High Vanadium Research Articles

Sub-20 nm ultrathin perfluorosulfonic acid-grafted graphene oxide composite membranes for vanadium redox flow batteries

Perfluorosulfonic acid (PFSA) membranes, such as Nafion, are widely used in vanadium redox flow batteries (VRFBs) because of their high proton conduction through the ion channels and excellent chemical stability. However, the high vanadium permeability of PFSA membranes induced by the randomly interconnected channels limits efficient cell operation. In this work, we demonstrate a sub-20 nm ultrathin PFSA-grafted graphene oxide/PFSA (PFSA-g-GO/PFSA) composite membrane with highly aligned ion channel morphology, which results in a 100-fold improvement in proton/vanadium ion selectivity compared to 25 μm-thick Nafion 211. In addition, the PFSA-g-GO nanosheets physically reinforce the ultrathin membrane while enabling the proton transport through the grafted PFSA ionomers, leading to stable cell operation at overall current densities from 40 to 200 mA cm−2. Especially, at a high current density of 200 mA cm−2, the PFSA-g-GO/PFSA composite membrane shows an energy efficiency (EE) of 78%, which is higher than that of Nafion 211, indicating its potential as an ion-selective membrane for VRFB.

The Role of Proton in High Power Density Vanadium Redox Flow Batteries.

To design high-performance vanadium redox flow batteries (VRFBs), the influence of proton on electrocatalysts cannot be neglected considering the abundance of proton in a highly acidic electrolyte. Herein, the impact of proton on metal oxide-based electrocatalysts in VRFBs is investigated, and a proton-incorporating strategy is introduced for high power density VRFBs, in addition to unraveling the catalytic mechanism. This study discloses that the metal oxide-based electrocatalyst (WO3) undergoes in situ surface reconstruction by forming H0.5WO3 after incorporating proton. Experimental and theoretical results precisely disclose the catalytic active sites. The battery with H0.5WO3 designed by a proton-incorporating strategy achieves an attractive power density of 1.12 W cm-2 and sustains more than 900 cycles without an obvious decay, verifying the outstanding electrochemical performance of H0.5WO3. This work not only sheds light on the influence of proton on electrocatalysts for rational design of advanced VRFBs catalysts but also provides guidelines for the fundamental understanding of the reaction mechanism, which is highly important for the application of VRFBs.

Simultaneous elimination of vanadium(V) and sulfamethoxazole from livestock wastewater with nitrogen-impregnated biochar

A cross-linked chitosan-modified birch sawdust biochar (CS@BSBC) was prepared and applied for the simultaneous elimination of vanadium (Ⅴ) and sulfamethoxazole (SMX) from livestock wastewater. The adsorption capacity of V(V) reached 110 mg/g alone while this value was promoted to 150 mg/g for the simultaneous removal of SMX and V(V), and the adsorption effect is optimal at pH 3. The adsorption capacity of SMX reached about 30 mg/g alone, while the SMX’s adsorption capacity droped to 25 mg/g for the simultaneous removal of SMX and V(V). The mechanism studies disclosed that redox reactions occur on the surface of CS@BSBC. As revealed by the XPS spectra, 63 % of V(V) was reduced to V(IV) concurrently pyrolic nitrogen and C−O terminals were oxidized to nitrogen oxide and CO. The treatment mechanism of CS@BSBC described above can provide a reference for the subsequent treatment of livestock wastewater with complex composition and high vanadium content.

Two-Dimensional MFI-Type Zeolite Flow Battery Membranes.

Vanadium flow battery (VFB) is one of the most reliable stationary electrochemical energy-storage technologies, and a membrane with high vanadium resistance and proton conductivity is essential for manufacturing high-performance VFBs. In this study, a two-dimensional (2D) MFI-type zeolite membrane was fabricated from zeolite nanosheet modules, which displayed excellent vanadium resistance (0.07 mmol L-1 h-1 ) and proton conductivity (0.16 S cm-1 ), yielding a coulombic efficiency of 93.9 %, a voltage efficiency of 87.6 %, and an energy efficiency of 82.3 % at 40 mA cm-2 . The self-discharge period of a VFB equipped with 2D MFI-type zeolite membrane increased up to 116.2 h, which was significantly longer than that of the commercial perfluorinated sulfonate membrane (45.9 h). Furthermore, the corresponding battery performance remained stable over 1000 cycles (>1500 h) at 80 mA cm-2 . These findings demonstrate that 2D MFI-type membranes are promising ion-conductive membranes applicable for stationary electrochemical energy-storage devices.

Two‐Dimensional MFI‐Type Zeolite Flow Battery Membranes

AbstractVanadium flow battery (VFB) is one of the most reliable stationary electrochemical energy‐storage technologies, and a membrane with high vanadium resistance and proton conductivity is essential for manufacturing high‐performance VFBs. In this study, a two‐dimensional (2D) MFI‐type zeolite membrane was fabricated from zeolite nanosheet modules, which displayed excellent vanadium resistance (0.07 mmol L−1 h−1) and proton conductivity (0.16 S cm−1), yielding a coulombic efficiency of 93.9 %, a voltage efficiency of 87.6 %, and an energy efficiency of 82.3 % at 40 mA cm−2. The self‐discharge period of a VFB equipped with 2D MFI‐type zeolite membrane increased up to 116.2 h, which was significantly longer than that of the commercial perfluorinated sulfonate membrane (45.9 h). Furthermore, the corresponding battery performance remained stable over 1000 cycles (>1500 h) at 80 mA cm−2. These findings demonstrate that 2D MFI‐type membranes are promising ion‐conductive membranes applicable for stationary electrochemical energy‐storage devices.

Copper-doped layered Fe2VO4 nanorods for aqueous zinc-ion batteries

Zinc-ion batteries (ZIBs) have attracted an increasing attention as a potential low-cost, environmentally friendliness, and high-safety energy storage system. Among them, transition metal vanadates with high oxidation state vanadium have great potential in ZIBs cathode research due to their high theoretical capacity. However, many vanadate particles still inevitably suffer from low ion mobility, low electrical conductivity and stability. Cation doping or compositing is an effective pathway capable of enhancing electrical conductivity. In this work, layered Cu-Fe2VO4 porous nanorods are obtained by introducing Cu2+ into MIL-88A(Fe) (a metal–organic framework; MIL stands for materials from Institute Lavoisier) and further ion-exchanged with NH4VO3, exhibiting excellent zinc storage properties as an cathode. The existence of oxygen vacancies and the change of electronic structure caused by Cu2+ substituting part of Fe2+ enhanced the conductivity and electron transfer rate. It delivers a reversible discharge capacity of 237 mAh/g at 0.3 A/g and a satisfactory high rate capacity of 126 mAh/g after 30 cycles at 5 A/g, and stable cycling performance (198 mAh/g after 1000 cycles at 1 A/g). Furthermore, the energy density can reached to 230.97 Wh kg−1 at 208.6 W kg−1. The assembled quasi-solid-state ZIBs maintain a high capacitance retention of 75% after 8000 cycles at 1 A/g.

Effect of vibration and cutting zone temperature on surface topography during hybrid cooling/lubrication assisted machining of Vanadis 10

Abstract New alloy materials developed to meet the increasing technological needs of people come into our lives with some difficulties in terms of machinability. New cooling and lubrication techniques have been developed to facilitate the workability of such difficult-to-process materials and protect the world ecologically and the quality of the produced product. The workpiece used in this study, Vanadis 10 SuperClean, is a high vanadium alloyed powder metallurgy tool steel offering a unique combination of excellent abrasive wear resistance in combination with a good chipping resistance. The present study investigated the effects of dry, cryo, and CryoMQL cutting conditions on cutting tool vibration amplitude, cutting temperature, surface roughness, tool wear, and tool life in turning of Vanadis 10 tool steel used in the automotive industry. The experiments were performed using TiCN/Al2O3/TiN coated cemented carbide tools and cutting parameters as the constant depth of cut (1 mm), feed rates (0.08, 0.1, 0.12 mm rev−1), and cutting speeds (80, 100, 120 m min−1). The results obtained from experiments showed that spraying liquid nitrogen into the cutting zone provided significant improvements on cutting temperature, tool wear, cutting tool vibration amplitude, and surface roughness. The best results in terms of all output were achieved in the CryoMQL cutting environment. CryoMQL environment has reduced surface roughness up to 65.03 %, flank wear 56.99 %, cutting temperature 32.77 %, and cutting tool vibration amplitude up to 42.76 % compared to dry machining.

Imidazole and imidazolium functionalized poly(vinyl chloride) blended polymer membranes reinforced by PTFE for vanadium redox flow batteries

A novel blended polymer membrane is prepared by a facile route for using as the diaphragm in vanadium redox flow batteries (VRFBs). The polymers polyvinylchloride (PVC) and polyvinylpyrrolidone (PVP) are first blended in a 1.2:1 mol ratio to give a PVP-PVC mixture, and the PVC in the mixture is then functionalized with 1-(3-aminopropyl)-imidazole (APIm). The functionalized polymers are impregnated into the porous polytetrafluoroethylene (PTFE) to fabricate membranes. The obtained membranes possess superior affinity to sulfuric acid mainly due to acid-base interactions between APIm groups and sulfuric acid molecules. The presence of hydrophobic PTFE restricts the deterioration of mechanical strength of membranes by doped acids. Moreover, the prepared membranes exhibit high oxidation stability and low vanadium permeability. The VRFB assembled with the proposed diaphragm displays energy efficiency above 82 % at a current density range of 20 to 120 mA cm−2. The membrane-based VRFB demonstrates stable performance after over 50 charge–discharge cycles.

Effect of Heat Treatment on Microstructure and Properties of Quenched and Tempered Steel with High Vanadium Contents

After heat treatment, the microstructure of quenched and tempered (Q&T) steel with high vanadium (V) content was characterized using metallographic and scanning electron microscopes (SEM). The proto-austenite grains of the tested steel were compared at different quenching temperatures, and the precipitation behavior of precipitates and matrix microstructure characteristics at various tempering temperatures were studied. Tensile properties and low-temperature impact toughness of the tested steel with different heat treatments were measured using an electronic universal testing machine and an impact testing machine. The findings indicate that as the quenching temperature increases, the size of the proto-austenite grains gradually increases. When the quenching temperature surpasses 920 °C, the size of the proto-austenite grains obviously increases. With a constant tempering temperature, an increase in quenching temperature results in a decrease in the size of precipitates. With a constant quenching temperature, an increase in tempering temperature results in an increase in the size of precipitates. Therefore, the tested steel quenched at 920 °C for 1 hour and then tempered at 630 °C for 1.5 hours would obtain excellent comprehensive mechanical properties, with a tensile strength of 1233 MPa and a low-temperature impact value of 64 J.

Effect of V2O5 on Consolidation, Reduction, and Softening-Melting Behavior of High-Cr Vanadium Titanomagnetite

Vanadium titanomagnetite is an important mineral resource. It is a raw material for ironmaking, vanadium extraction, strategic metal titanium production, and titanium dioxide production. In this study, high chromium vanadium titanomagnetite (High-Cr VTM) and ordinary iron ore were used as raw materials for pelletizing. The effect of V2O5 on the preparation and properties of High-Cr VTM pellets was studied. The influence of V2O5 on the properties of the green pellets, the compressive strength of oxidized pellets, the reduction swelling index and reduction degree, softening-melting behavior, and the migration law of Fe, Ti, and Cr in the reduction process were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that with the increase in V2O5 content, the properties of the green pellets basically showed a trend of first decreasing and then increasing but all met the basic requirements of pelletizing. When the added amount of V2O5 in the pellet was 6%, the compressive strength of the oxidized pellet was the lowest at only 2565 N/pellet but it still met the quality requirements for pellets in blast furnace production. As the dosage of V2O5 increased, the reduction swelling index and reduction degree of the pellets showed a trend of first increasing and then decreasing. The addition of V2O5 can increase the softening initial temperature, softening final temperature, melting start temperature, and dripping temperature of the High-Cr VTM pellets, narrowing the softening interval, and expanding the melting dripping interval. The experimental results provided a data reference for revealing the influence of V2O5 on High-Cr VTM pellets during the blast furnace smelting process.

Vanadium–Titanium Magnetite Concentrate, Calcium–Magnesium Composite Roasting and Sulfuric Acid Leaching for Vanadium Extraction from Pellets

This paper investigated a pellet ore production process in which vanadium was extracted from vanadium and titanium magnetite concentrates using sulfuric acid leaching. Calcium and magnesium were added to the iron ore concentrate during pellet production to produce calcium vanadate and magnesium vanadate after roasting. The pellets were leached with sulfuric acid solution to extract V5+. The resulting pellets had a compressive strength of 3375 N after primary roasting, a good pellet morphology after acid leaching, and simple liquid–solid separation. Under the optimal experimental conditions, the vanadium leaching rate in the pellets reached 77.86%, while the iron leaching rate was only 1.17%. The pellets did not fragment, which was an improvement upon existing vanadium extraction methods. The strength of the pellets after vanadium extraction decreased to 563 N, but after secondary roasting, the compressive strength of the pellets reached 2578 N, which was suitable for blast furnace ironmaking. The roasting and acid leaching experiments showed that the vanadium extraction process resulted in suitable pellet properties. The use of low compound additives can effectively improve the leaching effect, while avoiding the previous problems of too many additives, pellet iron grade reduction, or the pursuit of high vanadium extraction rate pellet breakage and serious high secondary use process costs.

Enhanced electrochemical performance of MnO2 by high oxidation state vanadium(Ⅴ) doping

Due to the poor conductivity, α-MnO2 exhibits a low specific capacity and bad rate performance, meantime, the repeated insertion/extraction of Zn2+ in MnO2 results in the collapse of its tunnel structure, leading to the rapid decay of cyclic performance, which seriously affects the practical application of aqueous Zn-MnO2 batteries. Studies have shown that doping is an effective method to improve the electrochemical properties of MnO2. As we have learned, the current studies mainly adopt low oxidation state cations (such as Ni2+, Co2+, Zn2+,Ca2+, K+ and Al3+). Herein, high oxidation state Vanadium(Ⅴ) was used for doping, the resulted Manganese and Oxygen vacancies enhanced the diffusion of Zn2+ and improved the reversibility and rate performance of MnO2. When cycled at 3 C (1 C = 308 mA g−1), the specific capacity of V-MnO2(0.06) kept stable at 300 mAh g−1 and there was no indication of any evidence of decay, even if proceeded 400 cycles. High-oxidation-state Vanadium(Ⅴ) doping and resulted vacancy defects synergistically improved the electrochemical properties of MnO2, providing new ideas for MnO2 modification.

Reactive crystallization of ammonium polyvanadate from vanadium-bearing solution assisted by efficient ultrasound irradiation: Crystallization characteristics and growth process

Ultrasound crystallization (UC) technique was previously proposed to solve the issues caused by the acidic ammonium salts crystallization of vanadium. In this work, the influence of various parameters on vanadium crystallization characteristics were detailedly investigated. Results showed that high vanadium precipitation ratio (99.67%) and V2O5 purity (99.50%) of the final products can be obtained under the conditions of ultrasonic power of 600 W, initial pH value of 2.0, reaction temperature of 95 °C, ammonium salt addition coefficient of 0.5, reaction duration of 5 min and vanadium concentration of 20 g/L. Moreover, the NH4+ content in the supernatant liquid was notably reduced to 1.08 g/L. Crystallization kinetic analysis manifests that the crystallization rate constant augments with the increasing temperature, and the activation energy and pre-exponential factor is 71.87 kJ/mol and 7.44 × 109, respectively. Ultrasound enhances the collision frequency between NH4+ and vanadium ions, further improving the crystallization rate of the (NH4)2V6O16 crystals. Meanwhile, ultrasound induces a secondary nucleation, which would promote the intercalation among small flakes and further improves the nucleation and growth of the (NH4)2V6O16 crystals. Scanning electron microscopy analysis demonstrates that the flaky crystals are firstly formed, then a part of flakes gradually intercalate with each other, and finally most of the lamellar crystals complete the intercalation process. Meanwhile, selected area electron diffraction verifies the single crystalline characteristic of the micron-flakes, which grows along the (010) crystal plane. This work will lay theoretical and technical basis for UC technique appliance and promote the progress of the vanadium extraction industry.

Nano TiC electrocatalysts embedded graphite felt for high rate and stable vanadium redox flow batteries

Developing electrodes with high stability and activity is critical to promoting the application of redox flow batteries. In this work, a multiscale-pore-network structured graphite felt embedded nano-sized TiC electrocatalysts is fabricated by fully utilizing the Ti and O atoms of TiO2 nano seeds. For the present electrode, the micro pores shaped by the crossed carbon fibers serve as pathways for electrolyte convection. At the same time, the simultaneous formation of TiC during nanopore fabrication can catalyze the V3+/V2+ redox reaction. The electrode leads to the battery performance with an energy efficiency of 85.2% and an electrolyte utilization of 82.7% at a current density of 200 mA cm−2, respectively 23.3% and 48.6% higher than the battery with pristine electrodes. Also, even at 300 mA cm−2, the battery's energy efficiency and electrolyte utilization with this electrode can still be maintained at 80.8% and 72.6%, respectively 14.0% and 29.6% higher than the thermally treated electrode. Moreover, the present battery demonstrates a stable energy efficiency above 80% during cycle tests. The results indicate that engineering structures of electrocatalysts in nanopores may open new avenues for advancing flow battery electrode technology.

Effect of oxygen enrichment on sintering behavior of high proportion vanadium–titanium magnesite concentrates

Effect of oxygen enrichment on sintering behavior of high proportion vanadium–titanium magnesite concentrates

Anion Exchange Membranes Based on Bis-Imidazolium and Imidazolium-Functionalized Poly(phenylene oxide) for Vanadium Redox Flow Battery Applications.

Although the Nafion membrane has a high energy efficiency, long service life, and operational flexibility when applied for vanadium redox flow battery (VRFB) applications, its applications are limited due to its high vanadium permeability. In this study, anion exchange membranes (AEMs) based on poly(phenylene oxide) (PPO) with imidazolium and bis-imidazolium cations were prepared and used in VRFBs. PPO with long-pendant alkyl-side-chain bis-imidazolium cations (BImPPO) exhibits higher conductivity than the imidazolium-functionalized PPO with short chains (ImPPO). ImPPO and BImPPO have a lower vanadium permeability (3.2 × 10-9 and 2.9 × 10-9 cm2 s-1) than Nafion 212 (8.8 × 10-9 cm2 s-1) because the imidazolium cations are susceptible to the Donnan effect. Furthermore, under the current density of 140 mA cm-2, the VRFBs assembled with ImPPO- and BImPPO-based AEMs exhibited a Coulombic efficiency of 98.5% and 99.8%, respectively, both of which were higher than that of the Nafion212 membrane (95.8%). Bis-imidazolium cations with long-pendant alkyl side chains contribute to hydrophilic/hydrophobic phase separation in the membranes, thus improving the conductivity of membranes and the performance of VRFBs. The VRFB assembled with BImPPO exhibited a higher voltage efficiency (83.5%) at 140 mA cm-2 than that of ImPPO (77.2%). These results of the present study suggest that the BImPPO membranes are suitable for VRFB applications.

Development of Fe-containing BCC hydrogen storage alloys with high vanadium concentration

Vanadium-based alloys are promising hydrogen storage materials which reversibly absorb hydrogen > 2.0 wt% under ambient conditions. In present study, we systematically investigated the V-Ti-Cr-Fe quaternary alloys with V concentration of 65–80 at% and discussed the relationship between hydrogen sorption properties and lattice parameter (a) and valence electron density (e/a). When 3.023 ≤ a ≤ 3.031 Å and e/a ≤ 5.12, the alloys show the hydrogen desorption amount ≥ 2.30 wt% and desorption plateau pressure ≥ 0.1 MPa at 298 K. More interestingly, compared to the Fe-free V75-Ti-Cr (Ti/Cr = 0.9) alloy, addition of 1–3 at% Fe could improve the hydrogen desorption amount and plateau pressure. The optimized alloy, V75-Ti-Cr-Fe2 (Ti/Cr = 0.9), shows a reversible hydrogen capacity of 2.46 wt% at 298 K in the 1st cycle and the capacity retention rate of 96 % after 100 cycles.

Aspergillus Niger Derived Wrinkle-Like Carbon as Superior Electrode for Advanced Vanadium Redox Flow Batteries.

The scarcity of high electrocatalysis composite electrode materials has long been suppressing the redox reaction of V(II)/V(III) and V(IV)/V(V) couples in high performance vanadium redox flow batteries (VRFBs). Herein, through ingeniously regulating the growth of Aspergillus Niger, a wrinkle-like carbon (WLC) material that possesses edge-rich carbon, abundant heteroatoms, and nature wrinkle-like structure is obtained, which is subsequently successfully introduced and uniform dispersed on the surface of carbon fiber of graphite felt (GF). This composite electrode presents a lower overpotential and higher charge transfer ability, as the codoped multiheteroatoms increase the electrocatalysis activity and the wrinkled structure affords more abundant reaction area for vanadium ions in the electrolyte when compared with the pristine GF electrode, which is also supported by the density functional theory (DFT) calculations. Hence, the assembled battery using WLC electrodes achieves a high energy efficiency of 74.5% for 300 cycles at a high current density of 200mA cm-2 , as well as the highest current density of 450mA cm-2 . The WLC material not only uncovers huge potential in promoting the application of VRFBs, but also offers referential solution to synthesis microorganism-based high-performance electrode in other energy storage systems.

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.

Fabrication and abrasive wear property of high chromium cast iron with high vanadium and high nitrogen content (HCCI-VN)

High chromium cast irons (HCCIs) have excellent wear resistance because of high hardness chromium carbides (M7C3). However, the hardness of M7C3 is relatively low compared with MC-type carbides, such as VC, NbC and TiC. To improve wear resistance of HCCI, a new HCCI, named HCCI-VN, was fabricated by replacing wt.5.0% chromium with 5.0 wt% vanadium and adding 0.1 wt% nitrogen in traditional HCCI with 20 wt% Cr, and the abrasive wear properties of HCCI-VN were researched under different abrasive size and load conditions. Results show that the microstructure of HCCI-VN was characterized by many V(C, N) carbides besides chromium and molybdenum carbides (M7C3, M23C6, M2C), which were distributed in the matrix composed of martensite and austenite. The new HCCI-VN has excellent wear resistance. The relative wear resistance HCCI-VN is 2.2–9.1 times that of HCCI with 23 wt% Cr under different abrasive size and wear load. Among them, the reduction of abrasive size or the increase of wear load will bring better wear resistance. The excellent wear resistance of HCCI-VN is attributed to high hardness V(C, N), which cooperates with multi-scale and multi-type chromium and molybdenum carbides to resist abrasive scratch efficiently.