Vanadium Doping Research Articles

Preparation of NiCo-LDH@NiCoV-LDH interconnected nanosheets as high-performance electrocatalysts for overall water splitting

Alkaline water electrolysis is a promising strategy for the production of hydrogen and oxygen. However, developing high-efficiency non-precious electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge. Here, we report a nickel foam-based electrode coated with NiCoV-LDH and NiCo-LDH nanosheets (denoted as NiCo-LDH@NiCoV-LDH/NF) by a two-step method for efficient water splitting performance. The NiCo-LDH@NiCoV-LDH/NF with unique nanosheet-on-nanosheet construction can enlarge the electrochemical active specific surface area greatly, and thus accelerate the charge transfer of electrocatalytic reactions. Besides, the doping of vanadium could also improve the OER performance. The electrode only requires a low overpotential for OER (260 mV at 100 mA cm−2), and HER (80 mV at 10 mA cm−2) reactions in 1.0 mol/L KOH solution at room temperature. Furthermore, in the two-electrode water splitting test, a current density of 10 mA cm−2 was achieved at 1.55 V using 1.0 mol/L KOH solution, with excellent durability of 40 h. This work provided a facile method for developing new bifunctional catalysts.

Enhanced n-Type conductivity of rutile TiO2 nanowires

This paper reports a solvothermal process to synthesize the rutile TiO2 assisted by the hydrogen reducing atmosphere and vanadium doping technique. The synthesized TiO2 nanowires have a rutile structure with a diameter of about 100 nm and a single crystal growth direction of [01–1]. Moreover, TiO2 nanowires exhibit n-type conductivity with a carrier concentration of 1.87 × 1018 cm−3 and mobility of 1 cm2V−1S−1. The research results show that the n-type conductivity of rutile TiO2 nanowires can be enhanced under the synergistic effect of reducing atmosphere and V doping. The rutile nanowires with good n-type conductivity have bright application in future nano-electronic devices and nano-photoelectric devices.

Design and Synthesis of Vanadium‐Titanium‐Incorporated Mesoporous Silica Catalysts for the Oxidative Dehydrogenation of Propane

AbstractA series of vanadium and titanium‐incorporated mesostructured cellular foams (MCF) silica with different vanadium contents were synthesized by direct hydrothermal method, which applied as catalysts for the oxidative dehydrogenation of propane (ODP). Vanadium doping amount significantly affects the distribution and coordination environment of VOx and TiOx species on the MCF silica. With the increasing of V content, the TiOx species incorporated into silica framework were substituted by some framework V species to form more polymeric or small TiO2 nanoclusters. VOx species were incorporated on both silica surface and TiOx species surface. The interaction between highly dispersed VOx and polymerized TiO2 enhanced the C3H6 formation rate. The 3 V5Ti/MCF catalysts showed the highest propylene productivity (4.2 kgpropylene kgcat−1 h−1, at 500 °C) among the xV5Ti/MCF catalysts because of the highest concentration isolated/oligomeric VOx species incorporated on the appropriate polymerized TiO2 surface.

Effect of vanadium doping on the structural and optical characteristics of nano ZnCdS

Nano Zn0.75-xCd0.25VxS (0 ≤ x ≤ 0.2, step 0.05) samples were formed by the molten salt solid state reaction method at low temperature. Synchrotron x-ray diffraction phase identification revealed biphasic ZnS structure for all samples, cubic zinc blende and hexagonal wurtzite. Rietveld analysis was applied to determine the effect of V-doping on the percentage of each phase and their structural and microstructural parameters. The existence of V ions in the Zn0.75Cd0.25S (ZnCdS) lattice is confirmed by Fourier-transform infrared spectroscopy (FTIR) technique. Utilizing the UV–vis diffuse reflectance spectroscopy, the effect of V-doping on the absorption, reflectance, refractive index, extinction coefficient and electric properties of ZnCdS were studied in detail. The optical bandgap (Eg) significantly decreased from 2.82 eV for zero V-doping to 2.55 eV for x = 0.2. Also, the refractive index decreased sharply in the wavelength region 450–900 nm. ZnCdS sample has anomalous dispersion behavior while the doped samples have anomalous and normal dispersion features. The photoluminescence intensity and emitted colors in the UV and visible regions were affected by the amount of doping.

Phase and crystallinity regulations of Ni(OH)2 by vanadium doping boost electrocatalytic urea oxidation reaction

Direct urea fuel cell (DUFC) and overall urea splitting system have attracted considerable attention as promising choice for energy conversion. Whereas, the anodic half reaction of electrocatalytic urea oxidation reaction (UOR) in these systems awfully limited their practical application due to the complex 6-electron transfer process. Herein, vanadium doped nickel (V-Ni(OH)2) with highly efficient electrocatalytic activity toward UOR was developed by a simple coprecipitation method. The introducing of V not only promotes the phase transforming from inactive β-Ni(OH)2 to highly active α-Ni(OH)2, but also simultaneously modulates the electron environment of Ni, facilitating high valence species Ni3+ generation in low overpotential, enhancing the electrocatalytic activity potent of each Ni3+ site and speeding up the electrocatalytic reaction. The optimal V-Ni(OH)2 catalyst exhibits a summit current density of 241 mA cm−2 at 1.6 V vs. RHE, a Tafel slope of 32.15 mV dec-1, outperforming β-Ni(OH)2 and most catalysts that tested on glassy carbon electrode. Furthermore, the assembled direct urea hydrogen peroxide fuel cell (DUPFC) offers a maximum power density of 13.4 mW cm−2 at 20 °C. This work provides an example of combing phase-regulation and electron modulation method for effective UOR electrocatalysts design.

Effect of vanadium and tungsten doping on the structural, optical, and electronic characteristics of TiO2 nanoparticles

Effect of vanadium and tungsten doping on the structural, optical, and electronic characteristics of TiO2 nanoparticles

Vanadium modified di-bismuth tetra-oxide thin films; synthesis, characterization and properties

Present work reports the structural, photocatalytic, dielectric, optical and antibacterial properties of vanadium doped Bi2O4 thin films synthesized via sol-gel dip coating method. Different functional groups appeared in all samples were identified by FTIR at different wave numbers. X-ray diffraction (XRD) study confirms the presence of monoclinic Bi2O4 phase. Slight change in crystallite size is observed after V doping in Bi2O4 with decrease in lattice parameters. Almost spherical-like morphology was verified by SEM micro-graphs for all the films. UV–VIS–NIR spectrophotometry results display decrement in band gap of Bi2O4 from 2.0 to 1.8 eV for 0–3 wt % of NH4VO3, whereas it increases with the increase in doping from 4-5 wt % of NH4VO3. Moreover, doping enhances photocatalytic properties of Bi2O4. The observed dielectric properties of V-doped Bi2O4 are assumed to stem from vanadium doping. Bi2O4 in the presence of V shows inhibition toward Staphylococcus Aureus (S. Aureus), Pseudomonas Aeruginosa (P. Aeruginosa), Klebsiella Pneumoniae (K. Pneumoniae) and Escherichia Coli (E. Coli). V impurity in the Bi2O4 nanostructure accelerates the power oxidation of Bi2O4 leading to improved antimicrobial activity.

Vanadium-doped indium tin oxide window layer in Sb2Se3 solar cell

Antimony selenide (Sb2Se3) is an emerging photovoltaic material. Indium tin oxide (ITO) is commonly used as the window layer material in Sb2Se3 solar cells; however, ITO films have poor absorption in the near-infrared spectrum. Our objective in this research was to replace conventional ITO with vanadium-doped indium tin oxide (ITO:V) to improve the near-infrared light transmittance of Sb2Se3 thin film solar cells and thereby enhance the efficiency of solar cells. The experiment parameters included vanadium doping concentration and annealing temperature. ITO films doped with 0.35 at.% V and annealed at 100 °C for 30 min outperformed conventional ITO films in terms of photovoltaic performance. The proposed scheme improved light transmittance from 80.03% to 83.02% over a wavelength range of 400–1100 nm, which led to a significant improvement in Jsc and device efficiency (from 4.5% to 5.6%). It appears that ITO films can be doped with vanadium to improve transmittance by reducing refractive index degradation in the near-infrared region.

Effect of doping amount on capacity retention and electrolyte decomposition of LiNi0.5Mn1.5O4-based cathode at high temperature

The long service life of batteries is one of the most desired parameters for the battery industry and end-users. Several doping elements have been proposed to increase discharge capacity, capacity retention, and rate capability of high voltage LiNi0.5Mn1.5O4 (LNMO) cathode. In this study, two different doping elements, i.e., boron (III) and vanadium (IV), are compared to investigate the doping effect on capacity retention of LNMO-electrodes at high temperatures (50 ​°C) and extended cycle performance. Different doping amounts are investigated for comparison, i.e., 1, 3, 5, 7, 10 ​wt% for boron and 10 ​wt% for vanadium. The actual benefit of doping is observed over extended cycle tests (> 1000 cycles) at 50 ​°C and 1C. While pristine LNMO electrodes fail after 80 cycles, 10% B-doped LNMO exhibits the highest capacity retention, 80% at 50 ​°C and 1C after 1200 cycles. The operando differential electrochemical mass spectroscopy results reveal that LNMO electrodes show the highest amount of gas emission (H2 and O2) at ​∼ ​4.7 ​V, where the oxidation of Ni4+/3+ and Ni3+/2+ occurs. Since high amount doping strategy increases Mn3+ amount and, consequently, the charge voltage plateau at ∼4 ​V (Mn3+/Mn4+), this implicitly prevents electrolyte decomposition at high voltage due to decreasing of nickel voltage plateau and less charging step duration at ​∼ ​4.7 ​V. This investigation shows that the cathode life remarkably can be extended by reducing the nickel content with high amount of doping.

Benefits of vanadium doping in Na3MnTi(PO4)3/C as a potential candidate for sodium-ion batteries

Na3MnTi(PO4)3/C is a high-energy sodium-ion battery (SIBs) cathode material. However, the low rate performance and unfavorable cycle life limit its practical applications. Herein, Na3Mn1-xVxTi(PO4)3/C (x = 0, 0.01, 0.05, 0.10) were synthesized by a facile sol-gel method and the performance has been researched via the difference of vanadium doping amount. X-ray diffraction (XRD) indicates that vanadium doping has no obvious effect on the crystal structure. X-ray photoelectron spectroscopy (XPS) and Energy dispersive X-ray spectroscopy (EDS) mapping images show that vanadium has been successfully doped into the material. Cyclic voltammogram (CV) displays obviously three pairs of redox couples, corresponding to the Ti3+/Ti4+, Mn2+/Mn3+ and Mn3+/Mn4+ redox couples, respectively, and is mainly controlled by diffusion and exhibits pseudo-capacitance behavior. The experimental results indicate that vanadium doping can improve the electrochemical performance of Na3MnTi(PO4)3/C, the high specific capacity (116.5 mAh g−1 with a coulomb efficiency of 100% at 0.2C after 100 cycles, 91.8 mAh g−1 higher than that of undoped sample), outstanding cyclability (≈73.6% capacity retention after 500 cycles at 1C, 58.3% higher than that of undoped sample) for Na3Mn0.95V0.05Ti(PO4)3 make the vanadium doping become a promising modification method.

Space charge and trap energy level characteristics of SiC wide bandgap semiconductor

Charge carrier transport and accumulation in silicon carbide (SiC) wide bandgap semiconductors caused by the defect and impurity are likely to lead to serious performance degradation and failure of the semiconductor materials, and the high temperature effect makes the charge behaviors more complex. In this paper, charge carrier transport and accumulation in semi-insulating vanadium doped 4H–SiC crystal materials and the correlated temperature effect were investigated. Attempts were made to address the effect of deep trap levels on carrier transport. A combination of pulsed electro-acoustic direct space charge probing, an electrical conduction·current experiment, and x-ray diffraction measurement was employed. Space charge quantities including trap depth and trap density were extracted. The results show hetero-charge accumulation at adjacent electrode interfaces under a moderate electrical stress region (5–10 kV/mm). The charge carrier transports along the SiC bulk and is captured by the deep traps near the electrode interfaces. The deep trap energy levels originating from the vanadium dopant in SiC crystals are critical to carrier transport, providing carrier trapping sites for charges. This paper could promote the understandings of the carrier transport dynamic and trap energy level characteristic of SiC crystal materials.

Cathode electrochemically reconstructed V-doped CoO nanosheets for enhanced alkaline hydrogen evolution reaction

• The crystalline V-doped CoO nanosheets were obtained by cathode electrochemical reconstruction of amorphous VCoO. • The crystallineV-doped CoO exhibited better HER active than amorphous VCoO. • Nanosheets structure could provide abundant active sites. • Vanadium doping effectively increased the intrinsic activity of CoO (1 1 1) and the number of active sites. • The V-doped CoO nanosheets display superb performance for HER at high potential. In the search for nonprecious metal catalysts to achieving active industrial hydrogen evolution reaction (HER), transition metal oxides (TMOs) have been proposed as promising candidates. In various synthetic methods for preparation of TMO electrocatalysts, electrochemical reconstruction, as one of the most efficient and controlled way, attracts much attentions. However, most of reported electrochemical reconstruction is usually carried out on the surface of anode via electrochemical oxidation reaction, and the investigations of cathode electrochemical reconstruction are rarely reported. Here, V-doped CoO nanosheets (V-CoO) are successfully prepared via cathode electrochemical reconstruction of amorphous VCoO. The reconstruction process and principle are studied in detail. Compared with the previous oxides, the obtained V-CoO possesses the promoted HER performance with overpotential of 280 mV at − 100 mA cm −2 and superior durability at − 1.07 V vs. RHE for 20 h. DFT calculations further reveals that vanadium doping effectively improves the intrinsic activity of oxides and HER active sites located at Co side of V-CoO (1 1 1) facet is the favorable H* adsorption site of reconstructed oxides. This work highlights the importance of electrochemical reconstruction on cathode to improve the HER activity of TMOs.

Synthesis of one-dimensional vanadium-doped CoS/Co9S8 heterojunctions as bifunctional electrocatalysts for zinc-air battery

Cobalt-based electrocatalysts have been considered promising materials for the oxygen evolution reaction (OER). Herein, we now report the synthesis of vanadium-doped CoS/Co9S8 heterostructures embedded on carbon nanorods (V-CoS/Co9S8@CNR), which was realized through one-step sulfurization of Zeolitic Imidazolate Framework-67 (ZIF-67) grown on V2O5 nanorods (V2O5@ZIF-67). The results of experiment and theoretical calculation verified that because of the vanadium dopant and the coupled nanointerface that can expedite the synergistic effect of Co9S8 and CoS, the obtained V-CoS/Co9S8@CNR showed an excellent OER catalytic performance (269 mV@10 mA/cm2) and comparable ORR catalytic performance. The assembled rechargeable Zn-air batteries displayed a superior performance as well as high charging–discharging cycling stability (>200 h) with a slight increase in the voltage gap.

Suppression of anisotropy of kinetic energy in doped vanadium perovskites by charged defects and spin–orbital polarons

We study the interplay of rotations of t2g-orbitals in vanadium perovskites such as La1−xSrxVO3 induced by spin–orbital polarons and by charged defects. We also analyze the resulting decay of orbital order as well as the suppression of anisotropy of kinetic energy on varying the doping. The strong local correlations and the superexchange interactions are modeled by an extended 3-orbital-flavor Hubbard–Hund model. Because of the charged defects, it is crucial to extend the model by long-range Coulomb defect potentials as well as by long-range electron–electron repulsion. Thereby, the resulting binding of doped holes (i.e., spin–orbital polarons) to negative defects leads to screening by effective dynamic dipoles. The resulting dipolar fields, in combination with disorder, control the defect states and form a soft Coulomb gap inside the Mott–Hubbard gap and thereby control the low-energy properties of the system.

Vanadium doped nickel hydroxide nanosheets for efficient overall alkaline water splitting

Developing bifunctional electrocatalysts with high efficiency and low cost for overall water splitting at large current densities is of great value for industrial application, yet remains challenge. Herein, hetero-atom doping is adopted as the effective strategy to boost catalysis performances. Vanadium elements are doped into nickel hydroxide via a hydrothermal method to improve oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysis performance. XPS spectra reveal that vanadium dopants not only tune the chemical state of Ni, but also serve as promotor during the catalysis. SEM and TEM characterizations show the nanosheets assembled architecture, which provides structure advantages of easily accessible active sites and accelerates charge transfer. Electrochemical tests indicate that V-doping results in improved active sites and enhanced kinetics. The as-prepared V doped Ni(OH)2 nanosheets grown on nickel foam (V–Ni(OH)2/NF) display advanced electrocatalysis performances for both OER and HER. To reach high current densities of 100 and 400 mA cm−2, the V–Ni(OH)2/NF only needs low overpotentials of 275 and 476 mV for OER and 254 and 493 mV for HER. A two-electrode electrolyzer using V–Ni(OH)2/NF as bifunctional catalyst exhibits low cell voltages of 1.58 and 1.84 V at current densities of 100 and 400 mA cm−2 for overall water splitting in alkaline solution.

Deformation of 4H-SiC: The role of dopants

The role of dopants on deformation and mechanical properties of 4H silicon carbide (4H-SiC) is proposed by using nanoindentation. It is found that the hardness, elastic modulus, and fracture toughness of 4H-SiC substrate wafers all decrease on the order of vanadium (V) doping, undoping, and nitrogen (N) doping. For all three types of 4H-SiC, basal plane dislocations (BPDs), threading edge dislocations, and cracks are formed during the nanoindentation. Polymorph transitions from 4H-SiC to amorphous SiC and 3C-SiC are found as the penetration depth of the indent increases from the subsurface to the deeper region. N doping is found to weaken the bond strength of 4H-SiC, which enhances the glide and piling up of BPDs in nanoindentated N-doped 4H-SiC. In contrast, V doping effectively hinders the glide of BPDs, which accumulates a high-stress field and facilitates the polymorph transition from 4H-SiC to 3C-SiC and amorphous SiC. The insight on the effects of dopants on the deformation and mechanical properties of 4H-SiC may help the design of the processing of differently doped 4H-SiC substrate wafers.

Effect of vanadium doping on the thermoelectric properties of MoS2

Recently, MoS2 has been considered as a promising economic and nontoxic thermoelectric material due to its low thermal conductivity and high Seebeck coefficient. However, the poor intrinsic electrical conductivity is still a main obstacle for its wide scale application. Here, we have successfully synthesized p-type V doped MoS2 and systematically investigated the influence of V doping on the thermoelectric properties of MoS2. In the whole doping range, the samples always keep a perfect hexagonal structure. The doped V atoms behave as acceptors and improve the carrier concentration by three to five orders of magnitude, thereby enhancing the electrical conductivity remarkably. In addition, V doping promotes grain refinement and introduces numerous point defects, which play a synergistic role in reducing lattice thermal conductivity. Due to the layered microstructure, obvious anisotropy was observed in the transport properties of VxMo1-xS2. Compared with that of pristine MoS2 (ZTmax = 0.013 at 860 K), the maximum ZT value of VxMo1-xS2 has been increased to 0.24 at 860 K.

Antibacterial activity of V- doped rod-like MgO crystals decorated with nanoflake layer

In present study, we report a V doping fabrication method for obtaining rod-like MgO crystals decorated with a nanoflake layer. This novel structure has only been minimally reported in literature. Pure MgO and Mg2V2O7–MgO composite materials were obtained by precipitation and impregnation methods, with vanadium added concentrations of 0–9%. The influence of V doping on crystal structure and particle morphology of MgO was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis demonstrated that MgO has a cubic structure, while X-ray photoelectron spectroscopy (XPS) revealed that V5+ exists on the surface of MgO. The specific surface areas and pore sizes of MgO composites were calculated by BET and BJH analysis. These techniques revealed that specific surface area and pore size of MgO increased due to vanadium doping. The antibacterial effects of Mg2V2O7–MgO composite materials against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were assessed using a bacterial killing/colony-forming unit (CFU) assay and bacteriostatic ring method. Our results demonstrate that V doping dramatically improved antimicrobial properties of MgO, with 7 mol% doping inducing the best antibacterial activity. The antibacterial mechanisms of Mg2V2O7–MgO composite material were also proposed.

Controlled transformation of V-doped Co(OH)2 hexagonal nanosheets towards enhanced electrochemical performance

To meet the energy demands, development of efficient electrode materials or structures for electrochemical energy storage systems are highly desired. Hence, novel hexagonal nanosheets of vanadium doped Co(OH)2 have been synthesized by cost effective hydrothermal-method, which exhibited excellent electrochemical performance. The structural characterizations were performed by XRD, FESEM, EDS and TEM tools, which confirmed the phases purity and perfect hexagonal based nanosheets. It was also revealed that with the increase in doping concentration of vanadium, the morphology was gradually transformed from hierarchical structures to hexagonal nanosheets. CV results exhibited that the specific capacitance was increased on vanadium doping and maximum capacitance of 1357 F/g was obtained for 15% V-doped Co(OH)2 sample, which is almost two times greater than undoped-Co(OH)2. Furthermore, this sample has shown a very high capacitance retention of 89% over 3000 CV cycles. These improvements are attributed to the optimized hexagonal nanosheets based morphology and appropriate doping value of redox active element i.e. vanadium into Co(OH)2. This V-doping affected the shape of nano structures along with changes in redox reactions of Co(OH)2.

Synthesis of sponge like Gd3+ doped vanadium oxide/2D MXene composites for improved degradation of industrial effluents and pathogens

Current report is based on the synthesis of Gd +3 doped V 2 O 5 nanostructures (GVO) along with fabrication of GVO/MXene binary nanocomposite. As synthesized GVO and GVO/MXene were characterized by XRD (X-ray diffraction), FESEM (Field emission scanning electron microscopy), EDX (Energy dispersive X-ray), BET (Brunauer Emmett Teller technique) and UV–Visible spectroscopy. Diffraction and elemental analysis confirmed the substitution of Gd +3 ions in VO layers. Orthorhombic phase of VO was observed in both GVO and GVO/MXene samples with crystallite size range of 17.02–17.51 nm. FESEM analysis indicated asymmetrical VO particles and sheets distributed on MXene layers, giving out a sponge like appearance. Surface area of GVO and GVO/MXene was enhanced to 20.46 and 23.69 nm, respectively. Effect of Gd +3 contents was significant on optical properties, which reduced the band gap energy of VO to 2.33 eV. The photocatalytic performance of prepared samples was analysed by the degradation of Methylene blue (MB) under direct sunlight. Gd +3 ion doping was found useful to enhance degradation of MB up to ∼71%. Among all samples, GVO/MXene showed maximum degradation (∼92%) within 120 min. Meanwhile, GVO/MXene showed good recyclability for successive five cycles. In addition, GVO and GVO/MXene were effective antibacterial agents against Gram positive (S. aureus) and Gram negative (P. vulgaris) strains of bacteria. The results suggested that the GVO and GVO/MXene could serve as potential candidates for large scale treatment of organic pollutants and pathogens.