Bare WO3 Research Articles

BiOI/WO3 photoanode with enhanced photoelectrochemical water splitting activity

This work reports on a novel BiOI/WO3 composite photoanode, which was fabricated by depositing BiOI onto a WO3 nanoflake electrode through a electrodeposition method. The photoelectrochemical (PEC) activity of the BiOI/WO3 electrode for water splitting under visible-light irradiation was evaluated. The results show that the BiOI/WO3 photoanode achieved a photocurrent density of 1.21 mA·cm–2 at 1.23 V vs. reversible hydrogen electrode (RHE), which was higher than that of the bare WO3 nanoflake electrode (0.67 mA·cm–2). The enhanced PEC acticity of BiOI/WO3 for water splitting can be attributed to the expansion of light absorption range as well as the facilitated separation of photo-generated carriers.

Designed growth of WO3/PEDOT core/shell hybrid nanorod arrays with modulated electrochromic properties

Designed growth of tungsten oxide (WO3)/poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell hybrid nanorod arrays has been obtained by combining solvothermal and in situ electropolymerization techniques. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and Raman characterization results indicate that the hybrid nanorods are composed of single crystalline WO3 nanocores wrapped by thin amorphous PEDOT nanoshells. The hybrid nanorods exhibit promising electrochromic performance of much shorter response time (3.8 s for coloring and 3.6 s for bleaching) than the bare WO3 nanorods (12.4 s for coloring and 7.6 s for bleaching), while the optical contrast of the hybrid nanorods increases from 26% of PEDOT to 72% in 633 nm. And the coloring efficiency and stability of the core/shell hybrid nanorods are also enhanced compared to the individual components. Dynamic analysis suggests a synergistic effect between the WO3 nanocore and the PEDOT nanoshell. In addition, color depth and optical contrast of the hybrid nanorods can be modulated by adjusting the applied voltage and the deposition of the PEDOT nanoshell. The hybrid nanorod films obtained by the cost-effective wet chemical methods may find promising applications in energy-saving windows, smart displays as well as other energy efficient technologies.

Mesoporous reduced graphene oxide/WSe2 composite particles for efficient sodium-ion batteries and hydrogen evolution reactions

Mesoporous WSe2-reduced graphene oxide (WSe2-rGO) composite particles were prepared by spray pyrolysis and subsequent selenization. The WSe2-rGO composite particles had both well-dispersed rGO nanosheets and well-faceted WSe2 nanocrystals with plenty of folded edges. As a comparison sample, hierarchical structured WSe2 particles were produced by selenization of the bare WO3 particles obtained by spray pyrolysis. The WSe2-rGO composite particles showed superior electrochemical properties for sodium-ion batteries (SIBs) and electrocatalytic efficiencies for hydrogen evolution reactions (HERs) compared to those of the bare WSe2 particles. The discharge capacities of the WSe2-rGO composite particles and bare WSe2 particles for the 100th cycle at a current density of 0.5 A g−1 for sodium-ion storage were 238 and 36 mA h g−1, respectively; their corresponding capacity retentions measured from the third cycle were 80% and 13%. The WSe2–rGO composite particles showed much lower onset potential and larger current density (36.5 mA cm−2 at η = 300 mV) than those of the bare WSe2 particles (0.61 mA cm−2 at η = 300 mV). The Tafel slopes for the WSe2–rGO composite and bare WSe2 particles were approximately 60 and 115 mV dec−1, respectively.

Conformal BiVO4-Layer/WO3-Nanoplate-Array Heterojunction Photoanode Modified with Cobalt Phosphate Cocatalyst for Significantly Enhanced Photoelectrochemical Performances

Constructing semiconductor heterojunctions via surface/interface engineering is an effective way to enhance the charge carrier separation/transport ability and thus the photoelectrochemical (PEC) properties of a photoelectrode. Herein, we report a conformal BiVO4-layer/WO3-nanoplate-array heterojunction photoanode modified with cobalt phosphate (Co-Pi) as oxygen evolution cocatalyst (OEC) for significant enhancement in PEC performances. The BiVO4/WO3 nanocomposite is fabricated by coating a thin conformal BiVO4 layer on the surface of presynthesized WO3 nanoplate arrays (NPAs) via stepwise spin-coating, and the decoration of Co-Pi OEC is realized by photoassisted electrodeposition method. The optimized Co-Pi@BiVO4/WO3 heterojunction photoanode shows a maximum photocurrent of 1.8 mA/cm2 at 1.23 V vs RHE in a phosphate buffer electrolyte under an AM1.5G solar simulator, which is 5 and 12 times higher than those of bare WO3 and BiVO4 photoanode, respectively. Measurements of UV-vis absorption spectra, electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra reveal that the enhanced PEC performances can be attributed to the increased charge carrier separation/transport benefited from the type II nature of BiVO4/WO3 heterojunction and the promoted water oxidation kinetics and photostability owing to the decoration of Co-Pi cocatalyst.

Isolated Platinum Atoms Stabilized by Amorphous Tungstenic Acid: Metal-Support Interaction for Synergistic Oxygen Activation.

Oxygen activation plays a crucial role in many important chemical reactions such as oxidation of organic compounds and oxygen reduction. For developing highly active materials for oxygen activation, herein, we report an atomically dispersed Pt on WO3 nanoplates stabilized by in situ formed amorphous H2 WO4 out-layer and the mechanism for activating molecular oxygen. Experimental and theoretical studies demonstrate that the isolated Pt atoms coordinated with oxygen atoms from [WO6 ] and water of H2 WO4 , consequently leading to optimized surface electronic configuration and strong metal-support interaction (SMSI). In exemplified reactions of butanone oxidation sensing and oxygen reduction, the atomic Pt/WO3 hybrid exhibits superior activity than those of Pt nanoclusters/WO3 and bare WO3 as well as enhanced long-term durability. This work will provide insight into the origin of activity and stability for atomically dispersed materials, thus promoting the development of highly efficient and durable single atom-based catalysts.

Isolated Platinum Atoms Stabilized by Amorphous Tungstenic Acid: Metal–Support Interaction for Synergistic Oxygen Activation

AbstractOxygen activation plays a crucial role in many important chemical reactions such as oxidation of organic compounds and oxygen reduction. For developing highly active materials for oxygen activation, herein, we report an atomically dispersed Pt on WO3 nanoplates stabilized by in situ formed amorphous H2WO4 out‐layer and the mechanism for activating molecular oxygen. Experimental and theoretical studies demonstrate that the isolated Pt atoms coordinated with oxygen atoms from [WO6] and water of H2WO4, consequently leading to optimized surface electronic configuration and strong metal–support interaction (SMSI). In exemplified reactions of butanone oxidation sensing and oxygen reduction, the atomic Pt/WO3 hybrid exhibits superior activity than those of Pt nanoclusters/WO3 and bare WO3 as well as enhanced long‐term durability. This work will provide insight into the origin of activity and stability for atomically dispersed materials, thus promoting the development of highly efficient and durable single atom‐based catalysts.

Enhanced photoelectrochemical water oxidation on WO3 nanoflake films by coupling with amorphous TiO2

High surface states induced photoelectrochemical (PEC) activity and stability issue is the major performance bottleneck for nanostructured WO3 photoanode. Here we report that amorphous TiO2 (α-TiO2) be used as passivator to modify the surface states of WO3 nanoflakes film for improving its PEC water oxidation performance. In comparison with bare WO3 film, the α-TiO2-coupled WO3 (α-TiO2/WO3) film is of higher PEC water oxidation activity and stability. The photocurrent on α-TiO2/WO3 film photoanode is improved by 2 times that reached 1.4 mA/cm2 in 0.1 M Na2SO4 solution at 0.8 V (vs. SCE). After α-TiO2 coupling, the UV–vis absorption edge and intensity of WO3 film do not change obviously, but the formation and oxidation kinetics of H2O2 on WO3 photoanode are modified. The density functional theory calculations indicate the monoclinic WO3(002) has a surface energy of 1.17 J/m2, whereas the α-TiO2/WO3(002) with a much lower surface energy of 0.3 J/m2. Additionally, the length of TiO bond of α-TiO2 is changed from the initial 1.929 Å to a shorter length of 1.886 Å and a longer length of 2.290 Å in α-TiO2/WO3(002) through the O2--W6+ bonding effect at α-TiO2/WO3 interface. Therefore, the enhanced PEC water oxidation performance on α-TiO2/WO3 film can be attributed to that α-TiO2 passivates the surface states of WO3 nanoflakes film, and the formation of H2O2 from the photoexcited-electrons/dissolved-oxygen route is depressed and the PEC oxidation of H2O2 is accelerated.

Electrochemically-synthesized tungstate nanocomposites γ-WO3/CuWO4 and γ-WO3/NiWO4 thin films with improved band gap and photoactivity for solar-driven photoelectrochemical water oxidation

The main aim of this study was to synthesize and characterise tungstate (WO3) nanocomposites with its metal-based nanostructures, such as copper (II) tungstate (CuWO4) and nickel tungsten oxide (NiWO4), as visible-light active thin film photoanodes for solar-driven photoelectrochemical (PEC) water oxidation. FE-SEM and AFM results showed that the bare as-deposited WO3 films were transformed into polycrystalline WO3 structure with highly agglomerated surfaces and roughness during the annealing-induced crystallisation process. XRD results suggested that the bare as-deposited WO3 films undergone phase transformation process from amorphous to the photoactive monoclinic-I (γ-WO3) at 550 °C. XPS results indicated the existence of WO42−, Ni2+ and Cu2+ ions at 35.58 eV, 856 eV and 932.4 eV, respectively. Through the formation of WO3 nanocomposites, the energy band gap was effectively lowered from 2.7 eV (γ-WO3) → 2.3 eV (γ-WO3/CuWO4) → 2.1 eV (γ-WO3/NiWO4) as estimated from the UV–Vis spectra. Finally, the corresponding photoactivity of WO3 nanocomposites was estimated by measuring the photocurrent density and γ-WO3/NiWO4 nanocomposite structure was found to give the highest photocurrent density of 400 μA/cm2 at 1.5 V vs Ag/AgCl (4 M KCl).

Hierarchical hydrated WO3·0.33H2O/graphene composites with improved lithium storage

Based on the tungsten hydrate structure model, we report the strategy to fabricate hierarchically structured WO3·0.33H2O/graphene composites through a facile hydrothermal approach. The structure characteristics, conversion reaction mechanism as well as the electrochemical properties are carefully investigated. The hierarchical architectures assembled by nanorods or nanobricks of about 20 nm thickness combine the advantages of reduced length scale of Li ion diffusion derived from nanosizes and structural stability guaranteed by hierarchical features. In addition, compared with bare WO3·0.33H2O and anhydrous WO3, the WO3·0.33H2O/graphene composites exhibit the optimal performances with high rate capability and good cycle stability, which is attributed to synergistic effects of structural hydration and graphene: providing a more open charge transfer channel, forming a conductive pathway and accommodating the volume change. Such an improved lithium storage performance makes the graphene-based WO3·0.33H2O a promising anode candidate for lithium-ion battery applications.

Remarkably Improved Dispersion Stability and Thermal Conductivity of WO₃-H₂O Suspension by SiO₂ Coating.

The long term dispersion stability for an improved thermal conductivity is a challenging issue that needs to be solved for heat transfer applications. Hence, this research investigated that a thin layer of SiO2 coating (2-5 nm) over WO3 nanostructures (SiO2@WO3) of different shapes exhibit superior dispersion (0.01%) stability for longer duration (∼3 days) as evident by steady zeta potential (-30 ↔ -60.70 mV), no significant change in particle-size (139 ↔ 147 nm) distribution, density (1.001 ↔ 0.988 g/cm3) and refractive index (1.335 ↔ 1.332) etc., are indicator for colloidal stability relative to bare WO3 nanoparticles and bulk SiO2 aqueous suspension which quickly settles down within 1-2 hours after 30 min sonication at 23 °C. Thin Si-OH layer over WO3 surface imparts superior hydrophilicity, larger surface area for effective solute-solvent (SiO2@WO3-H2O) interaction for improved colloidal stability showing no sedimentation and color change of SiO2@WO3 dispersion (0.01%) even after 3 days due to repulsive interaction between negatively charged Si-O- particles. Thereby, thermal conductivity is found to be quite stable (0.631 ↔ 0.618 W/m K) up to 3 days, whereas aqueous suspension of bare WO3 and SiO2 particles quickly settle down and thermal conductivity rapidly decreased to a value of 0.584 W/m K for de-ionized water further indicates the significance of SiO2 coating. Depending on the thickness of SiO2 layer and volume fraction of SiO2@WO3, a maximum of 8-10% increment of thermal conductivity was achieved where anisotropic WO3 displayed always more (∼5%) thermal conductivity than typical spherical nanoparticles.

Enhanced photodegradation of sulfamethoxazole by a novel WO3-CNT composite under visible light irradiation

As one of the emerging environmental issues, the existence of antibiotics in the water bodies is believed to pose threat to not only the environment but also human health. Recently, semiconductor-based photocatalysis has drawn wide attention since it shows great potential in removal of organic pollutants as well as other emerging organic contaminants from aquatic systems. Therefore, in this study, efforts were devoted to fabrication of novel visible light driven heterogeneous photocatalysts to explore their possible applications in photodegradation of antibiotics. Particularly, multi-walled carbon nanotubes (MWCNTs) was selected as co-catalyst to WO3, and three WO3-MWCNTs (WO3-CNT) composites were prepared as photocatalysts, namely WT-2, WT-4 and WT-8. The physical and chemical properties of these obtained WO3-CNT composites were thoroughly characterized by different methods. Simultaneously, sulfamethoxazole (SMX), one of the most widely used antibiotics was chosen as the target pollutant to evaluate the photocatalytic performance of the WO3-CNT composites. The degradation intermediates were analyzed by LC/MS/MS, and subsequently a possible degradation mechanism was proposed. Compared to bare WO3, all three WO3-CNT composites showed notably enhanced photocatalytic activity, demonstrating that they have the potential to be used as effective photocatalysts to degrade sulfonamide class of antibiotics.

Pd-Doped WO3 Nanostructures as Potential Glucose Sensor with Insight from Electronic Structure Simulations.

Herein, we report the results of crystal-structure-dependent nonenzymatic glucose-sensing properties of tungsten oxide (WO3) and Pd-doped WO3 nanostructures. The WO3 nanomaterials with orthorhombic, monoclinic, and mixed (ortho + monoclinic) phases were harvested by a facile hydrothermal route by varying the reaction time and subsequent annealing processes. Electrocatalytic activity tests of WO3 samples revealed a 3-fold oxidation peak current enhancement in the monoclinic Pd-doped WO3 nanobricks assembly as compared to the orthorhombic WO3 microspheres. Moreover, the Pd-doped WO3 showed a higher glucose-sensing performance in terms of the detection sensitivities of 11.4 μA μM-1 cm-2 (linear range: 5-55 μM) and 5.6 μA μM-1 cm-2 (linear range: 65-375 μM). We have also performed density functional theory simulations for the monoclinic WO3 and Pd-doped WO3 to investigate the charge-transfer and bonding mechanism of glucose on WO3 and Pd-doped WO3 surface. As the binding energy of glucose is higher in the case of Pd-doped WO3 as compared to bare WO3, it becomes more conducting due to enhancement of density of states near Fermi level; theoretically, we can predict that Pd-doped WO3 exhibits a better charge-transfer media compared to bare WO3, resulting in enhanced glucose-sensing performance, which, in turn, qualitatively supports our experimental data. Hence, our experimental data and theoretical insight from the electronic structure simulations conclude that Pd-doped monoclinic WO3 is a potential material for the fabrication of real-time glucose sensors.

Tuning the pure monoclinic phase of WO3 and WO3-Ag nanostructures for non-enzymatic glucose sensing application with theoretical insight from electronic structure simulations

Here, we report the controlled hydrothermal synthesis and tuning of the pure monoclinic phase of WO3 and WO3-Ag nanostructures. Comparative electrochemical nonenzymatic glucose sensing properties of WO3 and WO3-Ag were investigated by cyclic voltammetry and chronoamperometric tests. We observed enhanced glucose sensing performance of WO3-Ag porous spheres as compared to bare WO3 nanoslabs. The sensitivity of the pure WO3 nanoslabs is 11.1 μA μM−1 cm−2 whereas WO3-Ag porous spheres exhibit sensitivity of 23.3 μA μM−1 cm−2. The WO3-Ag porous spheres exhibited a good linear range (5–375 μM) with excellent anti-interference property. Our experimental observations are qualitatively supported by density functional theory simulations through investigation of bonding and charge transfer mechanism of glucose on WO3 and Ag doped WO3. As the binding energy of glucose is more on the Ag doped WO3 (100) surface compared to the bare WO3 (100) surface and the Ag doped WO3 (100) surface becomes more conducting due to enhancement of density of states near the Fermi level, we can infer that Ag doped WO3 exhibits a better charge transfer media compared to bare WO3 resulting in enhanced glucose sensitivity in consistency with our experimental data.

A visible-light-driven heterojuncted composite WO3/Bi12O17Cl2: Synthesis, characterization, and improved photocatalytic performance

Novel visible-light-driven WO3/Bi12O17Cl2 heterojuncted photocatalysts with different mass ratios were successfully fabricated by a facile hydrothermal process and were characterized by XRD, UV–Vis DRS, SEM, TEM, HRTEM, XPS, BET, Raman, PL, and ESR techniques. The original morphology of Bi12O17Cl2 was maintained after the addition of WO3 nanoparticles and the specific surface area values of WBx composites were obviously enlarged. The intimate contact of both components in HRTEM confirmed the generation of smooth phase interface. These as-prepared samples were subjected to the photocatalytic degradation of dye rhodamine B (RhB) and tetracycline hydrochloride (TC) under visible light irradiation (λ≥420nm). Under identical conditions, WBx composites showed greatly enhanced photocatalytic performance in comparison to bare WO3 and Bi12O17Cl2. Especially, the sample WB0.5 exhibited the highest photocatalytic removal outcome over RhB among all tested candidates and owned an apparent rate constant about 73.7, 7.1, 15.8 times of those pure WO3, Bi12O17Cl2, and N-doped TiO2, respectively. The enhancement of photocatalytic capability of composites mainly attributed to the suitable morphology, enlarged specific surface areas, strengthened optical property, and favorable well-aligned straddling band-structures. Active species entrapping experiments confirmed holes and superoxide radicals as major oxidative species, by which, a possible photocatalytic mechanism was primarily proposed.

Enhanced Interfacial Charge Transfer on a Tungsten Trioxide Photoanode with Immobilized Molecular Iridium Catalyst.

The rational design of active photoanodes for photoelectrochemical (PEC) water splitting is crucial for future applications in sustainable energy conversion. A combination of catalysts with photoelectrodes is generally required to improve surface kinetics and suppress surface recombination. In this study, we present WO3 photoanode modified with the iridium complex [(H4 dphbpy)IrIII (Cp*)Cl]Cl (Ir-PO3 H2 ; H4 dphbpy=2,2'-bipyridine-4,4'-bisphosphonic acid, Cp*=pentamethylcyclopentadiene (WO3 +Ir-PO3 H2 )- for PEC water oxidation. When Ir-PO3 H2 is anchored to a WO3 electrode, the photoanode shows a significant improvement in both photocurrent and faradaic efficiency compared to the bare WO3 photoanode. Under simulated sunlight illumination (AM 1.5G, 100 mW cm-2 ) with an applied bias of 1.23 V (vs. reversible hydrogen electrode), the photoanode exhibits a photocurrent of 1.16 mA cm-2 in acidic conditions, which is double that of the bare WO3 photoanode. The faradaic efficiency is promoted from 56 % to 95 %. Kinetic studies reveal that Ir-PO3 H2 exhibits a different interfacial charge-transfer mechanism on the WO3 photoanode for PEC water oxidation compared to iridium oxide. Ir-PO3 H2 , as a water-oxidation catalyst, can accelerate the surface charge transfer through rapid surface kinetics.

Robust Co-catalytic Performance of Nanodiamonds Loaded on WO3 for the Decomposition of Volatile Organic Compounds under Visible Light

Proper co-catalysts (usually noble metals), combined with semiconductor materials, are commonly needed to maximize the efficiency of photocatalysis. Search for cost-effective and practical alternatives for noble-metal co-catalysts is under intense investigation. In this work, nanodiamond (ND), which is a carbon nanomaterial with a unique sp3(core)/sp2(shell) structure, was combined with WO3 (as an alternative co-catalyst for Pt) and applied for the degradation of volatile organic compounds under visible light. NDs-loaded WO3 showed a highly enhanced photocatalytic activity for the degradation of acetaldehyde (∼17 times higher than bare WO3), which is more efficient than other well-known co-catalysts (Ag, Pd, Au, and CuO) loaded onto WO3 and comparable to Pt-loaded WO3. Various surface modifications of ND and photoelectochemical measurements revealed that the graphitic carbon shell (sp2) on the diamond core (sp3) plays a crucial role in charge separation and the subsequent interfacial charge transfer. As a...

Multilayer Active Nanostructures of Metal Oxide Semiconductors-Assisted Photooxidation of Wastewater for Voltammetric Determination of Heavy Metals

The presence of organic matter (e.g. surfactants) is the most crucial problem in many analytical methods, such as inductively coupled plasma mass spectrometry (ICP MS), graphite furnace atomic absorption spectrometry (GF AAS) or electrochemical methods (stripping voltammetry). Voltammetry is a sensitive method of metal determination, only one an alternative to ICP MS. Only one limitation of the method is an influence of the organic matrix on the measurements. After the wet digestion with H2O2 accelerated with UV irradiation the evaporation of an excess of reagent is required. We present the application of “sunlight” assisted digestion in the presence of bare WO3 or multilayer metal oxide semiconductors (e.g. WO3 and Fe2O3) to the decomposition of dissolved organic matter, using the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant (1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton™X-114) in natural water samples, prior to the determination of traces residues of lead by stripping voltammetry methods. The results of the study showed firstly that the preparation of reproducible WO3 layers characterized by high mechanical and chemical resistance was possible, and secondly that it was also possible to obtain a high efficiency of decomposition, equal in efficiency to that of the reference method, which was the hydrogen peroxide oxidation assisted by UV, with evaporation nearly to dryness. The developed procedure is suggested to be a no-reagents method for the decomposition of added SDS, leading to 100 % recovery of added Pb (II). Physicochemical properties (structure, morphology and spectroscopic identity) of the resulting hybrid (composite) WO3 films were assessed using X-ray diffraction, scanning electron microscopy, as well as UV-Vis and Raman spectroscopies. The electrochemical method (anodic stripping voltammetric - ASV) will be applied in practical study of the determination of various trace metals in natural water samples. For comparison, GFAAS and ICP-MS measurements would be performed as reference methods confirming the correctness of electrochemical measurements due to their different tolerance to the presence of the organic matrix in the samples.

P-Type PdO nanoparticles supported on n-type WO3 nanoneedles for hydrogen sensing

We report the synthesis of palladium nanoparticle (NP) decorated WO3 nanoneedles (NNs) employing a single-step, aerosol assisted chemical vapor deposition approach. Two different Pd precursors were investigated in view of optimizing the morphology and the gas sensing performance of the resulting nanostructured films. In particular, palladium acetylacetonate was found to be more suitable than ammonium hexachloropalladate for obtaining n-type WO3 NNs uniformly decorated with well dispersed p-type PdO NPs. The active films could be directly deposited on the electrode area of microelectromechanical system-based resistive transducers. The morphology and chemical composition of the films was investigated by scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy analysis. PdO-decorated WO3 NNs show a response toward hydrogen that is about 680 times higher than that of bare WO3 NNs. Finally, PdO-loaded sensors display extremely low-cross sensitivity to water vapor, which makes them remarkably immune to changes in the background humidity.

Conformally coated BiVO4 nanodots on porosity-controlled WO3 nanorods as highly efficient type II heterojunction photoanodes for water oxidation

Bismuth vanadate (BiVO4) has become a hot topic for solar hydrogen generation by water oxidation due to its appropriate band edges, and narrow band gap. However, the actual conversion efficiency achieved with BiVO4-based photoanodes is considerably less than the theoretical values because of drawbacks such as poor electron transportation and slow kinetics of oxygen evolution. In these respects, formation of nanostructured heterojunctions is considered to have a marked effect in terms of improving the photoactivities of BiVO4 photoanodes since it is possible to enhance the charge transfer at the interface and increase light absorption significantly. Herein, we report the synthesis and photoelectrochemical (PEC) properties of various BiVO4-based heterojunction anodes based on stoichiometric BiVO4 by pulsed electrodeposition. We show that WO3 is the optimum bottom layer for a type II band system with BiVO4 among various metal oxides. It is revealed that the photocurrent density of bare WO3 nanorods can be changed drastically by controlling the porosity and aspect ratio and thus BiVO4/WO3 heterojunction anodes show as similar tendency to bare WO3 nanorods. Under the optimum conditions, a BiVO4/WO3 heterojunction anode can lead to a high photocurrent density of 4.55mA/cm2 and an incident photon to current conversion efficiency of 80% at 1.23V versus a reversible hydrogen electrode without additional catalyst. Cross-sectional transmission electron microscopy shows that dot-like BiVO4 is well decorated on the entire surface of WO3 nanorods. This systematic study provides a viewpoint on the crucial role of the active area of the bottom layer for high-performance BiVO4-based type II heterojunction photoanodes, and the proposed concept is applicable to various photoelectrode systems.

Mesoporous WN/WO3-Composite Nanosheets for the Chemiresistive Detection of NO2 at Room Temperature

Composite materials, which can optimally use the advantages of different materials, have been studied extensively. Herein, hybrid tungsten nitride and oxide (WN/WO3) composites were prepared through a simple aqueous solution route followed by nitriding in NH3, for application as novel sensing materials. We found that the introduction of WN can improve the electrical properties of the composites, thus improving the gas sensing properties of the composites when compared with bare WO3. The highest sensing response was up to 21.3 for 100 ppb NO2 with a fast response time of ~50 s at room temperature, and the low detection limit was 1.28 ppb, which is far below the level that is immediately dangerous to life or health (IDLH) values (NO2: 20 ppm) defined by the U.S. National Institute for Occupational Safety and Health (NIOSH). In addition, the composites successfully lower the optimum temperature of WO3 from 300 °C to room temperature, and the composites-based sensor presents good long-term stability for NO2 of 100 ppb. Furthermore, a possible sensing mechanism is proposed.