Formation Of WO Research Articles

An Enhanced Synaptic Plasticity of Electrolyte-Gated Transistors through the Tungsten Doping of an Oxide Semiconductor

Oxide electrolyte-gated transistors have shown the ability to emulate various synaptic functions, but they still require a high gate voltage to form long-term plasticity. Here, we studied electrolyte-gated transistors based on InOx with tungsten doping (W-InOx). When the tungsten-to-indium ratio increased from 0% to 7.6%, the memory window of the transfer curve increased from 0.2 V to 2 V over a small sweep range of −2 V to 2.5 V. Under 50 pulses with a duty cycle of 2%, the conductance of the transistor increased from 40-fold to 30,000-fold. Furthermore, the W-InOx transistor exhibited improved paired pulse facilitation and successfully passed the Pavlovian test after training. The formation of WO3 within InOx and its ion intercalation into the channel may account for the enhanced synaptic plasticity.

Role of S-Vacancy Concentration in Air Oxidation of WS2 Single Crystals.

Semiconducting transition metal dichalcogenides (TMDs) are a class of two-dimensional materials with potential applications in optoelectronics, spintronics, valleytronics, and quantum information processing. Understanding their stability under ambient conditions is critical for determining their in-air processability during device fabrication and for predicting their long-term device performance stability. While the effects of environmental conditions (i.e., oxygen, moisture, and light) on TMD degradation are well-acknowledged, the role of defects in driving their oxidation remains unclear. We conducted a systematic X-ray photoelectron spectroscopy study on WS2 single crystals with different surface S-vacancy concentrations formed via controlled argon sputtering. Oxidation primarily occurred at defect concentrations ≥ 10%, resulting in stoichiometric WO3 formation, while a stable surface was observed at lower concentrations. Theoretical calculations informed us that single S-vacancies do not spontaneously oxidize, while defect pairing at high vacancy concentrations facilitates O2 dissociation and subsequent oxide formation. Our XPS results also point to vacancy-related structural and electrostatic disorder as the main origin for the p-type characteristics that persists even after oxidation. Despite the complex interplay between defects and TMD oxidation processes, our work unveils scientifically informed guidance for working effectively with TMDs.

Simple synthesis and efficient photocatalytic hydrogen production of WO3-WS2 and WO3–WS2–MoS2

Facile preparation of efficient photocatalysts is one of the challenges to realizing the practical application of photocatalysis technology. In this paper, binary composite WO3-WS2 and ternary composite WO3–WS2–MoS2 were easily prepared through simple one-step acidification-thermal decomposition (abbreviated as AT) of ammonium tetrathiotungstate (ATT) and ammonium tetrathiomolybdate (ATM) just using the inevitable formation of WO3 during the acidification of ATT. Especially, their photocatalytic hydrogen production performances were determined and the reasons for their activity differences were investigated systematically based on XRD, SEM, TEM, and XPS characterizations. The results showed that on the whole, these two composites possess better performance than both pure MoS2 and WS2, as well as our previously reported WO3-WS2 (1637.8 μmol h−1 g−1). Besides, the average hydrogen evolution rate of WO3-WS2 (5998.6 μmol h−1 g−1) is higher than that of WO3–WS2–MoS2 (4907.2 μmol h−1 g−1). Moreover, for the ternary composites, when the content of W and Mo is close, the change in W to Mo ratio has no obvious impact on the hydrogen production performance. Finally, a performance comparison of different preparation methods manifests that the one-step AT method is the simplest and most effective. This work can offer useful guidance for the preparation and photocatalytic application of both WS2 and MoS2-based composites.

Hot Corrosion Behavior of Plasma-Sprayed WC-CoCr Coatings on AISI 316L Steel Substrate in Na2SO4-25% NaCl Salt Environment

This study investigates the hot corrosion resistance characteristics of plasma-sprayed WC-CoCr coatings deposited on AISI 316L stainless steel. Coated and uncoated samples were exposed to a fused Na2SO4-25%NaCl salt deposit at 700 °C in cyclic conditions for fifty thermal cycles. The corrosion kinetics were determined using a thermogravimetric method. To determine the hot corrosion rate, weight-change measurements were taken after every cycle. X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscopy were performed on samples to examine the hot corrosion characteristics. With a fused salt deposit at 700 °C, the uncoated AISI 316L steel substrate samples experienced faster high-temperature oxidation as compared to coated samples. It was noticed that the uncoated steel substrate gained a little weight during the first few cycles, afterwards as the number of thermal cycles increased, the weight gain followed a linear kinetics. The WC-CoCr coating reduced the weight gain of steel substrate by about 75% in a corrosive salt environment. The plasma-sprayed WC-CoCr coatings had adhesion strength and microhardness of 10.8 ± 2.4 MPa and 410 ± 25 HV0.5, respectively. The hot corrosion-affected coatings displayed slow-scaling kinetics. The oxides of the coatings, formed at the surface were rich in chromium and tungsten. These oxides helped in providing hot corrosion resistance in the corrosive environment as they worked as obstacles to the penetration/diffusion of corrosive elements through coatings. The higher content of tungsten inside the coating promoted WO3 formation, which improved resistance to corrosion at elevated temperatures. Chromium in the coating caused the formation of spinel CoCr2O4 and Cr2O3 the spinel CoCr2O4 that emerged as an intermediate phase also contributes to the maintenance of corrosion resistance. Some oxides such as Fe2O3, FeCr2O4, and CoSO4 were found. Apart from that some traces of Na were also found.

Study of the Photocatalytic Activity of Titanium and Tungsten Oxides Obtained by Electric Explosion of Metal Conductors in Air

Oxides as a shape of micro- and nanosized powder, containing agglomerates of particles with a high specific surface, were obtained by means of electric Ti and W wire explosion in the air. An X-ray phase analysis showed that the only product of Ti destruction is TiO2, while the electric explosion of W conductors results in the formation of WO3 + W2O7 mixture, which tungsten anhydride WO3 dominates in, and traces of a residual metallic W come across. The photocatalytic properties of electroexplosive powder were studied using a model oxidation reaction of methylene blue. It was revealed that both TiO2 and the WO3 + W2O7 mixture demonstrate catalytic activity within a wide spectrum of radiation, including the visible one. The catalytic activity of the WO3 + W2O7 mixture under ultraviolet and incandescent lamp radiation was inferior to that of TiO2, however, in the solar radiation, the rate of dye degradation with the participation of tungsten oxides is higher. In this case, the average rate of decreasing concentration of the dye in water containing a mixture of WO3 + W2O7 depends but a little on the type of the radiation source.

Leidenfrost green synthesis method for MoO3 and WO3 nanorods preparation: characterization and methylene blue adsorption ability

Environmental pollution is a critical issue due to its impact on humans and other organisms. An important demand nowadays is the need for a green method to synthesize nanoparticles to remove pollutants. Therefore, this study focuses for the first time on synthesizing the MoO3 and WO3 nanorods using the green and self-assembled Leidenfrost method. The XRD, SEM, BET and FTIR analyses were used to characterize the yield powder. The XRD results emphasize the formation of WO3 and MoO3 in nanoscale with crystallite sizes 46.28 and 53.05 nm and surface area 2.67 and 24.72 m2 g−1, respectively. A comparative study uses synthetic nanorods as adsorbents to adsorb methylene blue (MB) in aqueous solutions. A batch adsorption experiment was performed to investigate the effects of adsorbent doses, shaking time, solution pH and dye concentration to remove MB dye. The results demonstrate that the optimal removal was achieved at pH 2 and 10 with 99% for WO3 and MoO3, respectively. The experimental isothermal data follow Langmuir for both adsorbents with a maximum adsorption capacity of 102.37 and 151.41 mg g−1 for WO3 and MoO3.

Effect of WO3 Nanoparticles on the Radiative Attenuation Properties of SrTiO3 Perovskite Ceramic

In the present work, an experimental study is performed to study the radiation shielding characteristics of SrTiO3 (STO) perovskite ceramic added with different amounts (x = 0, 2, 5, and 10%) of tungsten trioxide nanoparticles (WO3 NPs). The four ceramic samples were prepared using the solid-state reaction method. The structural properties were examined using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. The analysis showed the successful formation of WO3- doped STO samples. The crystallite size, estimated using the Scherrer equation, was found in the range of 50.86–41.17 nm. The effect of WO3 NPs on the radiation shielding performance of these ceramics was studied. Different parameters, such as linear attenuation coefficient (LAC) and other related factors, were experimentally determined. The linear attenuation coefficient results demonstrated that the additional amount of WO3 in the ceramics correlates with an improvement in their shielding abilities. The half-value layer (HVL) values for the ceramics with 2% WO3 nanoparticles are equal to 0.071, 1.760, 2.407, and 2.564 cm at 0.060, 0.662, 1.173, and 1.333 MeV, respectively. As the energy increases, more radiation can pass through the material; therefore, a larger thickness is required to absorb half of the total photons, leading to a greater HVL. The tenth value results reaffirmed that increasing the WO3 content in the STO ceramics improves their shielding efficiency. The radiation protection efficiency (RPE) of the four prepared STO ceramics was reported. From the RPE, we found that more photons can be attenuated at lower energies.

PANI-WO3·2H2O Nanocomposite: Phase Interaction and Evaluation of Electronic Properties by Combined Experimental Techniques and Ab-Initio Calculation.

The development of conjugated polymer-based nanocomposites by adding metallic particles into the polymerization medium allows the proposition of novel materials presenting improved electrical and optical properties. Polyaniline Emeraldine-salt form (ES–PANI) has been extensively studied due to its controllable electrical conductivity and oxidation states. On the other hand, tungsten oxide (WO3) and its di-hydrated phases, such as WO3·2H2O, have been reported as important materials in photocatalysis and sensors. Herein, the WO3·2H2O phase was directly obtained during the in-situ polymerization of aniline hydrochloride from metallic tungsten (W), allowing the formation of hybrid nanocomposites based on its full oxidation into WO3·2H2O. The developed ES–PANI–WO3·2H2O nanocomposites were successfully characterized using experimental techniques combined with Density Functional Theory (DFT). The formation of WO3·2H2O was clearly verified after two hours of synthesis (PW2 nanocomposite), allowing the confirmation of purely physical interaction between matrix and reinforcement. As a result, increased electrical conductivity was verified in the PW2 nanocomposite: the DFT calculations revealed a charge transfer from the p-orbitals of the polymeric phase to the d-orbitals of the oxide phase, resulting in higher conductivity when compared to the pure ES–PANI.

Mechanical properties and oxidation behavior of CrWSiN films

In this study, CrWSiN films were fabricated through direct current magnetron cosputtering, and the sputtering power applied to the target was selected as the process variable. In addition, the mechanical properties and oxidation resistance of CrWSiN films with Si contents of 9–10 and 15–18 at.% were evaluated and compared with those of CrSiN and WSiN films. Among the aforementioned films, crystalline Cr21W28Si9N42 films exhibited the highest hardness of 25.0 GPa and highest Young's modulus of 323 GPa because they contained W. The formation of oxide species in the CrWSiN films after annealing at 800 °C in ambient air was affected by the films' chemical compositions. W-enriched CrWSiN films exhibited low oxidation resistance because of the formation of WO3. However, the oxidation resistance of the Cr21W28Si9N42 films was higher than that of the W-enriched films. This improvement was achieved through the formation of a Cr2WO6 surface oxide layer above the WO3 oxide layer. Moreover, a Cr2O3 surface layer and an amorphous SiOx interface formed on the W-depleted films, which restricted their subsequent oxidation.

Effect of W on the thermal stability, mechanical properties and corrosion resistance of Fe-based bulk metallic glass

In this work, the effect of refractory metal W on the thermal stability, mechanical properties and corrosion resistance of Fe36Cr23Mo18-XWXC15B6Y2 (X = 0, 3, 5, 8, 10, 12, 15, 18) bulk metallic glasses (BMGs) were systematically investigated. The results showed that a wide composition range could be quenched to form BMG when the considerable refractory metal was introduced, although the higher mixing enthalpy of W than Mo between other elements (such as Fe, Cr, C) incited the deterioration of glass forming ability (GFA). The introduction of W significantly improved the thermal stability of the alloy system with glass transition temperature Tg and onset crystallization temperature Tx of Fe36Cr23Mo8W10C15B6Y2 BMG reached 923 K and 972 K, respectively. The W-bearing Fe-based BMGs also exhibited a very high hardness of 1400 HV and Young's modulus of 271 GPa, respectively. The extremely high thermal stability and elastic modulus were mainly derived from the strong chemical bonding between atoms. In addition, the large addition of W reduced the corrosion current density of the original alloy by an order of magnitude, which was mainly due to the formation of WO3 and the increase of MoO2 in the passivation film which inhibit the pit initiation and pit growth.

Tailoring pulsed laser deposition of phosphorus doped WOx films from (PO2)4(WO3)4 target by space-resolved optical emission spectroscopy.

Phosphorus doped WOx films were deposited on fused silica substrates from a target of monophosphate tungsten bronze (PO2)4(WO3)2 m with m = 2. Different conditions of O2 pressures and substrate temperature depositions were performed in parallel to plasma investigations during the depositions step. Changes were observed in the film stoichiometries affecting the film properties while the increase of the O2 pressure. Optical bandgap was shifted from 3.39 eV to 3.86 eV as a function of the deposition pressure from 7.5 Pa to 20 Pa. In situ optical emission spectroscopy was carried out in all the O2 atmosphere conditions. With an increase in the oxygen pressure to 5 Pa, a change in the spectral composition of the plasma with a deficit of the phosphorus lines was observed. A complex plasma containing atoms and multiple ionized ions attributed to each composing species was observed at high O2 pressures of deposition. The increase in O2 pressure led to strong thermalization of the plasma and strong scattering of the plasma particle which created a favourable environment for the WO3 formation.

Yttria-Coated Tungsten Fibers for Use in Tungsten Fiber-Reinforced Composites: A Comparative Study on PVD vs. CVD Routes

Tungsten fiber-reinforced tungsten (Wf/W) composites are being developed to improve the intrinsic brittleness of tungsten. In these composites, engineered fiber/matrix interfaces are crucial in order to realize toughening mechanisms. For such a purpose, yttria (Y2O3), being one of the suitable interface materials, could be realized through different coating techniques. In this study, the deposition of thin films of yttria on a 150 µm tungsten wire by physical and chemical vapor deposition (PVD and CVD) techniques is comparatively investigated. Although fabrication of yttria is feasible through both CVD and PVD routes, certain coating conditions such as temperature, growth rate, oxidation of Wf, etc., decide the qualitative nature of a coating to a particular extent. In the case of PVD, the oxidation of Wf is highly reduced compared to the WO3 formation in high-temperature CVD coating processes. Yttria-coated tungsten fibers are examined comprehensively to characterize their microstructure, phase, and chemical composition using SEM, XRD, and Raman spectroscopy techniques, respectively.

Facile synthesis and efficient photoelectrochemical reaction of WO3/WS2 core@shell nanorods utilizing WO3∙0.33H2O phase

One-dimensional (1D) WO3/two-dimensional (2D) WS2 heterojunction nanostructures are of great interest in various photoelectrochemical (PEC) and electrochemical applications. In this study, we introduced a simple and effective route to synthesize 2D WS2 shell layer on WO3 nanorods by utilizing WO3∙0.33H2O phase. The formation of WO3∙0.33H2O nanorods was critically affected by hydrothermal reaction temperature. The WO3∙0.33H2O phase was preferentially transformed into hexagonal WO3 and 2D WS2 through oxidation and sulfurization at 450 °C, respectively. The 2D WS2 shell layer was more favorably formed on WO3 nanorods, which were synthesized at 180 °C and possessed a significant amount of WO3∙0.33H2O phase (referred to as W-180), than on WO3 nanorods with predominant monoclinic WO3 phase, which were synthesized at 200 °C (referred to as W-200). Thus, the WO3/WS2 core@shell nanorods from W-180 exhibited significantly enhanced PEC performance because of the improved charge transfer properties attributed to the advantageous heterojunction effect of 1D WO3/2D WS2. The new synthesis route from WO3∙0.33H2O phase to 2D WS2 can be applied to synthesize various WO3/2D WS2 heterojunction nanostructures, such as thin films, nanoparticles, and nanorods.

Sol-Gel coated WO3 thin films based complementary electrochromic smart windows

The WO3 films were prepared via sol- gel dip coating method. The optical, structural, morphological, electrochemical and electrochromic properties of the prepared films were studied. The WO3 film coated on glass substrate exhibits 74% transmission at 550 nm. XRD studies indicate the WO3 films in the amorphous state. FTIR spectrum confirms the formation of WO3. The FESEM image confirms the formation of smooth surface. The cyclic voltammetric study reveals the anodic/cathodic diffusion coefficients of 2.31/4.79 × 10−12 cm2/s for WO3 films. The film thickness was about 260 nm. The same film shows a change in optical transmission of 55.37% at 550 nm. The sol–gel coated WO3 films were used to develop the complementary electrochromic smart windows in conjugation with NiO and Ni0.95Co0.05O as an anode. A five layered EC windows were developed and studied with Li+ and H+ conducting gel electrolytes.

Tuning Structural Properties of WO3 Thin Films for Photoelectrocatalytic Water Oxidation

The preparation of tungsten oxide (WO3) thin film by direct current (DC) reactive sputtering magnetron method and its photoelectrocatalytic properties for water oxidation reaction are investigated using ultraviolet-visible radiation. The structural, morphological, and compositional properties of WO3 are fine-tuned by controlling thin film deposition time, and post-annealing temperature and environment. The findings suggest that the band gap of WO3 can be controlled by adjusting the post-annealing temperature; the band gap decreased from 3.2 to 2.7 eV by increasing the annealing temperature from 100 to 600 °C. The theoretical calculations of the WO3 bandgap and the density of state are performed by density functional theory (DFT). Following the band gap modification, the photoelectrocatalytic activity increased and the maximum photocurrent (0.9 mA/cm2 at 0.6 VSCE) is recorded with WO3 film heated at 500 °C. The WO3 film heated under air exhibits much better performance in photoelectrochemical water oxidation process than that of annealed under inert atmosphere, due to its structural variation. The change in sputtering time leads to the formation of WO3 with varying film thickness, and the maximum photocurrent is observed when the film thickness is approximately 150 nm. The electrical conductivity and charge transfer resistance are measured and correlated to the properties and the performance of the WO3 photoelectrodes. In addition, the WO3 photoelectrode exhibits excellent photoelectrochemical stability.

PHOTOELECTROCHEMICAL PROPERTIES OF FILMS BASED ON BISMUTH AND COPPER VANADATES

Films of bismuth and nickel tungstates were obtained by chemical and electrochemical synthesis. Bismuth tungstate was obtained by ionic layering and electrochemical deposition. Nickel tungstate (NiWO4) was obtained by combined synthesis methods: 1st - electrochemical synthesis and 2nd - combined electrochemical and thermochemical synthesis. The obtained materials have good adhesion with an optically transparent SnO2 substrate. It is shown that the mechanism of electrochemical formation of Bi2WO6 and NiWO4 films is similar to the processes of WO3 formation as a result of electroreduction of peroxide-complex compounds based on tungstate ions, which were studied in detail in. From the data of coloring kinetics the speed, efficiency and stability of electrochromic material depending on its cycling time are estimated. It is shown that tungstates can cycle for a long time with galvanostatic current change and different potentials. Comparison of electrochromic properties of nickel and bismuth tungstate films obtained by ionic stratification, electrodeposition and combined electrochemical and thermochemical methods showed that polycrystalline films have a lower color contrast compared to films obtained by electrodeposition. Using X-ray phase analysis, it was found that the structure of the obtained materials depended on the method of production. Comparison of X-ray diffraction data for chemically and electrochemically obtained Bi2WO6 showed that the films obtained by electrochemical deposition have more amorphous structure, possibly with inclusions of orthorhombic Bi2WO6 and hexagonal WO3 crystallites, while the films obtained by ionic layering have a layer of polycrystals, indicates the fine-grained obtained crystallites. The studied properties of Bi2WO6 and NiWO4 meet the requirements for electrochromic materials in terms of providing high color contrast in the visible part of the spectrum.

Novel p-type Ag-WO3 nano-composite for low-cost electronics, photocatalysis, and sensing: synthesis, characterization, and application

Semiconductor–metal nanocomposites provide a simple and convenient way to tailor the properties of semiconductors and promote various properties and photoinduced processes like photovoltaic, photo-sensing, and photocatalysis. This article provides a detailed study on the facile synthesis and structural, optical, and electrical characterization of novel p-type silver-tungsten oxide (Ag-WO3) nanocomposite using co-precipitation technique. Results indicate that it has an indirect bandgap of 2.9 eV and possesses excellent charge separation capability, as established by photoluminescence and impedance spectroscopy analysis. TEM and AFM results show the formation of WO3 nano-plates with side length ranging from 10 nm to 25 nm, with the presence of silver nanoparticles (dimension 10–12 nm) either at its center or at the edges. P-type conductivity in the synthesized composite is investigated using PL analysis, which revealed that silver serves as a deep acceptor with acceptor level 1.4 eV above the valance band. To further demonstrate the capability of synthesized Ag-WO3 in electronics, the current–voltage graph of Ag-WO3/Ag Schottky junction with knee voltage 0.59 V is also summarized, which suggest that Ag-WO3 is an effective p-type semiconductor for electronic application too. This study provides new insight into the fabrication and practical application of Ag-WO3 nanocomposite to produce efficient low cost electronic, sensing, and photocatalytic devices.

(Invited) (NH4)2WS4 precursors for Electrochromic Devices

In this research, we investigate the effect of metal doping on the electrochromic (EC) performance of tungsten trioxide (WO3) films. These films were prepared by a novel method involving solution processing and thermal annealing. In this procedure, ammonium tetrathiotungstate ((NH4)2WS4) was dissolved in dimethylformamide at a high concentration ratio (200 mg/mL) to obtain a homogeneous solution and then spin-coated onto the indium thin oxide (ITO) substrate for use as a working electrode. Subsequently, the film was annealed at the different temperatures (200, 300, 400, and 500 oC) to form a crystal structure of WO3. X-ray diffraction, Raman, and X-ray photoelectron spectroscopic results confirm the crystal formation of WO3. Moreover, in order to improve the electrochromic performance, different concentrations (10, 20, 30, and 40 mM) of different metal chlorides such as PtCl4, PdCl2, AuCl3, AgCl, CuCl2, NiCl2, NaCl, and KCl were added into the (NH4)2WS4 precursor and the mixture was coated on the ITO substrate and annealed at 500 oC. The results indicate that the performance of the Au-doped WO3 film was better than those with other dopants, likely as a result of the plasmonic effect. Furthermore, nanocrystal quantum dots (QDs) provide tunable optoelectronic properties on the basis of their dimension. CdSe QDs, which are size-dependent colloidal nanocrystals, are used for efficient electrochromic devices owing to their unique properties in modulating quantum confinement, resulting in enhanced electron insertion during the electrochromic process. Incorporating a well-known metal oxide electrochromic material such as WO3 into CdSe QDs enhances the redox process. Herein, we propose a facile method for producing and optimizing CdSe QDs doped in WO3. The fabrication of the electrochromic film involves a solution and annealing process. Moreover, the effect of the QD size to optimize the electrochromic layer is studied. As a result, the coloration efficiency of WO3 and optimized CdSe QD-WO3 are obtained as 68.6 and 112.3 cm2/C, respectively. Thus, size-tunable nanocrystal QDs combined with a metal oxide yield high-performance electrochromic devices and are promising candidates for producing smart windows. Acknowledgement This research was supported in part by a Creative Materials Discovery Program through the NRF funded by Ministry of Science and ICT (2017M3D1A1039379) and in part by the Basic Research Laboratory of the NRF funded by the Korean government (2018R1A4A1022647).

Starch bio-template synthesis of W-doped CeO2 catalyst for selective catalytic reduction of NOx with NH3: influence of ignition temperature.

A novel tungsten-doped CeO2 catalyst was fabricated via the sweet potato starch bio-template spread self-combustion (SSC) method to secure a high NH3-SCR activity. The study focuses on the influence of ignition temperature on the physical structure and redox properties of the synthesized catalyst and the catalytic performance of NOx reduction with NH3. These were quantitatively examined by conducting TG-DSC measurements of the starch gel, XRD analysis for the crystallites, SEM and TEM assessments for the morphology of the catalyst, XPS and H2-TPR measurements for the distribution of cerium and tungsten, and NH3-TPD assessments for the acidity of the catalyst. It is found that the ignition temperature shows an important role in the interaction of cerium and tungsten species, and the optimal ignition temperature is 500 °C. The increase of ignition temperature from 150 °C is beneficial to the interactions of species in the catalyst, depresses the formation of WO3, and refines the cubic CeO2 crystallite. The sample ignited at 500 °C shows the biggest BET surface area, the highest surface concentration of Ce species and molar ratio of Ce3+/(Ce3++Ce4+), and the most abundant surface Brønsted acid sites, which are the possible reasons for the superiority of the NH3-SCR activity. With a high GHSV of 200,000 mL (g h)-1 and the optimal ignition temperature, Ce4W2Oz-500 can achieve a steadily high NOx reduction of 80% or more at a lowered reduction temperature in the range of 250~500 °C.

WO3 homojunction photoanode: Integrating the advantages of WO3 different facets for efficient water oxidation

Abstract The manipulation of the surface property of WO3 photoanode is the main breakthrough direction to improve its solar water oxidation performance both in thermodynamics and kinetics. Here, we report a WO3(002)/m-WO3 homojunction film that is composed of an upper WO3 layer with predominant (002) facet (WO3(002)) and a lower WO3 layer with multi-crystal facets (m-WO3) as a photoanode for solar water oxidation. Due to the synergistic effect of WO3(002) layer and m-WO3 layer, better water oxidation activity and stability are achieved on the WO3(002)/m-WO3 homojunction film relative to the m-WO3 and WO3(002) film. Specifically, the improved water oxidation performance on the WO3(002)/m-WO3 homojunction film is attributed to the followings. In thermodynamics, the band position differences between WO3(002) layer and m-WO3 layer lead to the formation of WO3(002)/m-WO3 homojunction, which has positive function of improving their charge separation and transfer. In kinetics, the upper WO3(002) layer of the WO3(002)/m-WO3 film has superior activity in the adsorption and activation of water molecules, water oxidation on this homojunction film photoanode is inclined to follow the four-holes pathway, and the corrosion of photoanode from the H2O2 intermediate is restrained. The present work provides a new strategy to modify the WO3 photoanodes for thermodynamically and kinetically efficient water oxidation.