Fabrication of (001)-oriented monoclinic WO3 films on FTO substrates

Recent Developments in Nickel-Based Layered Double Hydroxides for Photo(-/)electrocatalytic Water Oxidation

Layered double hydroxides (LDHs), especially those containing nickel (Ni), are increasingly recognized for their potential in photo(-/)electrocatalytic water oxidation due to the abundant availability of Ni, their corrosion resistance, and their minimal toxicity. This review provides a comprehensive examination of Ni-based LDHs in electrocatalytic (EC), photocatalytic (PC), and photoelectrocatalytic (PEC) water oxidation processes. The review delves into the operational principles, highlighting similarities and distinctions as well as the benefits and limitations associated with each method of water oxidation. It includes a detailed discussion on the synthesis of monolayer, ultrathin, and bulk Ni-based LDHs, focusing on the merits and drawbacks inherent to each synthesis approach. Regarding the EC oxygen evolution reaction (OER), strategies to improve catalytic performance and insights into the structural evolution of Ni-based LDHs during the electrocatalytic process are summarized. Furthermore, the review extensively covers the advancements in Ni-based LDHs for PEC OER, including an analysis of semiconductors paired with Ni-based LDHs to form photoanodes, with a focus on their enhanced activity, stability, and underlying mechanisms facilitated by LDHs. The review concludes by addressing the challenges and prospects in the development of innovative Ni-based LDH catalysts for practical applications. The comprehensive insights provided in this paper will not only stimulate further research but also engage the scientific community, thus driving the field of photo(-/)electrocatalytic water oxidation forward.

Rapid Fabrication of Tungsten Oxide-Based Electrochromic Devices through Femtosecond Laser Processing

The sol-gel method is a widely adopted technique for the preparation of tungsten trioxide (WO3) materials, favored for its cost-effectiveness and straightforward production procedures. However, this method encounters challenges such as prolonged annealing periods and limited flexibility in fabricating patterned WO3 films. This study introduces a novel approach that integrates femtosecond laser processing with the sol-gel method to enhance the fabrication of WO3 films. By adjusting polyvinylpyrrolidone (PVP) concentrations during sol-gel synthesis, precise control over film thickness and optimized film properties were achieved. The innovative technique significantly reduced the annealing time required to achieve an 80% transmittance rate from 90 min to 40 min, marking a 56% decrease. Laser processing increased the surface roughness of the films from Sa = 0.032 to Sa = 0.119, facilitating enhanced volatilization of organics during heat treatment. Additionally, this method improved the transmittance modulation of the films by 22% at 550 nm compared to unprocessed counterparts. This approach not only simplifies the manufacturing process but also enhances the optical efficiency of electrochromic devices, potentially leading to broader applications and more effective energy conservation strategies.

Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis

Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.

Review on recent progress in WO3-based electrochromic films: preparation methods and performance enhancement strategies

Transition metal oxides have drawn tremendous interest due to their unique physical and chemical properties. As one of the most promising electrochromic (EC) materials, tungsten trioxide (WO₃) has attracted great attention due to its exceptional EC characteristics. This review summarizes the background and general concept of EC devices, and key criteria for evaluation of WO₃-based EC materials. Special focus is placed on preparation techniques and performance enhancement of WO₃ EC films. Specifically, four methods - nanostructuring, regulating crystallinity, fabricating hybrid films, and preparing multilayer composite structures - have been developed to enhance the EC performance of WO₃ films. Finally, we offer some important recommendations and perspectives on potential research directions for further study.

Crystal Facet-Modulated WO3 Nanoplate Photoanode for Photoelectrochemical Glyoxal Semi-oxidation into Glyoxylic Acid

Transforming glyoxal to value-added glyoxylic acid (GA) is highly desirable but challenging due to the uncontrollable over-oxidation. In this work, we report on a first demonstration of semi-oxidation of glyoxal with high selectivity (86.5%) and activity on WO₃ nanoplate photoanode through the photoelectrochemical strategy. The optimization of reactivity was achieved via crystal facet regulation, showing a satisfactory GA production rate of 308.4 mmol m^-2 h^-2, 84.0% faradaic efficiency, and 4.3% total solar-to-glyoxylic acid efficiency on WO₃ with enriched {200} facets at 1.6 V versus RHE. WO₃ with a high {200} facet ratio exhibits more efficient electron-hole transfer kinetics, resulting in the facilitated formation of hydroxyl radicals (^•OH) and glyoxal radicals. Meanwhile, the theoretical calculation results indicate that the high selectivity and activity come from the strong adsorption ability for glyoxal and the low reaction energy for glyoxal radical generation on the (200) facets of WO₃. Moreover, the high energy demand toward oxalic acid production on WO₃ leads to the exciting semi-oxidation process.

Activating a TiO2/BiVO4 Film for Photoelectrochemical Water Splitting by Constructing a Heterojunction Interface with a Uniform Crystal Plane Orientation

The construction of a heterojunction has been considered one of the most effective strategies to improve the photoelectrochemical (PEC) performance of photoanodes; however, most researchers only focus on the design and preparation of a novel and efficient heterojunction photoelectrode, and the investigation on the effect of the heterojunction interface structure on PEC performance is ignored. In this work, a TiO₂/BiVO₄ photoanode with a uniform crystal plane orientation in the heterojunction interface (TiO₂-110/BiVO₄-202) was prepared by an in situ transformation method. We found that the PEC activity of the TiO₂/BiVO₄ photoanode can be activated by constructing such a heterojunction interface. Compared with a TiO₂/BiVO₄ photoanode with a random crystal plane orientation prepared by a simple soaking-calcining method (S-TiO₂/BiVO₄, 0.04 mA/cm² at 1.23 V_RHE), the TiO₂/BiVO₄ photoanode prepared by the in situ transformation method (I-TiO₂/BiVO₄) exhibits a significantly better PEC performance, and the photocurrent density of I-TiO₂/BiVO₄ is about 2.2 mA/cm² at 1.23 V_RHE under visible light irradiation without a cocatalyst. This is mainly attributed to the fact that I-TiO₂/BiVO₄ has a faster electron transfer rate in the heterojunction interface according to the results of PEC analysis. Furthermore, density functional theory (DFT) calculations show that the BiVO₄-202 surface has a higher Fermi energy level, thereby expediting the photogenerated carrier transport in the heterojunction interface. This work corroborates and strengthens the view that the heterojunction interface structure has a significant effect on the PEC performance.

Two-dimensional WO3 nanosheets for high-performance electrochromic supercapacitors

The 2D single crystal WO3 nanosheets with (101) preferred orientation facets self-assembled on an FTO substrate and were applied to an aqueous electrochromic-supercapacitor.

Oxygen Vacancy-Enhanced Photoelectrochemical Water Splitting of WO3/NiFe-Layered Double Hydroxide Photoanodes

Photoelectrochemical (PEC) water splitting serves as one of the promising approaches for producing clean and renewable energy, and their solar-hydrogen energy conversion efficiency depends on the interfacial charge separation and carrier mobility. Herein, we report an effective strategy to promote the PEC performance by fabricating a WO₃ photoanode rich in oxygen vacancies (Ov) modified by NiFe-based layered double hydroxide (LDH). When WO₃-Ov/NiFe-LDH is used as a photoanode, the maximum photocurrent density at 1.8 V versus RHE has been significantly enhanced to 2.58 mA·cm^-2, which is 4.3 times higher than that of WO₃. In addition, analogues were studied in controlled experiments without Ov, which further demonstrated that the synergistic effect of NiFe-LDH and Ov resulted in increased carrier concentration and driving force. According to electrical impedance spectroscopy, X-ray photoelectron spectroscopy, and Mott-Schottky analysis, the built-in electronic field in WO₃ homojunction, along with the accelerated hole capture by the NiFe-LDH cocatalyst contributes to the improved charge separation and transport in the WO₃-Ov/NiFe-LDH electrode. This work proposes an efficient and valuable strategy for designing the structure of WO₃-based photoelectrodes.

Z-Scheme Photocarrier Transfer Realized in Tungsten Oxide-Based Photocatalysts by Combining with Bismuth Vanadate Quantum Dots

Multicomponent photocatalysts with a Z-scheme charge transfer are promising in converting solar to hydrogen fuel because of their significantly improved light absorption and restrained photocarrier recombination while keeping their redox capacity. In this work, a composite photocatalyst of BiVO₄ quantum dot-decorated WO₃ nanosheet arrays was synthesized and investigated. The existence of the Z-scheme charge transfer behavior was confirmed by the redox probe technique. Such a Z-scheme charge transfer makes it possible to generate hydrogen without bias. An optimized photocatalyst produces a hydrogen generation rate of 0.75 μmol/h without bias and a photocurrent of 1.91 mA/cm² at 1.23 V versus RHE, which is about 70% higher than that of pure WO₃. We attributed these improvements to the enhanced light absorption, extended conduction band level of BiVO₄, as well as the unique charge transfer behavior in the Z-scheme structure. This work presents a generalizable method to improve the redox capacity of a variety of semiconductors through rationally selecting the building material blocks in view of energy levels.

Robust charge carrier by Fe3O4 in Fe3O4/WO3 core-shell photocatalyst loaded on UiO-66(Ti) for urea photo-oxidation

In this study, a facile four-step hydrothermal method was utilized to deposit a core-shell structure on UiO-66(Zr/Ti) nanoflake (NFs) as a visible-light-driven photocatalyst. The core was magnetic Fe₃O₄ which served as a charge carrier coated with WO₃ shell. The as-prepared photocatalyst was characterized by XRD, VSM, BET, FTIR, FE-SEM, UV-Vis-DRS, and PL techniques which proved successful deposition of Fe₃O₄@WO₃ core/shell particle on UiO-66(Zr/Ti)-NFs. The obtained photocatalyst was subsequently applied for urea photo-oxidation. This magnetically recoverable photocatalyst exhibited superior activity due to its desirable band alignment, high stability, and generation of the photo-induced charge carriers, as well as providing a high surface area with low mass transfer resistance. Fe₃O₄ core acted as charge-carrier to transport the photogenerated charges of UiO-66(Zr/Ti)-NFs (electron-donor) to WO₃ charge-collectors for effective photoconversion. The central composite design was applied to design the experiments matrix in which flow rate, pH, irradiation time, catalyst mass, and initial urea concentration were considered as operational factors. The optimized condition was found by defining the desirability function. 90% degradation percentage was achieved at 550 mL/min solution flowrate, pH = 7, 120 min irradiation time, 0.22 g UiO-66(Zr)-NFs-Fe₃O₄@WO_3, and 40 mg/L of the initial concentration of urea with the desirability value of 0.89. Such a superior photocatalytic activity of UiO-66-Fe₃O₄@WO₃ can be ascribed to the reclamation of Fe₃O₄ as a low bandgap carrier, which accelerated the conveyance of electrons and followed surpassing charge separation. Our present findings open a new strategy to produce a wide range of core-shell heterogeneous catalysts to be applied in photoreactors scale-up.

UiO-66(Ti)-Fe3O4-WO3 photocatalyst for efficient ammonia degradation from wastewater into continuous flow-loop thin film slurry flat-plate photoreactor

This work presents the characterization of novel synthesized UiO-66(Ti)-Fe₃O₄-WO₃ magnetic photocatalyst and investigates their photocatalytic activity for the photodegradation of ammonia in a designed continuous flow-loop thin-film slurry flat-plate photoreactor (TFSR). Excellent ammonia degradation efficiency was achieved in the presence of the synthesized catalyst at ambient conditions using no more reactive oxidant species. Several independent variables involving catalyst mass, flowrate, pH, irradiation time and initial ammonia concentration as well as corresponding experiments were analyzed and design using the central composite design (CCD). The influence and significance of each parameter and their binary interactions were then evaluated by applying the analysis of variance. The ammonia degradation efficiency of 91.80 % with the desirability of 0.903 were obtained at optimum values of operational parameters including 550 mL/min,10, 0.125 g/L, 60 min and 30 mg/L for solution flowrate, pH, catalyst mass, irradiation time and initial ammonia concentration, respectively. Furthermore, the liquid phase products of ammonia degradation such as nitrate and nitrite ions were completely removed, and purified water was produced using the combination of reverse osmosis process and mixed resins beds. The photocatalyst mechanism study revealed that [Formula: see text] was the predominant reactive oxygen species in the ammonia photodegradation.

Enhanced photoelectrocatalytic degradation of bisphenol A and simultaneous production of hydrogen peroxide in saline wastewater treatment

The degradation of organic pollutants in saline wastewater has been a challenge for environmental remediation. In this study, a two-chamber cell was structured to simultaneously degrade organic contaminants (bisphenol A, BPA) from saline wastewater and produce hydrogen peroxide (H₂O₂). In the anode chamber, a new solar-light-driven system was devised using chloride ions (Cl‾) as a medium and WO₃ photoanode as a radical initiator. Under solar light irradiation, photogenerated holes yielded at the WO₃ photoanode promoted the conversion of Cl‾ to reactive chlorine species, which could oxidize BPA more rapidly. The results indicated that the BPA removal can be significantly enhanced by increasing pH to 10.8 or increasing the Cl‾ concentration to 200 mM. At these conditions, 92% BPA was degraded into CO₂ and H₂O in 120 min. In the cathode chamber, a new dopamine modified carbon felt (CF-DPA) cathode was employed to produce H₂O₂, obtaining a high concentration of 5.4 mM under optimum conditions. The electrochemical analyses for CF-DPA revealed that dopamine modification promoted electron transfer and enhanced the two-electron oxygen reduction to increase H₂O₂ yields.

Crystal Facet Engineering of Photoelectrodes for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article. After the Introduction, the second section of this review concisely introduces the mechanisms of crystal facet engineering. The subsequent section provides a snapshot of the unique facet-dependent properties of some semiconductor crystals including surface electronic structures, redox reaction sites, surface built-in electric fields, molecular adsorption, photoreaction activity, photocorrosion resistance, and electrical conductivity. Then, the methods for fabricating photoelectrodes with faceted semiconductor crystals are reviewed, with a focus on the preparation processes. In addition, the notable advantages of the crystal facet engineering of photoelectrodes in terms of light harvesting, charge separation and transfer, and surface reactions are critically discussed. This is followed by a systematic overview of the modification strategies of faceted photoelectrodes to further enhance the PEC performance. The last section summarizes the major challenges and some invigorating perspectives for future research on crystal facet engineered photoelectrodes, which are believed to play a vital role in promoting the development of this important research field.

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.

Nanostructure-induced performance degradation of WO3·nH2O for energy conversion and storage devices

Although 2D layered nanomaterials have been intensively investigated towards their application in energy conversion and storage devices, their disadvantages have rarely been explored so far especially compared to their 3D counterparts. Herein, WO₃·nH₂O (n = 0, 1, 2), as the most common and important electrochemical and electrochromic active nanomaterial, is synthesized in 3D and 2D structures through a facile hydrothermal method, and the disadvantages of the corresponding 2D structures are examined. The weakness of 2D WO₃·nH₂O originates from its layered structure. X-ray diffraction and scanning electron microscopy analyses of as-grown WO₃·nH₂O samples suggest a structural transition from 2D to 3D upon temperature increase. 2D WO₃·nH₂O easily generates structural instabilities by 2D intercalation, resulting in a faster performance degradation, due to its weak interlayer van der Waals forces, even though it outranks the 3D network structure in terms of improved electronic properties. The structural transformation of 2D layered WO₃·nH₂O into 3D nanostructures is observed via ex situ Raman measurements under electrochemical cycling experiments. The proposed degradation mechanism is confirmed by the morphology changes. The work provides strong evidence for and in-depth understanding of the weakness of 2D layered nanomaterials and paves the way for further interlayer reinforcement, especially for 2D layered transition metal oxides.

Photoelectrochemical Response of WO3/Nanoporous Carbon Anodes for Photocatalytic Water Oxidation

This work demonstrates the ability of nanoporous carbons to boost the photoelectrochemical activity of hexagonal and monoclinic WO3 towards water oxidation under irradiation. The impact of the carbonaceous phase was strongly dependent on the crystalline structure and morphology of the semiconductor, substantially increasing the activity of WO3 rods with hexagonal phase. The incorporation of increasing amounts of a nanoporous carbon of low functionalization to the WO3 electrodes improved the quantum yield of the reaction and also affected the dynamics of the charge transport, creating a percolation path for the majority carriers. The nanoporous carbon promotes the delocalization of the charge carriers through the graphitic layers. We discuss the incorporation of nanoporous carbons as an interesting strategy for improving the photoelectrochemical performance of nanostructured semiconductor photoelectrodes featuring hindered carrier transport.

Highly selective transformation of ammonia nitrogen to N2 based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions system

A highly selective method for transforming ammonia nitrogen to N₂ was proposed, based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions (PEC-chlorine) system. The PEC-chlorine system was facilitated by a visible light response WO₃ nanoplate array (NPA) electrode in an ammonia solution containing chloride ions (Cl^-). Under illumination, photoholes from WO₃ promote the oxidation of Cl^- to chlorine radical (Cl). This radical can selectively transform ammonia nitrogen to N₂ (79.9%) and NO₃^- (19.2%), similar to the breakpoint chlorination reaction. The ammonia nitrogen removal efficiency increased from 10.6% (PEC without Cl^-) to 99.9% with the PEC-chlorine system within 90 min operation, which can be attributed to the cyclic reactions between Cl^-/Cl and the reaction intermediates (NH₂, NHCl, etc.) that expand the degradation reactions from the surface of the electrodes to the whole solution system. Moreover, Cl is the main radical species contributing to the transformation of ammonia nitrogen to N₂, which is confirmed by the tBuOH capture experiment. Compared to conventional breakpoint chlorination, the PEC-chlorine system is a more economical and efficient means for ammonia nitrogen degradation because of the fast removal rate, no additional chlorine cost, and its use of clean energy (since it is solar-driven).

Recent Progress in Energy-Driven Water Splitting

Hydrogen is readily obtained from renewable and non-renewable resources via water splitting by using thermal, electrical, photonic and biochemical energy. The major hydrogen production is generated from thermal energy through steam reforming/gasification of fossil fuel. As the commonly used non-renewable resources will be depleted in the long run, there is great demand to utilize renewable energy resources for hydrogen production. Most of the renewable resources may be used to produce electricity for driving water splitting while challenges remain to improve cost-effectiveness. As the most abundant energy resource, the direct conversion of solar energy to hydrogen is considered the most sustainable energy production method without causing pollutions to the environment. In overall, this review briefly summarizes thermolytic, electrolytic, photolytic and biolytic water splitting. It highlights photonic and electrical driven water splitting together with photovoltaic-integrated solar-driven water electrolysis.

Iron cation-induced biphase symbiosis of h-WO3/o-WO3·0.33H2O and their crystal phase transition

h-WO₃ and o-WO₃·0.33H₂O were proved to coexist in the same hexagonal prism nanoparticle via combination of instrumental characterization and the software simulation.

Effect of the morphology and phases of WO3 nanocrystals on their photocatalytic efficiency

Understanding of the effect of the morphology and crystal phase on photocatalytic efficiency and their precise control are still a great challenge in photocatalysis.

Augmented Z scheme blueprint for efficient solar water splitting system using quaternary chalcogenide absorber material

Band energetics of protected CZTS cell and other photoanodes in electrolyte.

Etching treatment of vertical WO3 nanoplates as a photoanode for enhanced photoelectrochemical performance

An innovative etching method was developed to increase surface voids, active crystal facets and surface groups, which led to improved photocurrent performance.

Tungsten Oxides for Photocatalysis, Electrochemistry, and Phototherapy

The conversion, storage, and utilization of renewable energy have all become more important than ever before as a response to ever-growing energy and environment concerns. The performance of energy-related technologies strongly relies on the structure and property of the material used. The earth-abundant family of tungsten oxides (WOx ≤3 ) receives considerable attention in photocatalysis, electrochemistry, and phototherapy due to their highly tunable structures and unique physicochemical properties. Great breakthroughs have been made in enhancing the optical absorption, charge separation, redox capability, and electrical conductivity of WOx ≤3 through control of the composition, crystal structure, morphology, and construction of composite structures with other materials, which significantly promotes the efficiency of processes and devices based on this material. Herein, the properties and synthesis of WOx ≤3 family are reviewed, and then their energy-related applications are highlighted, including solar-light-driven water splitting, CO2 reduction, and pollutant removal, electrochromism, supercapacitors, lithium batteries, solar and fuel cells, non-volatile memory devices, gas sensors, and cancer therapy, from the aspect of function-oriented structure design and control.

Tungsten trioxide nanoplate array supported platinum as a highly efficient counter electrode for dye-sensitized solar cells

A tungsten trioxide (WO₃) nanoplate array is fabricated directly on the FTO/glass substrate and used as a platinum (Pt) nanoscale supporter for a highly efficient and low Pt-consumption counter electrode (CE) in dye-sensitized solar cells (DSCs). A Pt/WO₃ composite structure, with Pt nanoparticles having a diameter of 2-3 nm, increases the electrochemical catalytic activity in catalyzing the reduction of triiodide. Accordingly, the power conversion efficiency is increased from less than 1% for WO₃ CE and 8.1% for Pt CE, respectively, to 8.9% for Pt/WO₃ CE. Moreover, the use of Pt/WO₃ CE can dramatically reduce the consumption of scarce Pt material, with a relatively low Pt-loading of ∼2 μg cm(-2), while maintaining a much better performance. The excellent performance of Pt/WO₃ CE is attributed to the efficient electron injection and transport via WO₃ supporters, as well as the nanostructure array morphology of WO₃ for deposition of fine Pt nanoparticles. This work provides an approach for developing highly catalytic and low-cost Pt based CEs, which also has implications for the development of Pt/WO₃ nanoplate arrays for other applications.

Iron-doping-enhanced photoelectrochemical water splitting performance of nanostructured WO3: a combined experimental and theoretical study

In this paper, we have studied Fe-doping of nanostructured tungsten trioxide (WO3) and its pronounced effect in promoting the photoelectrochemical (PEC) water splitting performance. Vertically aligned Fe-doped WO3 nanoflakes on fluorine-doped tin oxide (FTO) were synthesized via the hydrothermal method. An X-ray photoelectron spectroscopy (XPS) analysis confirmed the Fe(3+) substitution at the W(6+) site in the prepared films. Broadened visible light absorption was observed in doped films, likely due to the formation of extra band states through doping. The Fe-doping was shown to greatly improve the PEC water splitting performance of WO3. More specifically, the 2 mol% Fe-doped WO3 achieved a photocurrent density of 0.88 mA cm(-2) at 1.23 V versus RHE, approximately 30% higher than that of the undoped WO3 (0.69 mA cm(-2) at 1.23 V versus RHE). This enhancement was attributed to the reduced band gap and the doping-enhanced charge carrier density as confirmed by the absorption spectra and the Mott-Schottky plots, respectively. Finally, first-principles density functional theory (DFT) calculations confirmed that the formation of oxygen vacancies was favored after Fe-doping, contributing to the increased charge carrier density in slightly doped films.

Tuning of the crystal engineering and photoelectrochemical properties of crystalline tungsten oxide for optoelectronic device applications

WO₃crystals with {002} or {111} facets primarily exposed, WO₃films with dominant orientations, doping and heterostructuring are highlighted.

Construction of hydrated tungsten trioxide nanosheet films for efficient electrochromic performance

Two-dimensional WO₃ (hydrate) nanosheets, with high surface ratio and permeable channels, could be a promising building block for constructing EC electrode.

ZnO nanoparticle-functionalized WO3 plates with enhanced photoelectrochemical properties

ZnO nanoparticle-functionalized WO₃ plates were prepared via an electrodeposition and an electrochromism reaction of WO₃, and the composites improve the separation of photogenerated electrons and holes.

Facile preparation of hierarchical TiO2 nano structures: growth mechanism and enhanced photocatalytic H2 production from water splitting using methanol as a sacrificial reagent

Owing to unique features, hierarchical nanostructure of TiO2 has superior photocatalytic activity. In this work a facile hydrothermal route has been explored to prepare 3D hierarchical TiO2 (3D-HTiO2), 1D/3D hybrid hierarchical TiO2 composite (HHC), and 3D hierarchical protonated titanate microspheres H2Ti2O5·H2O (3DHPTMS) at the expense of free-standing titania nanotube membrane (TiO2-Memb). It proceeded through the formation of peroxotitanium complex, a water-soluble Ti complex as an intermediate. Mechanism of formation, role of membrane crystallinity, and reaction parameters giving fine control on tuning morphology and crystal structure have been investigated systematically. Photocatalytic activities were determined by measuring the amount hydrogen generated from water splitting under UV irradiation in the presence of methanol as a sacrificial reagent. Self-assembled hierarchical titania nanostructures exhibited much superior photocatalytic activity compared to that of starting material, i.e., TiO2-Memb. Enhanced photocatalytic activity is due to characteristic morphology, increased surface area, and enhanced production of photogenerated charge carriers.

Synthesis of three-dimensional WO3 octahedra: characterization, optical and efficient photocatalytic properties

First time synthesized novel WO₃ octahedra exhibited photocatalytic performance of about 5.33 times than that of bulk which may be attributed to large surface area and highly reactive facet {120}.