effective sorbent based on magnetic composites coated with the synthetic porous exchanger WO3 was prepared by a facile method and characterized in detail. XRD analysis indicated that the WO3 coating did not change the phase of the Fe3O4 core, and TEM imaging further showed that Fe3O4@WO3 particles were successfully obtained with nearly uniform size. A batch of experiments was carried out to investigate the efficiency of Fe3O4@WO3 in removing Sr2+ and Cs+ under various environmental conditions. Experimental results showed that Fe3O4@WO3 has higher adsorption capacity for Sr2+ and Cs+ in acidic aqueous solution in comparison to the previous literature. The theoretical maximum adsorption capacities of Fe3O4@WO3 for Sr2+ and Cs+ are 44.178 and 53.175mgg−1, respectively, as modeled by Langmuir isotherms. The adsorption process is fast and reaches equilibrium within 3h, which is attributed to the good dispersion of WO3 on the surface of Fe3O4 and provided much more adsorption sites. Other than Ca2+ and K+, coexisting electrolyte ions had no significant competition effects on the removal of Sr2+ and Cs+ by Fe3O4@WO3. In addition, the Fe3O4@WO3 adsorbent remains stable in acidic solutions and may be repeatedly used 5 times without any noticeable loss in adsorption capacity; the used adsorbents can be easily separated from the aqueous solution using a magnetic method. The advantages of being nontoxic, highly stable, and resistant to acid, as well as having high adsorption capacity for Sr2+ and Cs+, indicate that Fe3O4@WO3 has significant potential for real radioactive wastewater treatment.

Hierarchically solvothermal synthesis of WO3-based nanocomposite: Nature-inspired structure and enhanced gas-sensing property

Composed of the heart, cardiac valves and blood vessels, the blood circulation system can manage the aggregation and the movement of the blood regularly and efficiently. Due to the analogical fluidity of the charge carrier and the blood, such system may act as the inspiration to design the advanced gas-sensing material. As a proof-of-concept, firstly, the porous WO3 monomer was synthesized and recombined with the one-dimensional NiO monomer through the P-N junction to construct a similar structure. Subsequently, a series of gas-sensing tests towards the ethanol were measured. The obtained result indicates this nature-inspired nanocomposite indeed shows an enhanced gas-sensing property towards the ethanol, testifying the rationality of our design.

Porous WO3 with Hierarchical Structure on FTO Substrates: Fabrication and Photoelectrochemical Water Oxidation Performance

Porous WO3 with Hierarchical Structure on FTO Substrates: Fabrication and Photoelectrochemical Water Oxidation Performance

Bifunctional porous non-precious metal WO2hexahedral networks as an electrocatalyst for full water splitting

This work describes a non-precious metal-based electrocatalyst that porous WO2hexahedral networks supported on Ni foam possess remarkably electrochemical performance for HER, OER, and full water-splitting by a simple two-step synthesis.

Investigating the Influence of Au Nanoparticles on Porous SiO2–WO3 and WO3 Methanol Transformation Catalysts

Analyzing the structural and chemical properties of materials at the interface of metal nanoparticles and metal oxide supports is important for catalytic applications. Tungsten oxide (WO3) is a widely studied catalyst, but changing the catalytic reactivity at the surface of this oxide with metal nanoparticles is of interest. In this work, we sought to modify the redox properties of porous WO3 and SiO2–WO3 catalysts with sonochemically deposited gold nanoparticles (Au NPs) in order to access and study this reaction pathway. Characterization using powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy (ICP-OES) confirmed that crystalline Au NPs with diameters of 5–12 nm were distributed throughout the catalysts. Temperature-programmed desorption (TPD) was used to probe the surface acidity of the catalysts. The physico-chemical characteristics of catalysts have been also di...

Photoelectrochemical mineralization of emerging contaminants at porous WO3 interfaces

Nanocrystalline WO3 absorbs visible light up to 470nm and generates OH radicals via valence band injection. Therefore, it promotes the OH mediated oxidation of organic pollutants, when applied to the near UV–vis photodegradation of environmentally relevant target molecules like atenolol and carbamazepine. They both represent potentially hazardous recalcitrant contaminants of emerging concern (CEC) in waters. In the case of WO3 electrodes, a considerable acceleration of the degradation kinetics (up to 4–5 times) occurs through the application of a 1.5V potential bias, which is instrumental to optimize the charge separation within the thin films and to maximize holes transfer rate to the electrolyte. Moreover, after sufficiently long irradiation, the complete mineralization of the organics is obtained. Interestingly, the photo-electrochemical degradation process (applied bias condition) maintains its effectiveness and a large efficiency margin over conventional open circuit conditions. Photoelectrocatalysis is observed even in diluted supporting electrolyte conditions, representing the average salinity of natural freshwater samples, demonstrating the advantageous practical feasibility of the photo-electrochemical approach.

Combustion synthesized hierarchically porous WO3 for selective acetone sensing

An easy, inexpensive combustion route was designed to synthesize hierarchically porous WO3. The tungsten source was fresh peroxiotungstic acid by dissolving tungsten powder into hydrogen peroxide. To promote the combustion reaction, a combined fuel of both glycine and hydrazine hydrate was used. The microstructure was well-connected pores comprised of subunit nanoparticles. Upon exposing towards acetone gas, the porous WO3 based sensor exhibits high gas response, rapid response and recovery, and good selectivity in the range of 5–1000 ppm under working temperature of 300 °C. This excellent sensing performance was plausibly attributed to the porous morphology, which hence provides more active sites for the gas molecules' reaction.

Highly enhanced acetone sensing performance of porous C-doped WO3 hollow spheres by carbon spheres as templates

WO3-based gas sensors have received considerable attention in breath acetone analysis for their great potential in the clinical diagnosis of diabetes. However, several key challenges, especially sensitivity, selectivity and stability, should be further addressed before WO3-based materials are capable of applying for acetone analysis. Herein, C-doped WO3 sensing materials were synthesized by coupling carbon sphere templates with post-heat treatment method. The resulting materials are composed mainly of ε-WO3, a phase with high selectivity to acetone, and featured with porous hollow sphere structure. The as-fabricated sensors based on the C-doped WO3 materials show high sensitivity to acetone down to 0.2ppm. By contrast, the sensors show substantially lower response to other gases including ethanol, methanol, toluene, NH3, NO and CO. In addition, the effect of the relative humidity (RH) on the sensing property was studied and it was found that the response distinction to acetone even at 90% RH was sufficient to separate diabetics from healthy people. More attractively, the ε-phase WO3 could maintain its acetone sensing activity at 350°C over 3 months, suggesting excellent long-term stability. The results gained herein may be useful for rational design of new types of highly selective and stable acetone sensing materials.

Photocatalytic activity of electron-deficient and porous WO3 nanoparticles derived from thermal oxidation of bulk WC particles

Abstract Electron-deficient and porous WO 3 particles were prepared by the simple thermal oxidation of commercial bulk WC. The crystal structure of as-prepared WO 3 particles was monoclinic phases and its crystallinity and morphology were controlled by varying the calcination temperature. Small and interconnected WO 3 particles were divided and formed from bulk WC particles with increasing calcination temperature. The electronic structure of thermally oxidized particles was studied by W L III -edge XANES. Interestingly, as-prepared WO 3 samples were in an electron-deficient state (W +6−δ ). The photocatalytic performance of as-prepared samples was investigated in terms of oxygen production in AgNO 3 aqueous solution and decomposition of the organic dye, Rhodamine B. The photoelectrochemical and photocatalytic activity were correlated and the results were most favorable for WO 3 particles thermally oxidized at 700 °C for oxygen production and 600 °C for photocurrent production.

Effect of proton intercalation on photo-activity of WO3 anodes for water splitting

Porous and nanostructured WO3 semiconductor thin films have been used as electrodes for water photo-electrolysis. As water-splitting cells frequently operate in acidic conditions, the aim of this work is to evaluate the effect of proton intercalation of WO3 electrodes on the performance of the photo-electrolysis process. For this, a first study of proton charge and proton discharge electrode's capacity was performed under cathodic and anodic polarization, respectively, at different voltages and times. Protonated electrodes were then exposed to simulated solar radiation in a photo-electrochemical cell (PEC) and characterized with both chronoamperometry and linear sweep voltammetry. The results indicated that proton intercalation reduces WO3 photo-activity; however, the effect is reversible and after enough time full proton discharge is achieved and photoresponse is recovered. The work points out the influence of the WO3 film microstructure on the discharge kinetics and proposes proton intercalation/deintercalation studies as a characterization technique of photoelectrodes.

Characterization and application of a new pH sensor based on magnetron sputtered porous WO3 thin films deposited at oblique angles

In this communication we report about an outstanding solid-state pH sensor based on amorphous nanocolumnar porous thin film electrodes. Transparent WO3 thin films were deposited by reactive magnetron sputtering in an oblique angle configuration to enhance their porosity onto indium tin oxide (ITO) and screen printed electrodes (SPE). The potentiometric pH response of the nanoporous WO3-modified ITO electrode revealed a quasi-Nernstian behaviour, i.e. a linear working range from pH 1 to 12 with a slope of about ⿿57.7mV/pH. pH detection with this electrode was quite reproducible, displayed excellent anti-interference properties and a high stable response that remained unaltered over at least 3 months. Finally, a pH sensor was developed using nanoporous WO3-modified screen printed electrode (SPE) using a polypyrrole-modified Ag/AgCl electrode as internal reference electrode. This full solid state pH sensor presented a Nernstian behaviour with a slope of about ⿿59mV/pH and offered important analytical and operation advantages for decentralized pH measurements in different applications.

Defects in Porous Networks of WO3 Particle Aggregates

AbstractThe most frequently studied functionalities of porous WO3 particle systems—namely their electrochromic and photocatalytic properties—are intimately related to the wanted or unwanted action of defects in the material. Here, we report on the generation and action of three types of defects in WO3 electrodes: solid/solid interfaces between adjacent particle aggregates, defects generated in situ upon photoinduced electron accumulation, and defects resulting from tungsten bronze formation. Depending on the degree of aggregate interconnection, we observe a beneficial, albeit transient, effect of charge accumulation on the photoelectrocatalytic activity of the thin films, giving rise to an almost threefold increase in photocurrent. The dynamic change of thin film properties associated with this doping process is tracked by a combined spectroscopic and electrochemical approach, which allows the beneficial and detrimental effects of defects to be resolved on the electrochemical potential scale.

WO3 Nanofiber-Based Biomarker Detectors Enabled by Protein-Encapsulated Catalyst Self-Assembled on Polystyrene Colloid Templates.

A novel catalyst functionalization method, based on protein-encapsulated metallic nanoparticles (NPs) and their self-assembly on polystyrene (PS) colloid templates, is used to form catalyst-loaded porous WO3 nanofibers (NFs). The metallic NPs, composed of Au, Pd, or Pt, are encapsulated within a protein cage, i.e., apoferritin, to form unagglomerated monodispersed particles with diameters of less than 5 nm. The catalytic NPs maintain their nanoscale size, even following high-temperature heat-treatment during synthesis, which is attributed to the discrete self-assembly of NPs on PS colloid templates. In addition, the PS templates generate open pores on the electrospun WO3 NFs, facilitating gas molecule transport into the sensing layers and promoting active surface reactions. As a result, the Au and Pd NP-loaded porous WO3 NFs show superior sensitivity toward hydrogen sulfide, as evidenced by responses (R(air)/R(gas)) of 11.1 and 43.5 at 350 °C, respectively. These responses represent 1.8- and 7.1-fold improvements compared to that of dense WO3 NFs (R(air)/R(gas) = 6.1). Moreover, Pt NP-loaded porous WO3 NFs exhibit high acetone sensitivity with response of 28.9. These results demonstrate a novel catalyst loading method, in which small NPs are well-dispersed within the pores of WO3 NFs, that is applicable to high sensitivity breath sensors.