Tungsten Modification Research Articles

Pre-introducing Li4NiWO6 defect phase by tungsten modification enables highly stabilized Ni-rich cathode

Tungsten (W) has attracted considerable attention as a promising dopant capable of enhancing the structural stability of Ni-rich cathode materials. However, investigations into W modification remain highly debated due to the elusive mechanisms involved, particularly in determining whether W is doped into the lattice structure or exists as a distinct phase on the surface of the particles. In this work, we systematically observe the effects induced by the introduction of W into LiNi0.9Co0.05Mn0.05O2 (NCM). We discovered that during high-temperature solid-state reactions, W-containing substances tend to react preferentially with surface Li, creating a lithium-deficient state on the NCM surface, resulting in the generation of Li4NiWO6. Molecular dynamics simulations tracking Li, W, and Ni elemental changes at the interface confirm the initial creation of Li6WO6, succeeded by diffusion of Ni to replace Li, forming Li4NiWO6. The pre-introducing Li4NiWO6 defect phase can effectively absorb anisotropic lattice strain, preserving the mechanical integrity of the secondary particles. Furthermore, the Li4NiWO6 phase, combined with the amorphous LixWyOz coating layer, effectively acts as a guard against undesirable interfacial side reactions, ultimately imparting excellent electrochemical performance to NCM. Understanding the dynamic processes of interfacial reactions is crucial for tailoring surface properties of Ni-rich cathodes towards long-life lithium-ion batteries.

High‐performance bismuth titanate‐ferrite (Bi5Ti3FeO15) for high‐temperature piezoelectric applications

AbstractAdvancing the development of high‐temperature piezoelectric sensors requires high‐performance piezoelectric materials with high Curie temperatures, wherein the charge signals can be efficiently collected at elevated temperatures. The bismuth layer‐structured ferroelectric (BLSF) bismuth titanate‐ferrite (Bi5Ti3FeO15, BTF) has recently attracted considerable attention because of its high Curie temperature (TC) of ∼761°C. However, the piezoelectric properties of BTF‐based compounds have not been extensively investigated because of their extremely poor piezoelectric performances and low electrical resistivities at elevated temperatures. Herein, tungsten‐substituted BTF (BTF‐100xW) ceramics were synthesized using a solid‐state reaction method. X‐ray diffraction refinement results confirmed the lattice distortion of the BO6 octahedron, while piezoelectric force microscopy images verified an increase in the domain wall density with tungsten modification, both of which contribute to significant enhancement of the piezoelectric properties of BTF‐100xW as intrinsic and extrinsic contributions, respectively. Remarkably, BTF‐3W exhibits a high TC of 793°C and a large piezoelectric constant (d33) of 24.3 pC/N, which is over three times that of BTF (7.1 pC/N). Importantly, the substitution of tungsten decreases the concentration of oxygen vacancies, increases the direct current electrical resistivity, and improves the electrical homogeneity at high temperatures, resulting in extremely stable piezoelectric and electromechanical properties at high temperatures, with a high in‐situ relative d33 of >90% at 400°C and a small variation in the electromechanical coupling factor (kp) of <8% at temperatures up to 450°C. These results suggest that the tungsten‐substituted BTF is a potential candidate for high‐temperature piezoelectric ceramics, and is a promising material for applications in high‐temperature piezoelectric sensors.

Insight into the remarkable enhancement of NH3-SCR performance of Ce-Sn oxide catalyst by tungsten modification

A series of W-modified Ce-Sn catalysts were fabricated and investigated for the selective catalytic reduction (SCR) of NOx (NO and NO2) by NH3. All the prepared Ce-W-Sn ternary oxide catalysts showed higher deNOx efficiency than the Ce-Sn catalysts, among which the Ce1W0.24Sn2Ox catalyst prepared by the coprecipitation method showed the highest NOx conversion. The mechanism by which W modification improved the structure and function of the Ce1Sn2Oy catalyst was systematically investigated by various methods. The corresponding results suggested that Ce-doped tetragonal SnO2 (t-Sn(Ce)O2) was the main active phase in the Ce1Sn2Oy catalyst for the NH3-SCR reaction. The W species regulated the structure by promoting the formation of the t-Sn(Ce)O2 active phase while preventing the generation of the Sn-doped cubic CeO2 (c-Ce(Sn)O2) phase. In addition, the highly dispersed W species on the surface of the Ce1W0.24Sn2Ox catalyst also coupled with Ce species to form new Ce-O-W active sites. The W modification also promoted the ability of the catalysts to oxidize NO to NO2 at 150–300 °C and suppressed the occurrence of excess NH3 oxidation especially at high temperature. The optimal structure and physico-chemical properties induced by W species contributed to superior NH3-SCR performance.

Dual-Functional Tungsten Boosted Lithium-Ion Diffusion and Structural Integrity of LiNi0.8Co0.1Mn0.1O2 Cathodes for High Performance Lithium-Ion Batteries

In this work, a series of LiNi0.8Co0.1Mn0.1O2 oxides with dual-functional heterostructure are acquired from a trace tungsten (W) modification strategy; such a heterostructure contains a gradient tungsten distribution structure and a fast ion-conductive LixWOy coating layer that are in situ formed via thermodynamic diffusion during the calcination process. The gradient doping can increase the lattice parameters because of the large radius of tungsten, then further to expand interlayer spacing and facilitate the lithium-ion diffusion coefficient which can enhance the capacity and rate performance. Besides, the strong W–O bonds can improve the stability of the lattice and promote the structural integrity and thermostability. Meanwhile, the fast ion-conductive LixWOy layer can not only facilitate the rate of Li+ deintercalation, but also act as a defensive layer to suppress side reactions and then improve the cycling property. As a result of the dual-functional heterostructure, the W-modified LiNi0.8Co0.1Mn0.1O2 with the mass fraction of 4500 ppm (W4500) shows a superior discharge capacity of 165.5 mAh g–1 at 5.0 C and an enhanced cycle retention of 88.4% (25 °C) after 100 cycles. Especially, the positive electrode of W4500 delivers a better structural integrity than that of pristine. The investigation elaborates the characters of the dual-functional tungsten modification and offers a path to prepare better Ni-rich layered oxides for lithium-ion batteries.

Adsorptive and Photocatalytic Properties of Tungsten-Modified Titanium Dioxide

We have synthesized oxide composites based on tungsten-modified titanium dioxide and investigated specific features of their formation and their physicochemical, adsorptive, and photocatalytic properties. The results demonstrate that tungsten modification of TiO2 makes it possible to obtain nanopowders (7.2 to 96.7 nm in particle size) with a free specific surface area from 6.4 to 215 m2/g. The synthesized composites have been shown to have considerably higher adsorption capacity and photocatalytic activity (PCA) in comparison to unmodified TiO2 with the same thermal history and Degussa P-25 commercially available titanium dioxide. The materials in which tungsten is incorporated into the crystal lattice of anatase, without tungsten in the form of an individual phase, offer the highest PCA. The electrical conductivity of the composites has been shown to correlate with their PCA.

Regulating the Grain Orientation and Surface Structure of Primary Particles through Tungsten Modification to Comprehensively Enhance the Performance of Nickel-Rich Cathode Materials.

Nickel-rich layered oxides, as the most promising commercial cathode material for high-energy density lithium-ion batteries, experience significant surface structural instabilities that lead to severe capacity deterioration and poor thermal stability. To address these issues, radially aligned grains and surface LixNiyWzO-like heterostructures are designed and obtained with a simple tungsten modification strategy in the LiNi0.91Co0.045Mn0.045O2 cathode. The formation of radially aligned grains, manipulated by the WO3 modifier during synthesis, provides a fast Li+ diffusion channel during the charge/discharge process. Moreover, the tungsten tends to enter into the lattice of the primary particle surface, and the armor-type tungsten-rich heterostructure protects the bulk material from microcracks, structural transformations, and surface side reactions. First-principles calculations indicate that oxygen is more stable in the surface tungsten-rich heterostructure than elsewhere, thus triggering an improved surface structural stability. Consequently, the 2 wt % WO3-modified LiNi0.91Co0.045Mn0.045O2 (NCM@2W) material shows outstanding prolonged cycling performance (capacity retention of 80.85% after 500 cycles) and excellent rate performance (5 C, 188.4 mA h g-1). In addition, its layered-to-rock salt phase transition temperature is increased by 80 °C compared with that of the pristine cathode. This work provides a novel surface modification approach and an in-depth understanding of the overall performance enhancement of nickel-rich layered cathodes.

Defect dipoles inducing the larger piezoelectric properties in BaBi4Ti4−x(Cu0.5W0.5)xO15 ceramics

BaBi4Ti4−x(Cu0.5W0.5)xO15 ceramics with Cu2+ and W6+ co-substitution for the B-site Ti4+ were prepared by using the solid-state reaction process. It was desirable that piezoelectric properties of the BaBi4Ti4−x(Cu0.5W0.5)xO15 ceramics could be improved by inducing the larger lattice distortion with the oxygen vacancy defects neutralized and restrained. Results of the X-ray diffraction analysis confirmed that crystal cell parameter c decreased obviously with the increase in the crystal cell parameter a. Curie temperature, resistivity, and piezoelectric properties of the BBT ceramics are improved by the copper and tungsten modification. The maximum value of piezoelectric coefficient (~ 30 pC/N) can be obtained in the BaBi4Ti4−x(Cu0.5W0.5)xO15 ceramics.

Effect of Tungsten Modification on Zirconium Phosphate-Supported Pt Catalyst for Selective Hydrogenolysis of Glycerol to 1-Propanol

Hydrogenolysis of glycerol to propanols is highly promising for the sustainable development of biomass refining. In this work, the modified amorphous zirconium phosphate (ZrP) supported Pt catalyst...

Promotional effect of tungsten modification on magnetic iron oxide catalyst for selective catalytic reduction of NO with NH3

A novel tungsten-doped magnetic iron oxide catalyst was fabricated for selective catalytic reduction of NOx with NH3 (NH3-SCR), which was supported by carbon-included magnetic materials of Fe2O3–-H synthesized by the solution combustion followed by the oxidization of hydrogen peroxide. As a consequence, the thermal stability of γ-Fe2O3 crystallites located in the magnetic support is significantly enhanced. Meanwhile, the irreversible transformation of Fe2O3 crystallites from γ-phase to α-phase during the annealing process at high temperatures (i.e. 400 °C) is restrained to a large extent. In addition, the magnetic W/Fe2O3 catalyst presents a superb porous structure with higher BET surface area and pore volume due to the anti-sintering effect of tungsten doping on the magnetic Fe2O3. In this regard, the surface acidity as well as the molar ratio of the surface-adsorbed oxygen is substantially augmented, leading to a remarkable improvement of the redox ability of the active bulk species in the catalyst. It is worth mentioning that the promotions in thermal stability and redox ability is affected by the doping amount of tungsten in the catalyst, the molar ratio of glucose/urea/iron, and the ignition temperature for synthesizing the magnetic iron oxide support. The experiments revealed that with a doping amount of 7.5 wt%, a molar ratio of glucose/urea/iron of 5:20:8, and an ignition temperature of 400 °C, the NH3-SCR activity of the novel catalyst could be optimized.

Effect of W on the acidity and redox performance of the Cu0.02Fe0.2WaTiOx (a = 0.01, 0.02, 0.03) catalysts for NH3-SCR of NO

A series of tungsten-modified Cu0.02Fe0.2TiOx catalysts (Cu0.02Fe0.2WaTiOx; a = 0.01, 0.02, and 0.03) was synthesized by sol-gel method. Their catalytic activities were investigated for the selective catalytic reduction (SCR) of NO with NH3, in the presence/absence of 5 vol.% H2O. The characterization techniques of XRD, BET, Raman, H2-TPR, NH3-TPD, XPS, in situ DRIFTS, and kinetic studies were used to reveal the effect of tungsten modification on the redox and acidity of the Cu0.02Fe0.2WaTiOx catalysts. The relationship among the species composition, acid property, and oxidation-reduction behavior of the Cu0.02Fe0.2WaTiOx catalysts was established. Results demonstrated that a moderate amount of tungsten doping can markedly enhance the specific surface area, improve the abundant Brönsted and Lewis acid sites, and tune the surface species composition, which all benefited high-performance catalysis. Water/sulfur resistance also improved because of the excellent acidity levels. Among the Cu0.02Fe0.2WaTiOx catalysts, Cu0.02Fe0.2W0.02TiOx showed the highest NO conversion, a wide reaction-temperature window (235–520 °C) with >90% NO conversion, high N2 selectivity, and high water/sulfur resistance even in the presence of 5 vol.% H2O. Moreover, Cu0.02Fe0.2W0.02TiOx retained its outstanding catalytic activity under a rather high gas hourly space velocity (GHSV) of 100,000 h−1. In conclusion, the combined effects of redox and sufficient acidities on catalytic activity played key roles in superior SCR performance and water/sulfur durability. Furthermore, the NH3-SCR reaction over Cu0.02Fe0.2W0.02TiOx may follow the Eley–Rideal reaction pathway according to the in situ DRIFTS and kinetic studies results.

Improving the electrochemical performance of LiNi1/3Co1/3Mn1/3O2 cathode material via tungsten modification

Poor rate capability and capacity degradation of LiNixCoyMnzO2 restricts its practical commercial applications at high operating voltage (>4.3 V). LiNi1/3Co1/3Mn1/3O2 is successfully modified by tungsten compound through a cost-effective ball-milling and annealing process. The rate capability of W-modified cathode is increased by 57.6% at 10C in 3.0–4.5 V. Moreover, after 100 cycles the capacity retention is improved from 80% to 96% under 0.5C. At 1C, W-modified cathode still maintains 145 mAh g−1 discharge capacity after 100 cycles, which has 16% increase than pristine LiNi1/3Co1/3Mn1/3O2. The improvements on rate and cycle performance are introduced by enhanced Li-ion diffusion and surface stability by tungsten modification.

The Promoting Role of W in Nickel Based Catalyst for Bi-Reforming.

In the present study, co-impregnated tungsten and silver onto nickel based catalysts have been investigated. The influences caused by tungsten modification were inspected by XRD, XPS, TPR and TEM with Elemental Mapping from SEM. the result revealed similarity in terms of physicochemical properties. By adding trace of tungsten subsidiary to silver, it was able to reach as high performance as the catalyst with silver only. The modified catalysts showed enhanced stability and reactivity by forming large Al2O3 structure.

Investigation of surface finishing of carbon based coated tools for dry deep drawing of aluminium alloys

Global trends like growing environmental awareness and demand for resource efficiency motivate an abandonment of lubricants in metal forming. However, dry forming evokes increased friction and wear. Especially, dry deep drawing of aluminum alloys leads to intensive interaction between tool and workpiece due to its high adhesion tendency. One approach to improve the tribological behavior is the application of carbon based coatings. These coatings are characterized by high wear resistance. In order to investigate the potential of carbon based coatings for dry deep drawing, friction and wear behavior of different coating compositions are evaluated in strip drawing tests. This setup is used to model the tribological conditions in the flange area of deep drawing operations. The tribological behavior of tetrahedral amorphous (ta-C) and hydrogenated amorphous carbon coatings with and without tungsten modification (a-C:H:W, a-C:H) is investigated. The influence of tool topography is analyzed by applying different surface finishing. The results show reduced friction with decreased roughness for coated tools. Besides tool topography the coating type determines the tribological conditions. Smooth tools with ta-C and a-C:H coatings reveal low friction and prevent adhesive wear. In contrast, smooth a-C:H:W coated tools only lead to slight improvement compared to rough, uncoated specimen.

A new alloy design concept for austenitic stainless steel with tungsten modification for bipolar plate application in PEMFC

The feasibility of a new alloy design concept utilizing the principle of ‘tungsten bronze effect’ is critically evaluated for the development of metallic bipolar plates for proton exchange membrane fuel cell (PEMFC). An austenitic stainless steel (ASS) is modified with W and La to improve the stability of the passive film in an acidic environment as well as to reduce the contact resistance by the tungsten bronze effect. The experimental ASS containing W and La was evaluated in a simulated PEMFC environment of H 3PO 4 and H 2SO 4 solutions at 80 °C, and the electrical property was evaluated by performing a contact resistance test. The test results show that the ASS modified with W and La has good passive film stability for corrosion resistance and low contact resistance. The X-ray photoelectron spectroscopy (XPS) analysis clearly suggests the possibility of the tungsten bronze effect from the change in valency state of W 6+ to W 5+ in the passive film formed on the modified ASS. The feasibility of a new alloy design concept utilizing the ‘tungsten bronze effect’ is well demonstrated; however, more study is highly required for the development of metallic bipolar plates of PEMFC.

The catalytic activity and methanol tolerance of transition metal modified-ruthenium–selenium catalysts

The activity of ruthenium-based catalysts towards oxygen reduction was enhanced by addition of tungsten, molybdenum and rhodium. The catalysts were produced by decarbonylation of the ruthenium and transition metal carbonyls in the presence of selenium (sulphur) and carbon powders. The produced materials were characterised by scanning electron microscopy and energy dispersive spectroscopy as well as by electrochemical evaluations in both half cells and direct methanol fuel cells. All transition metal-modified catalysts exhibited better performance than those of ruthenium–selenium (sulphur) alone, but the tungsten modification seemed the best approach. The RuSe0.20W0.29 catalyst delivered the maximum power density of up to 40mWcm−2. The improvement is a consequence of the enhanced activity towards oxygen reduction with a minor loss in methanol tolerance as well as a stabilising effect of tungsten on catalysts. The new catalysts were compared to Pt and to sulphur-containing catalysts.

Liquid phase mononitration of chlorobenzene over WO x/ZrO 2: A study of catalyst and reaction parameters

To study the effect of W concentration and activation temperature of the catalysts a series of WO x /ZrO 2 samples with varying concentration of W (10–25 wt.%) were prepared and activated at 650/750 °C. XRD of sample shows 15 wt.% W stabilizes the tetragonal phase of zirconia up to 750 °C. Above and less than 15 wt.% shows peaks corresponding to monoclinic WO 3 and monoclinic ZrO 2, respectively. Further, the tungsten modification stabilizes the specific surface area of ZrO 2. There is an increase in the surface area observed up to 15 wt.% W, which declines on further increase in the concentration. The NH 3 TPD confirms the presence of acid sites with varying strength from the broad desorption profile. The 15 wt.% W and activated at 750 °C shows maximum acidity. The results of the nitration reaction of chlorobezene imply the 15 wt.% W and activation at 750 °C shows maximum activity. Not only yield, a better para-selectivity is also achieved with WO x /ZrO 2 samples. Effect of activation temperature, W concentration and reaction parameters such as reaction temperature, reaction time, the presence of solvent and solvent free medium on activity and selectivity are studied in details.