Vanadium Oxidation Research Articles

Flexible Vanadium Dioxide Films and Devices on Kapton Fabricated With Low-Temperature Atmospheric Oxidation of Vanadium

Flexible Vanadium Dioxide Films and Devices on Kapton Fabricated With Low-Temperature Atmospheric Oxidation of Vanadium

Robust ferromagnetic V0.05-XCoxZn0.95O (x = 0.01, 0.02, 0.03, 0.04, 0.05) nano-compounds: New dilute magnetic-semiconductors with tailored optical activity

The development of diluted magnetic semiconductors (DMS) that combine magnetic properties with semiconducting behavior is a promising area of research that could lead to the creation of entirely new types of devices that are faster, more efficient, and potentially cheaper. In this investigation, DMS nanocompositions represented by V0.05-XCoxZn0.95O, (x = 0.01, 0.02, 0.03, 0.04, 0.05) were synthesized via a modified Pechini-sol-gel process. X-ray analysis showed a successful incorporation of V and Co ions into ZnO structure. The size and shape of the nanoparticles changed depending on the V/Co doping percentage. The addition of the blend of 2 wt% V and 3 wt% Co ions significantly reduced the particle size from 21 nm to 14 nm. The X-ray photoelectron analysis identified complex interactions between vanadium/cobalt dopants and the surrounding ZnO lattice with significant influence of cobalt incorporation on vanadium's oxidation state. It further revealed a significant influence of cobalt incorporation on vanadium’s oxidation state. Vanadium primarily exists as V3+ upon vanadium-mono doping (ZV5). However, co-doping with Co/V leads to a shift towards the V5+ state. Enhanced absorption extending into the visible light region was observed in either mono or (V/Co) co-doped samples. Notably, the band gap energy decline was more pronounced in the 5 mol% Co-doped ZnO, recording a value of 2.58 eV. An additional band gap around 1.8 eV appeared in Co-doped samples, potentially due to transitions in Co2+ ions. The combination of V and Co induced a ferromagnetic behavior with fully saturated order. The ZV3C2 composition exhibits the most promising characteristics, boasting the highest saturation magnetization (1.037 emu/g). Accordingly, robust ferromagnetism of V0.05-XCoxZn0.95O, (x = 0.01, 0.02, 0.03, 0.04, 0.05) nano-particles is a promising approach for spintronic applications.

Mechanism and kinetics study of vanadium leaching from landfilled metallurgical residues by ultrasonic with ozonation enhancement in a low-acid medium

Landfilled metallurgical residues are valuable raw materials for the recovery of strategic vanadium resources. However, efficient separation of vanadium from these residues is challenging due to its strong oxidation resistance and coating within silicate inclusions. To address this issue, this study proposes an enhanced leaching process utilizing the synergistic effect of O3-catalyzed ultrasonic field in a low concentration sulfuric acid system. Results show that following a 10-minute O3 and ultrasonic treatment, the direct leaching rate of vanadium experienced a remarkable 46.7 % increase. Quenching experiments revealed a hierarchical order of active species within the reaction process:⋅OH >⋅O2−> H+, with⋅OH oxidation exhibiting the most pronounced capacity for disrupting the inclusion structure. Electron Paramagnetic Resonance analysis indicated that the highest⋅OH yield arose from the combined application of ultrasound and ozone. Kinetic investigations demonstrated that the vanadium leaching process is governed by interfacial chemical reactions. The activation energy of vanadium oxidation leaching under ultrasonic-O3 conditions was determined to be 40.41 kJ/mol, representing a 20.19 % reduction compared to ultrasonic conditions alone. Through the integration of analysis, characterization, and comparative evaluations, it was discerned that the synergistic impact of ultrasonic and ozone treatments significantly enhances the breakdown of silicate inclusions by low-concentration HF, particularly in the conversion of SiOSi bonds into SiOH bonds and SiF bonds. In summary, the refined leaching methodology incorporating ozone catalysis in conjunction with ultrasonic treatment provides a new idea for the separation and extraction of refractory residual vanadium.

Extraction of Vanadium from CaO–SiO2–MgO–Al2O3 Slags Based on Vaporization of Vanadium Pentoxide

Vanadium is an important micro‐alloying element for various steel grades. Consequently, it is also present in the slags used in the production of those grades. During steelmaking, the vanadium vaporization from the slag is not desirable, as it increases vanadium consumption and at the same time releases toxic vapors of its higher oxides. However, the recovery of vanadium from the slag after the processing is worthwhile. In oxidic form as vanadium pentoxide (V2O5), vanadium can be extracted from the slag. In this research, the vaporization behavior of vanadium from CaO–SiO2–MgO–Al2O3 industrial slag is investigated at 1873 K. The effect of different process parameters, e.g., the pressure in the furnace chamber, the duration of the oxygen treatment of the slag, and the oxygen flow rate, is considered. The effect of P2O5 and Fe2O3 addition on the extraction of vanadium is studied. It is possible to induce formation of V2O5 gas bubbles in the slag due to the oxidation of vanadium. Thus, vanadium respectively V2O5 is extracted from the slag.

Probing Carbon Materials Towards the Vanadium(IV)/(V) Reaction by Scanning Electrochemical Microscopy

AbstractA method is presented to quantitatively analyze the reduction of vanadium(V) to vanadium(IV) over two flat carbon substrates (glassy carbon and graphite foil) using the feedback mode of scanning electrochemical microscopy. A pulse profile is validated and applied during approach curve experiments of a 10 μm Pt microelectrode. By fitting the approach curve data, electron transfer constants are calculated for various potentials and k0 is extracted from the corresponding Tafel plot. Furthermore, surface functional groups were introduced to the carbon substrates by acid treatment; however, kinetic parameters of the sluggish reduction reaction were only influenced to a minor extent. Finally, the same approach, combined with in situ‐Raman microscopy, is applied to a single graphene layer using a 2.7 μm Pt microelectrode. In this case, increased activity for both, the vanadium(V) reduction and vanadium(IV) oxidation reaction, was found close to the graphene edge sites by means of electrochemical microscopy for the first time.

Highly Exothermic and Fast Mechanochemical Redox and Intercalation Reactions of V2O5 with Sodium Hydride.

Vanadium oxides exhibit promising characteristics for electrochemical energy storage, owing to their capability to switch between different oxidation states, in combination with the incorporation of alkali metals. Here, we report on a systematic investigation of the mechanochemical reduction of V2O5 with NaH. In contrast to conventional high-temperature synthesis methods, the mechanochemical reaction occurs already after a few minutes. We observed a mixture of different (sodium) vanadium oxides with vanadium oxidation states ranging from +III to +V. Remarkably, these highly exothermic self-propagating reactions occur even within a rudimentary pistil-mortar setup. Hereby, the hydride concentration has a greater effect on the final sample composition than the milling time. In general, higher percentages of sodium vanadates are formed instead of vanadium oxides, and the lower oxidation states of vanadium are accessible with increasing amounts of NaH. Theoretical calculations confirm these experimental observations and emphasize the central role of sodium vanadates, especially with vanadium in the +V oxidation state, in carrying out the observed exothermic reactions. This comprehensive study sheds light on the mechanochemical reduction of vanadium oxides and underlines their potential for further development of electrochemical energy storage systems.

Self-charging V2CTx/CNT-based zinc ion micro-supercapacitor for wearable electronics

The flexible self-charging zinc ion micro-supercapacitors (ZIMSC) that can be effectively charged by harvesting ubiquitous energy from the air, not only achieve power supply anytime and anywhere but also improve the integrated degree without external charging plug or cable, enabling it a promising candidate for the wearable electronic device in various environmental scenarios. Herein, we reported a chemically self-charging ZIMSC based on a free-standing V2CTx/CNT electrode. Introducing 1D CNT into 2D V2CTx fundamentally overcomes the self-stacking problem of the nanosheets while providing additional ion transport paths and improving the conductivity of active electrodes. The area-specific capacity of V2CTx/CNT-based ZIMSC achieves 117.2 mF cm−2 after 8.0 h self-charging. The excellent self-charging performance is attributed to the oxidation of vanadium in the V2CTx-based cathode stimulated by ambient oxygen, accompanied by the Zn2+ deintercalation process. The flexible ZIMSC exhibited an optimal area capacitance of 246.88 mF cm−2 at a current density of 0.5 mA cm−2. Additionally, the self-charging ZIMSC is integrated with the V2CTx-based pressure sensors for a self-powering wearable system that exhibits excellent stability over 50,000 loading/unloading cycles. This work provides a rational design for constructing highly efficient self-charging energy storage devices and broadens the horizons of flexible wearable devices.

Boosting the capacity and stability of Na3V2(PO4)2F3-2xO2x microspheres, using atomic layer deposition of artificial CEI

Phosphate-based materials [e.g. Na3V2(PO4)2F3-2xO2x; (NVPFO2x;0 < x < 1)] are regarded as a promising intercalation cathodes for Sodium-ion batteries (SIBs) due to their high reversible specific capacity and stability. However, so far only 2 Na ion were demonstrated to be active in these polyanionic cathodes, which limit their capacity. Herein we provide a strategic approach towards electrochemical activation of a 3rd Na ion, which leads to higher capacity, and preserves structural integrity. We synthesize and study a series of NVPFO2x (0 < x < 1) with well-controlled surface morphology and vanadium oxidation state, and study the dependence of the electrochemical behavior on the various composition and morphology. The optimized NVPFO cathode exhibited highest initial specific discharge capacity (131 mA h g−1) indicating the activation of 3rd Na ion. Nevertheless, the material suffers rapid capacity fading within ~50 cycles. We demonstrate how this instability is suppressed profoundly through the formation of a thin artificial cathode electrolyte interface (CEI) layer of TiO2 (ca. 2 nm) on the surface of NVPFO by atomic layer deposition (ALD). This TiO2 coating enabled even further extraction of sodium through higher voltage domain, but more importantly, it facilitated excellent long-term stability over 200 cycles. The structural stability of the cathode material was revealed by post cycling HRSEM, XPS, and XRD study. All these studies demonstrate that the thin TiO2 layer effectively contributes to formation of a robust CEI layer, diminishes the parasitic reaction on the electrode surface, reduces carbonate formation, and restricts the electrolyte decomposition.

Promoting the Calcified Roasting of Vanadium Slag Based on the CeO2-Catalytic Oxidation Mechanism.

Calcification roasting-acid leaching is a clean, efficient, and environmentally friendly process, but in the roasting process, the local temperature is often too high, the heat release is not timely, and the heat transfer is blocked. Furthermore, the material is easy to sinter, which affects the final vanadium extraction effect. In this paper, a small amount of CeO2 was introduced in the roasting process of vanadium slag to promote the calcified roasting. The results showed that the vanadium leaching rate reached 93.17% with the addition of 0.1 wt % CeO2 at a roasting temperature of 750 °C, which was higher than that obtained without CeO2 addition (90.00%). The results of XPS, XRD, and SEM-EDS analyses confirmed that adding CeO2 to the roasted clinker significantly increased the proportion of pentavalent vanadium to the total vanadium by up to 28.64%. O2-TPD analysis revealed an enhanced chemisorbed oxygen with the CeO2-assisted roasting, indicated the activation of oxygen by CeO2, and resulted in an enhanced oxidation of vanadium. The work in this paper establishes an alternative route for catalytic oxidation-enhanced vanadium slag roasting, which can improve the utilization of vanadium slag at relatively lower temperatures under the action of CeO2 and is of positive significance in solving the problems of sintering and energy consumption in the roasting process.

Designing a 3D framework NaVOPO4 as a high-power, low-strain and long-life positive electrode material for Na-ion batteries

Advances in sodium-ion batteries hugely rely on perfecting the performance of active electrode materials. In this paper, we offer a new NaVOPO4 polymorph adopting a KTiOPO4-type framework as a promising high-rate, low-strain and long-life positive electrode material for sodium-ion batteries. NaVOPO4 is prepared via a facile hydrothermally-assisted solid-state ion exchange. The crystal structure is refined based on synchrotron X-ray powder diffraction (XRD) and validated by X-ray absorption spectroscopy (XAS), transmission electron microscopy analysis and density functional theory (DFT) calculations. The electrochemical performance of NaVOPO4 is evaluated through galvanostatic charge/discharge tests, cyclic voltammetry, potentiostatic intermittent titration and electrochemical impedance spectroscopy. A carbon-coated NaVOPO4 demonstrates a specific capacity of ∼110 mAh g–1 at a C/10 rate at an average potential of ∼3.93 V vs. Na+/Na. The material exhibits decent capacity retention and rate capability, maintaining over 74 % of the initial capacity after 1000 cycles at a C/2 rate and around 87% at a 2C charge/discharge rate. Diffusion coefficients of 10–11 cm2 s–1 and DFT-calculated energy barriers of ∼0.15–0.35 eV indicate fast Na+ ion diffusion within the NaVOPO4 framework. The vanadium oxidation state and charge compensation mechanism in NaVOPO4 are studied by XAS and DFT. Moreover, the operando XRD analysis coupled with DFT elucidates several phase transitions occurring in NaVOPO4 with an exceptionally low volume variation of 2.4% in total, highlighting the reversibility and structural stability during Na+ de/insertion. Overall, NaVOPO4 exhibits attractive electrochemical performance and stability, making it a potential candidate for sodium-ion battery cathode materials.

Low‐Temperature Atomic Layer Deposition Synthesis of Vanadium Sulfide (Ultra)Thin Films for Nanotubular Supercapacitors

Herein, the synthesis of vanadium sulfide (VxSy) by atomic layer deposition (ALD) based on the use of tetrakis(dimethylamino) vanadium (IV) and hydrogen sulfide is presented for the first time. The (ultra)thin films VxSy are synthesized in a wide range of temperatures (100–225 °C) and extensively characterized by different methods. The chemical composition of the VxSy (ultra)thin films reveals different vanadium oxidation states and sulfur‐based species. Extensive X‐ray photoelectron spectroscopy analysis studies the effect of different ALD parameters on the VxSy chemical composition. Encouraged by the rich chemistry properties of vanadium‐based compounds and based on the variable valences of vanadium, the electrochemical properties of ALD VxSy (ultra)thin films as electrode material for supercapacitors are further explored. Thereby, nanotubular composites are fabricated by coating TiO2 nanotube layers (TNTs) with different numbers of VxSy ALD cycles at low temperature (100 °C). Long‐term cycling tests reveal a gradual decline of electrochemical performance due to the progressive VxSy thin films dissolution under the experimental conditions. Nevertheless, VxSy‐coated TNTs exhibit significantly superior capacitance properties as compared to the blank counterparts. The enhanced capacitance properties exhibited are derived from the presence of chemically stable and electrochemically active S‐based species on the TNTs surface.

The Synthesis of Sponge-like V2O5/CNT Hybrid Nanostructures Using Vertically Aligned CNTs as Templates.

The fabrication of sponge-like vanadium pentoxide (V2O5) nanostructures using vertically aligned carbon nanotubes (VACNTs) as a template is presented. The VACNTs were grown on silicon substrates by chemical vapor deposition using the Fe/Al bilayer catalyst approach. The V2O5 nanostructures were obtained from the thermal oxidation of metallic vanadium deposited on the VACNTs. Different oxidation temperatures and vanadium thicknesses were used to study the influence of these parameters on the stability of the carbon template and the formation of the V2O5 nanostructures. The morphology of the samples was analyzed by scanning electron microscopy, and the structural characterization was performed by Raman, energy-dispersive X-ray, and X-ray photoelectron spectroscopies. Due to the catalytic properties of V2O5 in the decomposition of carbonaceous materials, it was possible to obtain supported sponge-like structures based on V2O5/CNT composites, in which the CNTs exhibit an increase in their graphitization. The VACNTs can be removed or preserved by modulating the thermal oxidation process and the vanadium thickness.

Dynamic multi-color switching using ultrathin vanadium oxide on aluminum-based asymmetric Fabry–Pérot resonant structure

Vanadium dioxide (VO2) exhibits strong infrared optical switching due to its insulator–metal phase-transition property. However, in the visible wavelengths, its intrinsic optical switching is quite low. Current research explores solutions like multilayering, intricate structural patterning, high thermal budget processes, and costly metals for improved color switching. Nonetheless, the color gamut coverage with these methodologies remains notably limited. This work overcomes these limitations and demonstrates dynamic multi-color switching covering a large color gamut using a simple, unpatterned, ultrathin (∼ λ14, where wavelength λ is taken as 575 nm at the center of the visible spectrum) asymmetric Fabry–Pérot structure of VO2 on aluminum (Al). We use the transfer matrix method to design the VO2/aluminium (Al)/sapphire structure for maximum visible reflectance switching. VO2 films are synthesized using a simple, low thermal budget atmospheric oxidation of vanadium (V). With varying oxidation durations, different colors of the oxidized samples are observed. Consistent and reversible color-switching is observed visibly and in reflectance measurements with the change in temperature from low (RT ∼ 30 °C) to high (HT ∼ 100 °C) or vice versa due to the phase transition property of the VO2 layer in the structure. Compared to the existing studies, this work shows a significant change in chromaticities and covers a large color gamut when plotted on the CIE chromaticity diagram. This work has potential applications in the fields of display, thermochromic structures, and visible camouflage.

Employing a Thin Artificial CEI Layer on Na3V2 (PO4)2F3-2xO2x (0 < x < 1) by Atomic Layer Deposition; Structure Stabilization and Capacity Enhancement

Sodium ion battery (SIB), still facing the limit in functionality due to lower energy density; arises from either low capacity or narrow potential window. The capacity improvement within material sustainability is one major challenge which needs to be addressed to satisfy the present demand for SIB. Of late phosphate-based materials [Na3V2(PO4)2F3-2xO2x; (NVPFO2x;0 < x < 1)] are established as prospective cathodes for Sodium-ion battery (SIB) due to high reversible capacity and stability. However, the reversible extraction and insertion of only 2 Na ion per formula unit in these polyanionic cathodes limit their capacity. Herein we demonstrate a strategic approach towards electrochemical activation of 3rd Na ion which leads to higher capacity and preserves structural stability. We synthesized a series of NVPFO2x (0 < x < 1) with well-controlled surface morphology and vanadium oxidation state and studied the electrochemical behavior on the various composition and morphology. Cycling within the potential window of 1.2V to 4.3V vs Na/Na+ to trigger extra Na ion in the electrochemical activity have shown their explicit behavior depending on morphology. The optimized NVPFO2x shows specific capacity >130 mA h g-1, implies 3rd Na ion activation. However, the material suffers rapid capacity fading within ~ 65 cycles which is tremendously improved through formation of a thin artificial cathode electrolyte interface (CEI) layer of TiO2 on the surface of NVPFO2x by atomic layer deposition (ALD) technique. This TiO2 coating enabled even further extraction of sodium through higher voltage domain, but more importantly, it facilitated excellent long-term stability over 200 cycles. The thin coating explicitly restores the structural and morphological integrity during prolonged electrochemical cycling which established by post cycling XRD, HRSEM and XPS study. The study demonstrated that the thin TiO2 layer on electrode material is effectively diminishes the parasitic reaction, reduces carbonate formation, and increase the stability of the formed CEI and lowers electrolyte decomposition within wide-range potential window.

Selective Gamma-Ray Ionisation of Vanadium Oxides: Towards the Formation of VO2

In this study, we report on the valence control of vanadium oxidation states towards stabilising VO2 thin films. X-ray diffraction measurements indicate that up to 300 kGy of gamma-ray radiation the VO2 phase remains monoclinic, with the crystallite size only varying slightly with the dose. X-ray photoemission spectroscopy indicates the presence of three oxide phases (VO2, V2O3 and V2O5) on the samples. A decrease in the oxidation states of V3+ and V5+ and an increase in the valence state V4+ are observed for irradiations up to 300 kGy, which favours the vanadium dioxide VO2 formation.

Phase transformation and roasting kinetics of vanadium slag in air atmosphere

The essential supply of vanadium for production, vanadium slag, is generally extracted by way of roasting-leaching process. In roasting, it was located that the leaching charge of vanadium improved and the break of spinel is more obvious with the rise of roasting temperature. The phase transformation of vanadium slag happened in the roasting process, but it is unclear that the “kinetic triplet factors” of the activation of vanadium slag after roasting. Therefore, the apparent activation energy (E) and the pre-exponential factor (A) of olivine and spinel oxidation were obtained by FWO method and KAS method. The E value were 140.97 kJ/mol (olivine) and 214.68 kJ/mol (spinel). The pre-exponential factors were 446491.41 min−1 (olivine) and 420236191.33 min−1 (spinel). The chemical reaction control and 3-D diffusion Zhuraalev-Lesokin-Tempelman mechanism model were determined by Malek method. The results show that the activation energy of vanadium oxidation process can be increased by increasing the roasting temperature at 1100 K-1250 K, which makes the conversion of spinel phase difficult. From the perspective of kinetics, it is important to select a reasonable roasting temperature to improve the activation roasting efficiency of vanadium slag. This study provides some theoretical guidance for strengthening the roasting process and efficient extraction of V element of vanadium slag.

Li2O–V2O5–MoO3–Fe2O3 amorphous cathode material for lithium-ion batteries based on coordinated multi-electron effect and stable network structure

The amorphous cathode materials Li2O–V2O5–MoO3 and Li2O–V2O5–MoO3–Fe2O3 were produced via melt quenching. By analyzing the structure, elemental valence, and electrochemical characteristics of Li2O–V2O5–MoO3 at different ratios, the effects of MoO3 addition on vanadium-based amorphous cathode materials were explored. 20Li2O–60V2O5–20MoO3 has a high initial capacity (268.0 mAh/g for the first reversible discharge at a current density of 50 mA/g), which is based on the properties that MoO3 supplies additional oxidation reductions and has [MoO6] structural units to widen the diffusion channels for lithium ions in the network structure. Unfortunately, the network of the structural elements [MoO6] and [VO4] is unstable, which causes the material to have poor cycle stability and exhibit an unsatisfactory current response. The network structure stability of Li2O–V2O5–MoO3–Fe2O3 is increased by adding Fe2O3 to provide [FeO4], which strengthens the link between each structural unit. Vanadium oxidation reductions are promoted, and iron oxidation reductions replace the role of molybdenum in the charge/discharge. The discharge product transforms from LiVMoO5 to Li2FeV3O8 with increased de-embedding Li efficiency. The 20Li2O–60V2O5–10MoO3–10Fe2O3 achieves an initial reversible specific capacity of 255.2 mAh/g at 50 mA/g, 139.7 mAh/g additional specific capacity after 100 cycles, and 110.5 mAh/g specific capacity at a high current density of 400 mA/g. The test findings show that 20Li2O–60V2O5–10MoO3–10Fe2O3 efficiently increases high-current responsiveness and cycle stability while retaining a high capacity. In this study, we propose a compositional design strategy, which is based on the coordinated multi-electronic effect of multiple transition metal elements and the design of a stable disordered network structure, to incorporate MoO3 and Fe2O3 into vanadium-based amorphous to create a novel cathode material. This work offers a fresh perspective on investigating innovative lithium-ion battery cathode materials.

Synthesis of 2D VO2 Nanosheets for the Dual Optical Sensor Method by Colorimetric and Fluorometric Sensing of Catecholamines.

For the first time, we report a dual optical sensor method (DOSM) using novel 2D VO2 nanosheets to act as fluorometric and colorimetric sensors to perform quantitative analysis of epinephrine (EP) and dopamine (DA). The wide color spectrum of the 2D vanadium oxidation series and specifically metastable blue 2D VO2 nanosheets were used to develop a DOSM biosensor. DA and EP are the major catecholamines in the human body that play vital roles as neurotransmitters and stress-responsive hormones of the endocrine system, respectively. Accurate and selective detection of these biomolecules can assist in the diagnosis of many neuroendocrine system-related diseases. The newly synthesized 2D VO2 nanosheet sensor showed bluish-green fluorescence as the first-ever fluorescence from 2D VO2 nanosheets. This sensor showed dual-function sensing toward EP by a dominant color change and fluorescence quenching. It is capable of individually detecting and quantifying both EP and DA with high selectivity and sensitivity by using both colorimetry and fluorometry simultaneously, with the detection limits of 1.07 and 5.54 μM for colorimetric analysis, respectively, and 48.07 and 3.98 μM for fluorescence analysis, respectively. The DOSM sensor was directly applied to real urine samples and gained satisfactory recovery above 90% by means of spiked concentrations. This study has opened a new platform using the DOSM and the vanadium oxidation spectrum in a much more effective way for biosensing. The fluorescence capabilities of this metal oxide can be further applied to many sensor applications based on both fluorescence and colorimetric detection.

Effect of para‐Substituents on meso‐Functionalized Oxidovanadium(IV) Porphyrins as Catalysts for Oxygen Atom Transfer Mediated Oxidation of Benzoin to Benzil under Mild Conditions

AbstractSystematic analysis of the effect of para‐substituents (H, Cl, Br and OMe) on the meso‐phenyl group in vanadyl meso‐tetraphenylporphyrins ([VIVO(TPP)] (R=H, 1), [VIVO(TCPP)] (R=Cl, 2), [VIVO(TBPP)] (R=Br, 3) and [VIVO(TMPP)] (R=OMe, 4)) on their properties and catalytic oxygen atom transfer (OAT) for oxidation of benzoin to benzil using DMSO as well as 30 % aqueous H2O2 as the sacrificial oxygen source have been studied. Electrochemical and theoretical (density functional theory) studies are in good agreement with the influence of these substituents on the catalytic property of these complexes. Complex [VIVO(TCPP)] (2) displayed the best catalytic activity for the conversion (92 %) of benzoin to benzil in 30 h with &gt;99 % product selectivity when DMSO was used as an oxygen source, whereas excellent conversion (~100 %) of benzoin to benzil was noticed in 18 h with 95 % product selectivity when 30 % aqueous H2O2 was used as a source of oxygen. Furthermore, among these complexes, the electron‐withdrawing nature of the chloro substituent at the p‐position of meso‐phenyl group significantly influences the oxygen atom transfer. Experimental and simulated EPR studies confirmed the +4 oxidation of vanadium in these complexes. The structure of 2, 3 and 4, confirmed by single crystal X‐ray diffraction method, are domed in shape, and the displacement of V(IV) ion from the mean porphyrin plane follows the order: 2 (0.458 Å) &lt;3 (0.459 Å) &lt;4 (0.479 Å). We observed that the electron‐withdrawing nature of chloro substituent at the p‐position of meso‐phenyl group influence the oxygen atom transfer from vanadyl porphyrin to dimethyl sulfide much.

Utilizing Microelectrodes to Understand Indirect Redox Targeting Reactions for High Energy Density Flow Batteries

One of the major problems with widespread implementation of renewable energy is the lack of cost-effective long-duration grid-scale energy storage filling in for the intermittent nature of solar and wind energy. Redox flow batteries (RFBs) are considered a promising solution to this problem due to their decoupled energy and power capabilities, allowing them to be scaled up for long-duration more efficiently and cost-effectively than other electrochemical energy storage devices [1]. The energy capacity of RFBs is primarily determined by the quantity of active species in the electrolyte, which is a product of the volume and the concentration. Thus, the limiting factor for energy density in RFBs is typically the solubility of the active species [2]. One probable path to enhancing the energy density without increasing the concentration is by utilizing the concept of indirect redox targeting reactions [3]. These redox-targeting flow batteries (RTFB) use solid charge storage materials in the electrolyte tanks to boost capacity, allowing the active species to act as mediators which transfer their charge by reversibly reducing or oxidizing the solid material [4].In this study, cobalt hexacyanoferrate (CoHCF) was used as a solid capacity booster in an electrolyte containing vanadium(iv/v)bis-hydroxyiminodiacetate (VBH) as mediators in acetonitrile. Constant current cycling was performed in a symmetric cell configuration with vanadium ions shuttling between vanadium(iv) and vanadium(v) oxidation states. To monitor the concentration of redox active species accurately and in real-time, a carbon fiber ultramicroelectrode (UME) was installed on the capacity limiting half-cell. This in-line UME set-up provides a better understanding of how CoHCF interacts with mediators and insights on active species crossover between half-cells. In addition, this study aims to examine the kinetics of the indirect redox-targeting reactions. As a rarely studied charge transfer process, very few studies have been reported on the kinetics of indirect redox targeting reactions [5]. Scanning electrochemical microscopy is used to understand how counter cations affect the kinetics of the reaction between the solid booster material and the mediator. Various counter cations (e.g., Ca2+, Na+, Li+) are used with the previously mentioned VBH-based mediators in order to determine the effective rate constants (keff) as well as the reversibility of the charge transfer reactions.