Vanadium Oxidation Research Articles

Low temperature synthesis of VO2 and hysteresis free VOx thin films with high temperature coefficient of resistance for bolometer applications

Vanadium dioxide (VO2) is an insulator to metal phase transition material, which finds many electronic and optical applications due to its reversible switching while VOx-based bolometers are widely used in commercial uncooled infrared detectors due to their high-temperature coefficient of resistance and low resistivity. Atmospheric pressure thermal oxidation (APTO) of Vanadium (V) is a simple process used to synthesize VO2 films without the need for precise control of oxygen partial pressure unlike other synthesis methods. In this work, we report the effect of reducing the V oxidation temperature to 250–450 °C during APTO and synthesize films with different oxidation durations. For an optimized oxidation duration at each oxidation temperature, VO2 films are obtained with more than two orders of resistance switching. This optimum oxidation duration is found to decrease exponentially with increase in oxidation temperature with an activation energy of 1.05 eV. The phase transition temperature of these VO2 films is found to decrease monotonically with decrease in oxidation temperature. We also observe that partially oxidized (oxidation time less than optimized oxidation duration to form VO2) VOx films show broad resistance switching from room temperature up to 70 °C instead of steep switching at the phase transition temperature. The partially oxidized film shows a temperature coefficient of resistance (TCR) as high as ∼10%/K, which is 3–4 times greater than TCR of commercial VOx thin films used in bolometers while showing similar resistivity. The resistivity of these films also exhibits almost zero hysteresis with temperature, an important requirement for bolometer applications. This study will widen the usefulness of the APTO process for fabricating VO2-based devices and high TCR VOx films for bolometer applications. The demonstrated low temperature process will especially be suitable to integrate VO2/VOx on substrates which can sustain only low temperatures such as some of the flexible substrates.

Charge and Solvent Effects on the Redox Behavior of Vanadyl Salen-Crown Complexes.

The incorporation of charged groups proximal to a redox active transition metal center can impact the local electric field, altering redox behavior and enhancing catalysis. Vanadyl salen (salen = N,N'-ethylenebis(salicylideneaminato)) complexes functionalized with a crown ether containing a nonredox active metal cation (V-Na, V-K, V-Ba, V-La, V-Ce, and V-Nd) were synthesized. The electrochemical behavior of this series of complexes was investigated by cyclic voltammetry in solvents with varying polarity and dielectric constant (ε) (acetonitrile, ε = 37.5; N,N-dimethylformamide, ε = 36.7; and dichloromethane, ε = 8.93). The vanadium(V/IV) reduction potential shifted anodically with increasing cation charge compared to a complex lacking a proximal cation (ΔE1/2 > 900 mV in acetonitrile and >700 mV in dichloromethane). In contrast, the reduction potential for all vanadyl salen-crown complexes measured in N,N-dimethylformamide was insensitive to the magnitude of the cationic charge, regardless of the electrolyte or counteranion used. Titration studies of N,N-dimethylformamide into acetonitrile resulted in cathodic shifting of the vanadium(V/IV) reduction potential with increasing concentration of N,N-dimethylformamide. Binding constants of N,N-dimethylformamide (log(KDMF)) for the series of crown complexes show increased binding affinity in the order of V-La > V-Ba > V-K > (salen)V(O), indicating an enhancement of Lewis acid/base interaction with increasing cationic charge. The redox behavior of (salen)V(O) and (salen-OMe)V(O) (salen-OMe = N,N'-ethylenebis(3-methoxysalicylideneamine) was also investigated and compared to the crown-containing complexes. For (salen-OMe)V(O), a weak association of triflate salt at the vanadium(IV) oxidation state was observed through cyclic voltammetry titration experiments, and cation dissociation upon oxidation to vanadium(V) was identified. These studies demonstrate the noninnocent role of solvent coordination and cation/anion effects on redox behavior and, by extension, the local electric field.

On the Symmetry, Electronic Properties, and Possible Metallic States in NASICON-Structured A4V2(PO4)3 (A = Li, Na, K) Phosphates.

In this work, the electronic structure and properties of NASICON-structured A4V2(PO4)3, where A = Li, Na, K were studied using hybrid density functional theory calculations. The symmetries were analyzed using a group theoretical approach, and the band structures were examined by the atom and orbital projected density of states analyses. Li4V2(PO4)3 and Na4V2(PO4)3 adopted monoclinic structures with the C2 space group and averaged vanadium oxidation states of V+2.5 in the ground state, whereas K4V2(PO4)3 adopted a monoclinic structure with the C2 space group and mixed vanadium oxidation states V+2/V+3 in the ground state. The mixed oxidation state is the least stable state in Na4V2(PO4)3 and Li4V2(PO4)3. Symmetry increases in Li4V2(PO4)3 and Na4V2(PO4)3 led to the appearance of a metallic state that was independent of the vanadium oxidation states (except for the averaged oxidation state R32 Na4V2(PO4)3). On the other hand, K4V2(PO4)3 retained a small band gap in all studied configurations. These results might provide valuable guidance for crystallography and electronic structure investigations for this important class of materials.

Surface Oxidation State Variations and Insulator–Metal Transition Modulations in Vanadium Oxides with Pulsed Hydrogen Plasma

AbstractSurface often determines the formation and function of nanoscale thin films and nanomaterials. In correlated vanadium oxides, oxidation states and stoichiometry play important roles in regulating reversible insulator–metal transition (IMT) behaviors. This study presents the surface oxidation state reductions and IMT modulations in vanadium oxides. Oxidation states of vanadium in the surface layer are changed in the nanostructures of vanadium oxides through pulsed hydrogen plasma (PHP). The thickness‐dependent variations are also observed with Raman and X‐ray photoelectron spectroscopy (XPS), and verified in vanadium oxides with different oxidation states. Obvious modulations on IMT behaviors are then demonstrated and related to such variation of surface oxidation states in the VO2 thin film and nanobeam. It is expected that such surface manipulations are beneficial to a better understanding of the IMT in correlated vanadium oxides and the fabrication of advanced functional electronic and photoelectronic devices.

Insight into the oxidation mechanisms of vanadium slag and its application in the separation of V and Cr

Vanadium slag contains valuable element vanadium and heavy metal element chromium. V and Cr in the traditional oxidation roasting process were simultaneously oxidized by oxidant O2 in the air, which made the separation of V and Cr difficult, and produced highly toxic Cr6+ that polluted seriously the environment. The valence states of Fe, Cr and V in vanadium slag increased during oxidation roasting. In order to reveal the oxidation mechanisms, the oxidative roasting of Na2CO3–Cr2O3, Na2CO3–FeCr2O4 and Na2CO3–V2O3 was investigated. The results showed that Cr2O3 could be oxidized by O2 and the presence of Fe2+ reduced the oxidation ratio of Cr3+. Moreover, it was found for the first time that the V3+ could be oxidized by CO2. The calculation of FactSage 8.0 showed that V2O3 could be oxidized by Na2CO3. However, V2O3 could not be directly oxidized to VO2 or V2O5 by CO2. Due to the lack of NaVO2 data in the thermodynamic database, the reaction of NaVO2 and CO2 was firstly simulated by Vienna ab initio simulation package (VASP). The results indicated that NaVO2 could be oxidized by CO2. On the basis of revealing the oxidation mechanisms of V, Cr, and Fe, an innovative method for selective oxidation of vanadium by oxidant CO2 was proposed. The extraction ratio of vanadium could reach 90.5% at 800 °C, in which the mass ratio of V/Cr was 32,400. Mass ratio of V/Cr in this work was 1448 to 20,250 times larger than that in the literatures. Based on the high vanadium extraction ratio, the problems of separation of V and Cr and the presence of Cr6+ were solved from the source. This novel discovery may provide an inspiration for the vanadium metallurgical revolutionary.

Ecotoxicity stress and bioaccumulation in Eisenia fetida earthworms exposed to vanadium pentoxide in soil

As an important commercial form of vanadium, vanadium pentoxide (V2O5) is widely used in various modern industries, and its environmental impacts and ecotoxicity have been extensively studied. In this research, the ecotoxicity of V2O5 to earthworms (Eisenia fetida) in soil was tested by exposure to V2O5 at a series of doses, and biochemical response indices, such as the superoxide dismutase (SOD) and catalase (CAT) enzyme activity and malondialdehyde (MDA) content, were analysed to determine the mechanism by which antioxidant enzymes respond to V2O5 exposure. The bioaccumulation factor (BAF) of vanadium pentoxide in the earthworms and soil was also measured to explore the bioaccumulation process of V2O5 in the test period. The results showed that the acute and subchronic lethal toxicity values of V2O5 towards E. fetida were 21.96mg/kg (LC50, 14days) and 6.28mg/kg (LC10, 28days), respectively. For the antioxidant enzymes, SOD and CAT were synchronously induced or inhibited within the time period, and the enzyme activity had a dose-effect relationship with the V2O5 concentration. MDA analysis indicated that lipid peroxidation in earthworms mainly occurred at the early stage and was eliminated slowly in the later stage during the test time. In addition, the BAFs were much less than 1, which indicated that V2O5 did not easily accumulate in earthworms, and the BAF was positively correlated with the exposure time and negatively linearly correlated with the V2O5 concentration in the soil. These results indicated that the bioconcentration and metabolic mechanism of V2O5 in earthworms differed with the different exposure concentrations, and bioaccumulation became balanced after 14-28days in earthworms exposed to a relatively lower dose of V2O5. The analysis of the integrated biomarker response (IBR) index indicated that the trends of IBR values were positively related to the changing V2O5 concentration, and the IBR index could reflect the organism's sensitivity to the external stimulus of V2O5. The toxicity of V2O5 is mainly caused by V5+, which is also an important factor in formulating guidelines regarding vanadium levels in soil, and the test earthworm species (Eisenia fetida) is a sensitive biological indicator for risk assessments of vanadium oxidation in the soil.

Selective oxidation of vanadium from vanadium slag by CO2 during CaCO3 roasting treatment

In order to reduce CO2 emission during utilization of solid vanadium slag, a novel and cleaner method for selective oxidation of vanadium by oxidant CO2 was proposed. The extraction ratio of V increased from 83.1 % to 93.2 % with increasing temperature from 800 °C to 1000 °C. The conversion ratio of CO2 to CO in the CaCO3-vanadium slag was 23.3 % at 800 °C. The roasting of CaCO3-Cr2O3, CaCO3-V2O3 and CaCO3-vanadium slag were investigated and the gases produced in the roasting were analyzed by gas chromatography. Thermodynamic calculations showed that V2O3 and VO2 in the presence of CaCO3 at 800 °C, 900 °C, and 1100 °C could be oxidized to Ca3V2O8. Due to lack of CaV2O4 data in the thermodynamic database, the reaction of CaV2O4 and CO2 was firstly simulated by Ab initio molecular dynamics. The results indicated that CaV2O4 could be oxidized by CO2 and CO gas was produced. This novel roasting process can further achieve effective and green utilization of vanadium slag.

Defect engineering on VO2(B) nanoleaves/graphene oxide for the high performance of cathodes of zinc-ion batteries with a wide temperature range

Designing cathodes with long service life, remarkable rate capability and all-climate workable is crucial to improve the performance of aqueous zinc-ion batteries (AZIBs). Herein, we constructed a vanadium dioxide/graphene oxide (VO2(B)/GO) sample that combines VO2 with GO through hydrothermal route and can simultaneously provide rate capability. VO2(B)/GO is rich in oxygen vacancies, which weakens the electrostatic force, and GO prevents vanadium oxidation. Density functional theory (DFT) calculations elucidate oxygen vacancies can offer more storage sites with increased reaction kinetics. The electrode exhibited a high reversible capacity of 423 mAh g−1 at 0.5 A g−1 and preserved long-life cycling properties at 15 A g−1. The presence of oxygen vacancies and GO can contribute to the excellent performance and prevent the structure of VO2 from collapsing during cycling. We successfully lit up commercial light-emitting diode (LED) lights with a VO2(B)/GO electrode. In addition, VO2(B)/GO exhibits excellent performance in all-climate conditions (-15-60 °C). This combinatorial design strategy provides a broadly applicable approach for durability and all-climate workable batteries.

Vanadium as co-catalyst for exceptionally boosted Fenton and Fenton-like oxidation: Vanadium species mediated direct and indirect routes

In this study, vanadium powder (V) was employed as a cocatalyst to enhance the Fenton-like system. The V-Fe(III)/H2O2 system can rapidly produce hydroxyl radicals and completely oxidize chloramphenicol with exceptionally high stability for long-term operation. The low-valent vanadium sites on the surface during the stepwise oxidation of vanadium from V0 to V(IV) can donate electrons for direct H2O2 activation and indirect Fenton reaction by reducing Fe(III) to produce hydroxyl radicals. Meanwhile, density functional theory (DFT) calculation unveils that low-valent vanadium sites of vanadium can lengthen Fe-O bonds of FeOH2+ to elevate the oxidation potential of Fe(III) and promote Fe(III) reduction induced by H2O2. The self-cleaning effect of vanadium under acidic conditions can maintain reactive sites for sustainable electron donation and long-lasting enhanced Fenton oxidation. This study provides a novel enhanced Fenton oxidation for water remediation and the first mechanistic insights into the origins of V-based advanced oxidation technologies, it may also be beneficial to treat vanadium-contained wastewater.

From the Irreversible Transformation of VO2 to V2O5 Electrochromic Films.

Since its discovery, electrochromism, known as the modulation of optical properties under an applied voltage, has attracted strong interest from the scientific community and has proved to be of significant utility in various applications. Although vanadium dioxide (VO2) has been a candidate for extensive research for its thermochromic properties, its intrinsic electrochromism has scarcely been reported so far. In this study, multi-electrochromism is described for VO2 thick films. Indeed, a VO2 opaque film, doctor bladed from homemade monoclinic VO2 powder, shows a pronounced color modulation from orange to green and blue associated with an amorphization-recrystallization phenomenon upon cycling in a lithium-based electrolyte. The strong memory effect allows us to follow the coloration mechanism by combining various ex situ and in situ characterizations addressing both structural and electronic aspects. Upon cycling, the multichromism of VO2 finds its origin in the transformation of VO2 into orange V2O5 upon oxidation, while in reduction, the blue lithiated state illustrates a mixed vanadium oxidation state.

Electronic Structure Evolution from Metallic Vanadium to Metallic VxOy: A NAPPES Study for O2 + V Gas–Solid Interaction

Gas–solid interactions between molecular oxygen and metallic vanadium surfaces and the systematic evolution in the electronic structure of vanadium oxide (VOx) surfaces have been explored in the present work by near-ambient pressure photoelectron spectroscopy (NAPPES). The current article studies the evolution of various oxides of vanadium as a function of partial pressure of O2 (ultrahigh vacuum to 1 mbar), temperature (298–875 K), and the exposure time to oxygen (up to 18 h). Valence-band (VB) and core-level spectral measurements recorded with UV (He–I = 21.2 eV) and Al Kα (1486.6 eV) photons, respectively, show interesting changes. (1) Oxidation is limited to the top layers of vanadium at 298 K and up to a partial pressure of 1 mbar O2. About 50% of vanadium gets oxidized, and the remaining amount exists as metal within the top 10 nm. (2) Metallic vanadium disappears above 625 K, and it is predominantly oxidized to a mixture of V4+ and V5+ oxidation states at a 0.1 mbar partial pressure of O2. Points 1 and 2 suggest the predominantly thermodynamically controlled nature of vanadium oxidation through oxygen diffusion into the subsurface and bulk layers. (3) The Fermi-level (EF) feature observed first at ≥725 K at a 0.1 mbar O2 pressure demonstrates the formation of metallic VO2; however, its metallic nature is preserved even at ambient temperature due to interweaving nanodomains of VOx with VO2. (4) Only partial conversion of surface layers to V5+ (V2O5) along with VO2 and V2O3 (within the probing depth of 8–10 nm by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS)) was observed even after prolonged heating (18 h) in 1 mbar O2 pressure. (5) The nature of the surface changes between metal and semiconducting/insulator oxides is substantiated by the observation of changes in work function (ϕ) and EF features. Typical VB features and Fermi intensity of V-metal and vanadium oxides were observed, and the results were corroborated with core-level and VB spectra. The present results extend the capabilities of NAPPES to explore the electronic structure evolution as a function of reaction conditions and underscore its relevance to areas such as heterogeneous catalysis and sensing.

High efficient vanadium extraction from vanadium slag using an enhanced acid leaching-coprecipitation process

Vanadium slag (VS) is a by-product of vanadium titanium magnetite BOF steelmaking process and becomes an important material for vanadium products preparation. Sodium roasting-water leaching is a mainstream process for industrial production, but the water leaching residue (WLR) usually remains 1.0 wt% to 3.0 wt% V2O5, which still has value for recycling extraction of vanadium. In this research, a two-stage leaching process was proposed for high efficient vanadium extraction. The first stage leaching was sodium roasting-water leaching for vS and the second stage leaching was sulfuric acid leaching for WLR. As a result, the total leaching efficiency of vanadium can reach as high as 98.52%, which was 7.72% higher than that of conventional water leaching efficiency of vanadium (90.80%). The mechanism analysis indicates that the CaNaFe2Si4O12 and NaFeSi2O6 water-insoluble phases formed and covered on (Mn,Fe)(V,Cr)2O4 spinel surface during roasting, hindering vanadium oxidation and dissolution. The structures of wrapping phases and spinel can be effectively destroyed by acid leaching, releasing vanadium in WLR. By using hydrolytic precipitation of iron ions in acid leachate, 99.78% of vanadium can be recovered as V-Fe precipitation slag, which contains 6.83 wt% V2O5 and can be cycled back to sodium roasting process. The V-Fe slag belongs to amorphous precipitation, illustrating that residual vanadium in WLR can be changed to unstable compound by acid leaching and hydrolysis precipitation, which makes vanadium easier to extract during sodium roasting-water leaching process. This research has the advantages of enhanced reuse of V resource in the WLR, achieving a high V recovery. The short process has a strong adaptability and can provide technical support for efficient V extraction from vS.

Simply Prepared Magnesium Vanadium Oxides as Cathode Materials for Rechargeable Aqueous Magnesium Ion Batteries.

Vanadium-oxide-based materials exist with various vanadium oxidation states having rich chemistry and ability to form layered structures. These properties make them suitable for different applications, including energy conversion and storage. Magnesium vanadium oxide materials obtained using simple preparation route were studied as potential cathodes for rechargeable aqueous magnesium ion batteries. Structural characterization of the synthesized materials was performed using XRD and vibrational spectroscopy techniques (FTIR and Raman spectroscopy). Electrochemical behavior of the materials, observed by cyclic voltammetry, was further explained by BVS calculations. Sluggish Mg2+ ion kinetics in MgV2O6 was shown as a result of poor electronic and ionic wiring. Complex redox behavior of the studied materials is dependent on phase composition and metal ion inserted/deinserted into/from the material. Among the studied magnesium vanadium oxides, the multiphase oxide systems exhibited better Mg2+ insertion/deinsertion performances than the single-phase ones. Carbon addition was found to be an effective dual strategy for enhancing the charge storage behavior of MgV2O6.

Chemically lithiated layered VOPO4 by a microwave-assisted hydrothermal method and its electrochemical properties in rechargeable Li-ion batteries and supercapacitor applications

Lithium vanadyl phosphate (LiVOPO4) is a derivative of vanadyl phosphate (VOPO4) with different polymorphs that can be obtained based on employed synthesis approach. LiVOPO4 has recently gained attention due to multielectron electrochemical properties that result from varying vanadium redox activities as electrodes for lithium-ion batteries. In this work, we obtained single crystalline tetragonal layered LiVOPO4 (LVOP) by Li intercalation into solvothermal synthesized polycrystalline tetragonal layered VOPO4.2H2O (VOP) by a microwave-assisted hydrothermal method. We found that intercalation of Li+ into layered VOP resulted in a decrease in the interlayer spacing from 0.726 nm to 0.449 nm as well as a reduction of the vanadium oxidation state (+5 to +4), which resulted in a decrease of the band gap. Electrochemical properties of LVOP were evaluated as both a cathode and an anode in a half-cell lithium-ion battery system. The electrode used as a cathode, demonstrated a high capacity of 265 mAhg−1 at 0.1 C as well as 77 mAhg−1 at a high rate of 2 C. When used as an anode, the material exhibits an initial capacity of 865 mAhg−1 at 0.1 C. The electrode demonstrated good rate capability by maintaining a high capacity of 220 mAhg−1 at a high rate of 10 C. We also demonstrated for the first time that VOP can be utilized as a working electrode in an aqueous-based three-electrode supercapacitor and shows good capacitance properties.

Investigating Electrode Reactions in Vanadium Redox Flow Batteries - a Distribution of Relaxation Times Analysis

Due to the increasing energy demand worldwide and the urgency of action because of climate change, new energy storage devices are needed to balance the fluctuations of renewable energy sources. The Vanadium Redox Flow Battery (VRFB) is a promising technology for large-scale energy storage but still needs to overcome significant lifetime and efficiency challenges, which are decreased by polarization losses during operation. It is essential to conduct experiments in a setup that closely mimics the cell's operating conditions to analyze the ongoing processes in a VRFB. Therefore, setups reflecting a half cell are well-suited. Thus, new insights into the reaction and transport processes in a VRFB can be gained. Electrochemical Impedance Spectroscopy (EIS) combined with Distribution of Relaxation Times (DRT) analysis is a well-suited method to investigate electrode reactions. This combination of methods is frequently used in research for lithium-ion batteries or in our group for fuel cell characterization (1-3). To the best of our knowledge, there is no study using EIS and DRT analysis to analyze processes in a model half cell in VRFB research published yet, and just very few studies on characterization in full cell-like setups are available (4). Here, we present a novel 3D printed flow cell for investigations under application-oriented conditions, designed to ensure steady-state conditions during the measurements. These studies focus on the characterization of the processes in the positive half cell by EIS to deepen the knowledge about the polarization losses in VRFBs.The vanadium-containing electrolyte is continuously pumped through the cell during the experiments to guarantee consistent conditions while EIS measurements are performed. The electrolyte flows through the carbon paper stack used as electrode material, undergoing an electrochemical reaction. Here, either the oxidation of vanadium(IV) to vanadium(V) or the reduction from vanadium(V) to vanadium(IV) occurs. The recorded data were analyzed with the DRT method, which allows the separation of physicochemical processes on different time scales. Parameters like the temperature, the flow rate, the electrolyte concentration, and the electrolyte species were varied independently to identify the individual processes in the positive half cell of a VRFB.This setup enables electrochemical impedance measurements of high quality, which is essential for a reliable DRT analysis. We could assign the peaks in the DRT spectrum to the electrochemical reaction, the convective transport through the electrode structure, and the diffusion processes of the vanadium species. Thus, we could identify the individual processes in the positive half cell of the VRFB and their contributions to the overall impedance. This information is vital in search of optimized operating conditions with reduced polarization losses.1. M. A. Danzer, Batteries, 5(3), 53 (2019).2. A. Weiß, S. Schindler, S. Galbiati, M. A. Danzer and R. Zeis, Electrochimica Acta, 230, 391–398 (2017).3. N. Bevilacqua, M. A. Schmid and R. Zeis, Journal of Power Sources, 471, 228469 (2020).4. J. Schneider, T. Tichter, P. Khadke, R. Zeis and C. Roth, Electrochimica Acta, 336, 135510 (2020). Figure 1

Electro-Catalytic Reduction of Nitrogen to Ammonia By Vanadium Oxide and Vanadium Oxynitride Thin Films: The Roles of Metal Oxophilicity, and Lattice Oxygen and Nitrogen Towards NRR

Electro-catalytic reduction of N2 to NH3 using Earth-abundant oxide and oxynitrides is an energy- and environmentally-friendly alternative to the Haber-Bosch process. The present contribution summarizes our recent progress on vanadium oxide (VO) and vanadium oxynitride (VON) thin films1,2 as electrochemical nitrogen reduction reaction (NRR) catalysts at neutral pH conditions. In the case of VO films, the N-free VIII/IV-oxide, created by O2 plasma oxidation of polycrystalline vanadium, exhibited N2 reduction at an onset potential of -0.16 V vs. Ag/AgCl. DFT calculations indicated that N2 scission from O-supported V-centers is energetically favorable by ~18 kcal/mole as compared to N-supported sites. Interestingly, in the case of VON catalysts, both electrochemistry and photoemission data revealed the involvement of both lattice N and dissolved N2 in the NRR process. Our results also show that NH3 production from VON lattice N occurs in the presence or absence of N2 and involves the formation of V≡N: intermediates or similar unsaturated VN surface states. This is in contrast to VO where N2 reduction occurred in the presence or absence of lattice N, and without N incorporation into a vanadium oxide lattice. Thus, both lattice N and N2 reduction mechanisms involve oxide-supported V surface sites ([V]O) in preference to N-supported sites ([V]N). DFT calculations revealed the formation of V≡N:, V-N=N-H, plus other plausible reaction intermediates that are energetically favored at [V]O rather than at [V]N surface sites. Acknowledgment: This work was supported by the National Science Foundation through grants DMR-2112864 (to JAK, TRC, and FD) and partial support by CHE-1953547 (to TRC). Additional NSF support for the UNT CASCaM HPC cluster via Grant CHE-1531468 is also gratefully acknowledged. Ganesan, A. Osonkie, P. Chukwunenye, T. Cundari, F. D'Souza, J. Kelber. Electrochemical Reduction of N2 to ammonia by vanadium oxide thin films at neutral pH, J. Electrochem. Soc., 2021, 168, 026504.Osonkie, A. Ganesan, P. Chukwunenye, F. Anwar, K. Balogun, M. Gharee, I. Rashed, T. R. Cundari, F. D’Souza, and J. A. Kelber, Electro-catalytic reduction of nitrogen to ammonia: The roles of lattice O and N in reduction at vanadium oxynitride surfaces, ACS Adv. Mater & Interface, 2021, in revision.

Vanadium trioxide mediated peroxymonosulfate for fast metronidazole oxidation: Stepwise oxidation of vanadium for donating electrons

In this study, vanadium trioxide (V2O3) was adopted to activate PMS via a Fenton-like reaction to degrade metronidazole (MNZ). The V2O3-PMS system can almost completely degrade MNZ at 30 min with 42.4% TOC removal. Comparative tests reveal that V2O3 stands out among a variety of heterogeneous catalysts, including metallic oxides and carbon materials. Sulfate radicals (SO4•−) and hydroxyl radicals (•OH) derived from PMS decomposition are major reactive oxygen species, based on quenching tests, electron spin resonance (ESR) analysis, the steady-state concentrations of radicals ([SO4•−]ss = 5.1 × 10-13 M and [•OH]ss = 4.0 × 10-14 M), and kinetics model. The process of stepwise electron transfer from vanadium species to PMS to produce reactive radicals was proved by small-molecule simulation experiments and pickling experiments of vanadium oxides. Possible pathways of MNZ degradation were proposed based on the results of LC-MS and Fukui function, including two stages of the hydroxylation and bond cleavage of nitro and the subsequent ring-opening. This study reveals the high reusability and practicability of the V2O3-PMS system over a relatively wide pH range, which puts forward a new vision on V2O3 induced Fenton-like reactions and a new reference method for the removal of medical organic contaminants in water.

Vanadium recovery from Na2SO4-added V-Ti magnetite concentrate via grate-kiln process

Pilot experiments on Na2SO4-roasting of V-Ti magnetite (VTM) concentrate pellets were performed to activate vanadium with simulated grate-kiln machines. Combined with thermodynamic calculation, X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and inductively coupled plasma-atomic emission spectrometry (ICP-AES) analyses, process parameters of pellet making were optimized, and the enhancement of vanadium oxidation and conversion was realized. The results show that, in balling stage, adding Na2SO4 can promote the thermal decrepitation resistance of green pellets; in the drying stage, higher wind temperature can improve the dispersion of sodium salt in pellets; in preheating stage, using O2-rich hot gas can promote more thorough oxidation of vanadium; in roasting stage, the effect of vanadium conversion to sodium vanadate is better when the liquid amount is 15.5%-22.5%. Based on the above measures, the vanadium conversion rate achieved in the roasted pellets is 85.6%, proving the feasibility of vanadium recovery using an existing pellet production line.

Multistage suspension roasting of refractory stone coal: Enhanced extraction based on decarburization and vanadium oxidation

An innovative multistage suspension roasting technology for vanadium leaching from stone coal is proposed. The results reveal that 53.13% of the carbon is removed during the first-stage of roasting. At the same time, the vanadium-bearing mica lattice is disrupted, and the release of hydroxyl groups and vanadium leads to the production of dehydrogenated mica. In the second-stage of roasting, the carbon is almost completely removed, and the structure of mica is further destroyed and partially converted to feldspar under high-temperature roasting. The results show that under optimal conditions, i.e., first-stage roasting temperature of 800 °C, roasting time of 20 min, gas flow rate of 400 mL·min−1, the oxygen concentration of 20% and second-stage roasting temperature of 700 °C, roasting time of 1 h, and oxygen concentration of 20%, the vanadium leaching rate increases from 20% using conventional technology to 51.42% by using the presented technology.

Work Function Describes the Electrocatalytic Activity of Graphite for Vanadium Oxidation

In many applications such as vanadium flow batteries, graphite acts as an electrocatalyst and its surface structure therefore determines the efficiency of energy conversion. Due to the heterogeneity of the material, activity descriptors cannot always be evaluated with certainty because the introduction of defects is accompanied by a change in surface chemistry. Moreover, surface defects occur in multiple dimensions, and their occurrence and influence on catalysis must be separated. In this work, we have studied the surface of graphite felt electrodes by different methods in terms of morphology and chemistry to understand the electrocatalytic activity. We then defined the interaction between the surface and the electronic structure with particular emphasis on the work function and valence band. Using model catalysts with different architectures, we established correlations between the electrocatalytic activity and the size of the conjugation and the orientation of the edges. Finally, it was possible to link the level of the work function to the electrocatalytic activity.