Deciphering Sodium-Ion Storage: 2D-Sulfide versus Oxide Through Experimental and Computational Analyses.

Transition metal derivatives exhibit high theoretical capacity, making them promising anode materials for sodium-ion batteries. Sulfides, known for their superior electrical conductivity compared to oxides, enhance charge transfer, leading to improved electrochemical performance. Here, a hierarchical WS2 micro-flower is synthesized by thermal sulfurization of WO3. Comprising interconnected thin nanosheets, this structure offers increased surface area, facilitating extensive internal surfaces for electrochemical redox reactions. The WS2 micro-flower demonstrates a specific capacity of ≈334 mAh g-1 at 15 mA g-1, nearly three times higher than its oxide counterpart. Further, it shows very stable performance as a high-temperature (65 °C) anode with ≈180 mAh g-1 reversible capacity at 100 mA g-1 current rate. Post-cycling analysis confirms unchanged morphology, highlighting the structural stability and robustness of WS2. DFT calculations show that the electronic bandgap in both WS2 and WO3 increases when going from the bulk to monolayers. Na adsorption calculations show that Na atoms bind strongly in WO3 with a higher energy diffusion barrier when compared to WS2, corroborating the experimental findings. This study presents a significant insight into electrode material selection for sodium-ion storage applications.

Enhancing Photoelectrochemical Water Oxidation on WO3 via Electrochromic Modulation: Universal Effects and Mechanistic Insights.

Although WO3 exhibits both electrochromic and photoelectrochemical (PEC) properties, there is no research conducted to investigate the correlation between them. The study herein reports the electrochromic enhancement of PEC activity on WO3. The electrochromic WO3 (e-WO3) exhibits a significantly enhanced activity for PEC water oxidation compared to raw WO3 (r-WO3), with a limiting photocurrent density three times that of r-WO3. The electrochromic enhancement of PEC activity is universal and independent of the type of cations inserted during electrochromism. Decoloring reduces the PEC activity but a simple re-coloring restores the activity to its maximum value. Electrochromism induces large amounts of oxygen vacancies and surface states, the former improving the electron density of WO3 and the latter facilitating the hole transfer across e-WO3/electrolyte interface. It is proved that the electrochromic enhancement effect is due to the significantly improved electron-hole separation efficiency and the charge transfer efficiency across the WO3/electrolyte interface.

Laser-Printed Photoanode: Femtosecond Laser-Induced Crystalline Phase Transformation of WO3 Nanorods for Space-Efficient and Flexible Thin-Film Solar Water-Splitting Cells.

Despite its potential for clean hydrogen harvesting, photoelectrochemical (PEC) water-splitting cells face challenges in commercialization, particularly related its harvesting performance and productivity at an industrial scale. Herein, a facile fabrication method of flexible thin-film photoanode for PEC water-splitting to overcome these limitations, based on laser processing technologies, is proposed. Laser-induced graphene, a carbon structure produced through direct laser writing carbonization (DLWC), plays a dual role: a flexible and stable current collector and a substrate for the hydrothermal synthesis of tungsten trioxide (WO3) nanorods (NRs). To facilitate water-splitting, a femtosecond-pulsed laser (fs laser) is focused on the WO3 NRs, converting their crystalline phase from pristine orthorhombic to monoclinic structure without thermal damage. With NiFe layered double hydroxide (LDH) catalyst, the flexible thin-film photoanode exhibits good PEC performance (1.46 mA cm-2 at 1.23 VRHE) and retains ≈90% of its performance after 3000 bending cycles. With its excellent mechanical properties, the flexible photoanode can be operated in various shapes with different curvatures, enabling space-efficient PEC water-splitting by loading larger photoanode within a given space. This study is expected to contribute to the advancement of large-scale solar water-splitting cells, introducing a new approach to enhance H2/O2 production and expand its application range.

Defect Engineering of WO3 by Rapid Flame Reduction for Efficient Photoelectrochemical Conversion of Methane into Liquid Oxygenates.

Photoelectrochemical (PEC) conversion is a promising way to use methane (CH4) as a chemical building block without harsh conditions. However, the PEC conversion of CH4 to value-added chemicals remains challenging due to the thermodynamically favorable overoxidation of CH4. Here, we report WO3 nanotube (NT) photoelectrocatalysts for PEC CH4 conversion with high liquid product selectivity through defect engineering. By tuning the flame reduction treatment, we carefully controlled the oxygen vacancies of WO3 NTs. The optimally reduced WO3 NTs suppressed overoxidation of CH4 showing a high total C1 liquid selectivity of 69.4% and a production rate of 0.174 µmol cm-2 h-1. Scanning electrochemical microscopy revealed that oxygen vacancies can restrain the production of hydroxyl radicals, which, in excess, could further oxidize C1 intermediates to CO2. Additionally, band diagram analysis and computational studies elucidated that oxygen vacancies thermodynamically suppress overoxidation. This work introduces a strategy for understanding and controlling the selectivity of photoelectrocatalysts for direct conversion of CH4 to liquids.

Nanoparticulated WO3/NiWO4 Using Cellulose as a Template and Its Application as an Auxiliary Co-Catalyst to Pt for Ethanol and Glycerol Electro-Oxidation.

This work reports the use of cellulose as a template to prepare nanosized WO3 or NiWO4 and its application as a co-catalyst in the electro-oxidation of ethanol and glycerol. Microcrystalline cellulose was hydrolyzed with phosphotungstic acid (H3PW12O40) to prepare the nanocrystalline cellulose template. The latter was air-calcinated to remove the template and obtain nanometric WO3. Tungsten oxide was impregnated with Ni(NO3)2, which was subsequently air-calcinated to obtain the nanometric NiWO4. Elemental analysis confirmed the coexistence of nickel and tungsten, whereas thermal analysis evidenced a high thermal stability for these materials. The X-ray diffractograms displayed crystal facets of WO3 and, when Ni(II) was added, NiWO4. The transmission electron micrographs corroborated the formation of nanosized particles with average particle sizes in the range of 30 to 50 nm. Finally, to apply this material, Pt/WO3-C and Pt/WO3-NiWO4-C were prepared and used in ethanol and glycerol electro-oxidation in an alkaline medium, observing a promotional effect of the oxide and tungstate by reducing the onset potential and increasing the current density. These materials show great potential to produce clean electricity or green hydrogen, contributing to energetic transition.

Characterization of WO3/Silicone Rubber Composites for Hydrogen-Sensitive Gasochromic Application.

WO3 and silicone rubber (SR)-based gasochromic composites were fabricated to detect hydrogen leaks at room temperature. WO3 rod-like nanostructures were uniformly distributed in the SR matrix, with a particle size of 60-100 nm. The hydrogen permeability of these composites reached 1.77 cm3·cm/cm2·s·cmHg. At a 10% hydrogen concentration, the visible light reflectance of the composite decreased 49% during about 40 s, with a color change rate of 6.4% s-1. Moreover, the composite detected hydrogen concentrations as low as 0.1%. And a color scale was obtained for easily assessing hydrogen concentrations in the environment based on the color of composites. Finally, the composite materials as disposable sensors underwent testing at several Sinopec hydrogen refueling stations.

Cs-Doped WO3 with Enhanced Conduction Band for Efficient Photocatalytic Oxygen Evolution Reaction Driven by Long-Wavelength Visible Light.

Cesium doped WO3 (Cs-WO3) photocatalyst with high and stable oxidation activity was successfully synthesized by a one-step hydrothermal method using Cs2CO3 as the doped metal ion source and tungstic acid (H2WO4) as the tungsten source. A series of analytical characterization tools and oxygen precipitation activity tests were used to compare the effects of different additions of Cs2CO3 on the crystal structure and microscopic morphologies. The UV-visible diffuse reflectance spectra (DRS) of Cs-doped material exhibited a significant red shift in the absorption edge with new shoulders appearing at 440-520 nm. The formation of an oxygen vacancy was confirmed in Cs-WO3 by the EPR signal, which can effectively regulate the electronic structure of the catalyst surface and contribute to improving the activity of the oxygen evolution reaction (OER). The photocatalytic OER results showed that the Cs-WO3-0.1 exhibited the optimal oxygen precipitation activity, reaching 58.28 µmol at 6 h, which was greater than six times higher than that of WO3-0 (9.76 µmol). It can be attributed to the synergistic effect of the increase in the conduction band position of Cs-WO3-0.1 (0.11 V) and oxygen vacancies compared to WO3-0, which accelerate the electron conduction rate and slow down the rapid compounding of photogenerated electrons-holes, improving the water-catalytic oxygen precipitation activity of WO3.

Electronic Structure Engineering of Pt Species over Pt/WO3 toward Highly Efficient Electrocatalytic Hydrogen Evolution.

Pt-based supported materials, a widely used electrocatalyst for hydrogen evolution reaction (HER), often experience unavoidable electron loss, resulting in a mismatching of electronic structure and HER behavior. Here, a Pt/WO3 catalyst consisting of Pt species strongly coupled with defective WO3 polycrystalline nanorods is rationally designed. The electronic structure engineering of Pt sites on WO3 can be systematically regulated, and so that the optimal electron-rich Pt sites on Pt/WO3 -600 present an excellent HER activity with only 8 mV overpotential at 10 mA cm-2 . Particularly, the mass activity reaches 7015 mA mg-1 at the overpotential of 50 mV, up to 26-fold higher than that of the commercial Pt/C. The combination of experimental and theoretical results demonstrates that the O vacancies of WO3 effectively mitigate the tendency of electron transfer from Pt sites to WO3 , so that the d-band center could reach an appropriate level relative to Fermi level, endowing it with a suitable Δ G H ∗ $\Delta {G_{{{\rm{H}}^ * }}}$ . This work identifies the influence of the electronic structure on catalytic activity.

Point-of-care diagnostics for rapid determination of prostate cancer biomarker sarcosine: application of disposable potentiometric sensor based on oxide-conductive polymer nanocomposite.

One of the most important reasons for an increased mortality rate of cancer is late diagnosis. Point-of-care (POC) diagnostic sensors can provide rapid and cost-effective diagnosis and monitoring of cancer biomarkers. Portable, disposable, and sensitive sarcosine solid-contact ion-selective potentiometric sensors (SC-ISEs) were fabricated as POC analyzers for the rapid determination of the prostate cancer biomarker sarcosine. Tungsten trioxide nanoparticles (WO3 NPs), polyaniline nanoparticles (PANI NPs), and PANI-WO3 nanocomposite were used as ion-to-electron transducers on screen-printed sensors. WO3 NPs and PANI-WO3 nanocomposite have not been investigated before as ion-to-electron transducer layers in potentiometric SC sensors. The designated sensors were characterized using SEM, XRD, FTIR, UV-VIS spectroscopy, and EIS. The inclusion of WO3 and PANI in SC sensors enhanced the transduction at the interface between the screen-printed SC and the ion-selective membrane, offering lower potential drift, a longer lifetime, shorter response time, and better sensitivity. The proposed sarcosine sensors exhibited Nernstian slopes over linear response ranges 10-3-10-7 M, 10-3-10-8 M, 10-5-10-9 M, and 10-7-10-12 M for control, WO3 NPs, PANI NPs, and PANI-WO3 nanocomposite-based sensors, respectively. From a comparative point of view between the four sensors, PANI-WO3 nanocomposite inclusion offered the lowest potential drift (0.5 mV h-1), the longest lifetime (4 months), and the best LOD (9.95 × 10-13 M). The proposed sensors were successfully applied to determine sarcosine as a potential prostate cancer biomarker in urine without prior sample treatment steps. The WHO ASSURED criteria for point-of-care diagnostics are met by the proposed sensors.

A review of tungsten trioxide (WO3)-based materials for antibiotics removal via photocatalysis.

Antibiotics are extensively used in human medicine and animal breeding. The use of antibiotics has posed significant risks and challenges to the natural water environment. On a global scale, antibiotics have been frequently detected in the environment, azithromycin (254-529 ng·L-1), ciprofloxacin (245-1149 ng·L-1), ofloxacin (518-1998 ng·L-1), sulfamethoxazole (1325-5053 ng·L-1), and tetracycline (31.4-561 ng·L-1) are the most detected antibiotics in wastewater and surface water. Abuses of antibiotics has caused a significant threat to water resources and has seriously threatened the survival of human beings. Therefore, there is an urgent need to reduce antibiotic pollution and improve the environment. Researchers have been trying to develop effective methods and technologies for antibiotic degradation in water. Finding efficient and energy-saving methods for treating water pollutants has become an important global topic. Photocatalytic technology can effectively remove highly toxic, low-concentration, and difficult-to-treat pollutants, and tungsten trioxide (WO3) is an extremely potential alternative catalyst. Pt/WO3 photocatalytic degradation efficiency of tetracycline was 72.82%, While Cu-WO3 photocatalytic degradation efficiency of tetracycline was 96.8%; WO3/g-C3N4 photocatalytic degradation efficiency of ceftiofur was 70%, WO3/W photocatalytic degradation efficiency of florfenicol was 99.7%; WO3/CdWO4 photocatalytic degradation efficiency of ciprofloxacin was 93.4%; WO3/Ag photocatalytic degradation efficiency of sulfanilamide was 96.2%. Compared to other water purification methods, photocatalytic technology is non-toxic and ensures complete degradation through a stable reaction process, making it an ideal water treatment method. Here, we summarize the performance and corresponding principles of tungsten trioxide-based materials as a photocatalytic catalyst and provide substantial insight for further improving the photocatalytic potential of WO3-based materials.

High Selectivity Hydrogen Gas Sensor Based on WO3/Pd-AlGaN/GaN HEMTs.

We investigated the hydrogen gas sensors based on AlGaN/GaN high electron mobility transistors (HEMTs) for high temperature sensing operation. The gate area of the sensor was functionalized using a 10 nm Pd catalyst layer for hydrogen gas sensing. A thin WO3 layer was deposited on top of the Pd layer to enhance the sensor selectivity toward hydrogen gas. At 200 °C, the sensor exhibited high sensitivity of 658% toward 4%-H2, while exhibiting only a little interaction with NO2, CH4, CO2, NH3, and H2S. From 150 °C to 250 °C, the 10 ppm hydrogen response of the sensor was at least eight times larger than other target gases. These results showed that this sensor is suitable for H2 detection in a complex gas environment at a high temperature.

Controllable Synthesis of N2-Intercalated WO3 Nanorod Photoanode Harvesting a Wide Range of Visible Light for Photoelectrochemical Water Oxidation.

A highly efficient visible-light-driven photoanode, N2-intercalated tungsten trioxide (WO3) nanorod, has been controllably synthesized by using the dual role of hydrazine (N2H4), which functioned simultaneously as a structure directing agent and as a nitrogen source for N2 intercalation. The SEM results indicated that the controllable formation of WO3 nanorod by changing the amount of N2H4. The ß values of lattice parameters of the monoclinic phase and the lattice volume changed significantly with the nW: nN2H4 ratio. This is consistent with the addition of N2H4 dependence of the N content, clarifying the intercalation of N2 in the WO3 lattice. The UV-visible diffuse reflectance spectra (DRS) of N2-intercalated exhibited a significant redshift in the absorption edge with new shoulders appearing at 470-600 nm, which became more intense as the nW:nN2H4 ratio increased from 1:1.2 and then decreased up to 1:5 through the maximum at 1:2.5. This addition of N2H4 dependence is consistent with the case of the N contents. This suggests that N2 intercalating into the WO3 lattice is responsible for the considerable red shift in the absorption edge, with a new shoulder appearing at 470-600 nm owing to formation of an intra-bandgap above the VB edges and a dopant energy level below the CB of WO3. The N2 intercalated WO3 photoanode generated a photoanodic current under visible light irradiation below 530 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO3 doing so below 470 nm. The high incident photon-to-current conversion efficiency (IPCE) of the WO3-2.5 photoanode is due to efficient electron transport through the WO3 nanorod film.

Facet Engineering on WO3 Mono-Particle-Layer Electrode for Photoelectrochemical Water Splitting.

Photoelectrochemical (PEC) performance of WO3 photoanodes for water splitting is heavily influenced by the orientation of crystal facets. In this work, mono-particle-layer electrodes, assembled by particulate WO3 square plates with highly uniform alignment along the (002) facet, improved PEC water oxidation kinetics and stability. Photo-deposition of Au along the cracks formed on the surface of the plates, which are the edges of {110} facets, was found to further enhance electron collection efficiency. Combination of these two strategies allowed the facet-engineered WO3 electrode to produce significantly higher efficiencies in charge separation and transfer than the electrode prepared without facet orientation. This work has provided a facile route for fabricating a structurally designed WO3 photoelectrode, which is also applicable to other regularly shaped semiconductor photocatalysts with anisotropic charge migration.

Electrochromic Inorganic Nanostructures with High Chromaticity and Superior Brightness.

The possibility of actively controlling structural colors has recently attracted a lot of attention, in particular for new types of reflective displays (electronic paper). However, it has proven challenging to achieve good image quality in such devices, mainly because many subpixels are necessary and the semitransparent counter electrodes lower the total reflectance. Here we present an inorganic electrochromic nanostructure based on tungsten trioxide, gold, and a thin platinum mirror. The platinum reflector provides a wide color range and makes it possible to "reverse" the device design so that electrolyte and counter electrode can be placed behind the nanostructures with respect to the viewer. Importantly, this makes it possible to maintain high reflectance regardless of how the electrochemical cell is constructed. We show that our nanostructures clearly outperform the latest commercial color e-reader in terms of both color range and brightness.

Iridium in Tungsten Trioxide Matrix as an Efficient Bi-Functional Electrocatalyst for Overall Water Splitting in Acidic Media.

Electrocatalytic water splitting in acidic media is a promising strategy for grid scale production of hydrogen using renewable energy, but challenges still exist in the development of advanced catalysts with both high activity and stability. Herein, it is reported that iridium doped tungsten trioxide (Ir-doped WO3 ) with arrayed structure and confined Ir sites is an efficient and durable bi-functional catalyst for overall acidic water splitting. A low overpotential (258 mV) is required to achieve an oxygen evolution reaction current density of 10 mA cm-2 in 0.5 m H2 SO4 solution. Meanwhile, Ir-doped WO3 processes a similar intrinsic activity to Pt/C toward hydrogen evolution reaction. Overall water splitting using the bi-functional Ir-doped WO3 catalyst shows low cell voltages of 1.56 and 1.68 V to drive the current densities of 10 and 100 mA cm-2 , respectively, with only 16 mV decay observed after 60 h continuous electrolysis under the current density of 100 mA cm-2 . Structural analysis and density functional theory calculation indicate that the adjusted coordination environment of Ir within the crystalline matrix of WO3 contributes to the high activity and durability.

Ultrasensitive ppb-level trimethylamine gas sensor based on p-n heterojunction of Co3O4/WO3.

Trace poisonous and harmful gases in the air have been harming and affecting people's health for a long time. At present, effective and accurate detection of ppb-level harmful gas is still a bottleneck to be overcome. Herein, we report a ppb-level triethylamine (TEA) gas sensor based on p-n heterojunction of Co3O4/WO3, which is prepared with ZIF-67 as the precursor and provides Co3O4deposited tungsten oxide flower-like structure. Due to the introduction of Co3O4and the 3D flower-like structure of WO3, the Co3O4/WO3-2 gas sensor shows excellent gas sensing performance (1101 for 10 ppm at 240 °C), superb selectivity, good long-term stability and linear response for TEA concentration. Moreover, the experimental results indicate that the Co3O4/WO3-2 gas sensor also possesses a good response to 50 ppb TEA, in fact, the theoretical limit of detection is 0.6 ppb. Co3O4not only improves the efficiency of electron separation/transport, but also accelerates the oxidation rate of TEA. This method of synthesizing p-n heterojunction with ZIF as the precursor provides a new idea and method for the preparation of low detection limit gas sensors.

Degradation of carbamazepine by UVA/WO3/hypochlorite process: Kinetic modelling, water matrix effects, and density functional theory calculations.

The rapid recombination of electron/hole pairs is a major setback in the application of WO3-based photocatalysis in water treatment. In this study, hypochlorite (ClO-) was used as an electron acceptor to enhance the photocatalytic degradation of carbamazepine (CBZ) using UVA-excited WO3. The results showed that CBZ degradation in the UVA/WO3/ClO- system followed a pseudo-first order reaction kinetic model. The addition of 0.1 mM ClO- to the UVA/WO3 system at pH values of 8.2 and 6.2 increased the rate constant (kobs) of the degradation process 5.3- and 11.5-fold, respectively. Further, increasing the WO3 dosage or decreasing the initial CBZ concentration resulted in an increase in kobs. However, at high concentrations, ClO- inhibited CBZ degradation. Based on the kinetic model, it could be suggested that ClO played a dominant role in the degradation process. Furthermore, the water matrix effects were as follows: the optimal pH was 6.2; humic acid, chloride, bicarbonate, and ammonium exhibited inhibitory effects on CBZ degradation; and sulfate ion significantly enhanced the degradation. Density functional theory (DFT) calculations indicated a strong affinity between ClO- and the WO3 surface. Specifically, the electrical energy per order that was associated with the use of ClO- varied in the range of 0.100-1.617 kWh/m3. In summary, this study shows that ClO- is an excellent electron acceptor for excited WO3, while clarifying the CBZ degradation-enhancing effect of ClO- as well as the kinetic model and DFT calculations. These findings can be employed in the degradation of recalcitrant contaminants in a cost-effective manner, while being significant for the development of more effective catalysts of UV-assisted advanced oxidation processes.

Evaluating the Response Time of an Optical Gas Sensor Based on Gasochromic Nanostructures.

We propose a method for determining complex dielectric permittivity dynamics in the gasochromic oxides in the course of their interaction with a gas as well as for estimating the diffusion coefficient into a gasochromic oxide layer. The method is based on analysis of a time evolution of reflection spectra measured in the Kretschmann configuration. The method is demonstrated with a hydrogen-sensitive trilayer including an Au plasmonic film, WO3 gasochromic oxide layer, and Pt catalyst. Angular dependences of the reflectance as well as transmission spectra of the trilayer were measured in series at a constant flow of gas mixtures with hydrogen concentrations in a range of 0-0.36%, and a detection limit below 40 ppm (0.004%) of H2 was demonstrated. Response times to hydrogen were found in different ways. We show that the dielectric permittivity dynamics of WO3 must be retrieved in order to correctly evaluate the response time, whereas a direct evaluation from intensity changes for chosen wavelengths may have a high discrepancy. The proposed method gives insight into the optical properties dynamics for sensing elements based on gasochromic nanostructures.

Effect of (100) and (001) Hexagonal WO3 Faceting on Isoprene and Acetone Gas Selectivity.

The hexagonal WO3 polymorph, h-WO3, has attracted attention due to its interatomic channels, allowing for a greater degree of intercalation compared to other WO3 polymorphs. Our research group has previously demonstrated h-WO3 to be a highly sensitive gas sensing material for a flu biomarker, isoprene. In this work, the gas sensing performance of this polymorph has been further investigated in two distinct configurations of the material produced by different processing routes. The first sample was synthesized using Na2WO4·2H2O and showed (100) faceting. The second sample was synthesized using WCl6 and showed (001) faceting. The gas sensing response of the nanostructured films deposited using the (100) textured h-WO3 sample 1 had a higher response to acetone at 350 °C. The (001) textured h-WO3 sample 2 favored isoprene at 350 °C. The selectivity of the latter to isoprene is explained in terms of the dangling bonds present on the (001) facets. The tungsten and oxygen dangling bonds present on the (001) plane favor the adsorption of the isoprene molecule over that of the acetone molecule due to the oxygen containing dipole present in the acetone molecule.

Full-Color-Tunable Nanophotonic Device Using Electrochromic Tungsten Trioxide Thin Film.

Color generation based on strategically designed plasmonic nanostructures is a promising approach for display applications with unprecedented high-resolution. However, it is disadvantageous in that the optical response is fixed once the structure is determined. Therefore, obtaining high modulation depth with reversible optical properties while maintaining its fixed nanostructure is a great challenge in nanophotonics. In this work, dynamic color tuning and switching using tungsten trioxide (WO3), a representative electrochromic material, are demonstrated with reflection-type and transmission-type optical devices. Thin WO3 films incorporated in simple stacked configurations undergo dynamic color change by the adjustment of their dielectric constant through the electrochromic principle. A large resonance wavelength shift up to 107 nm under an electrochemical bias of 3.2 V could be achieved by the reflection-type device. For the transmission-type device, on/off switchable color pixels with improved purity are demonstrated of which transmittance is modulated by up to 4.04:1.