V2O5 Xerogel Research Articles

In situ XRD and Raman study of the phase transition in V2O5 xerogels

Vanadium oxide xerogel samples (V2O5∙nH2O) were successfully synthesized using a liquid phase reaction between α-V2O5 and H2O2, as well as through the interaction of amorphous V2O5 films with atmospheric water. The samples were systematically investigated by X-ray diffraction and Raman spectroscopy. Temperature-dependent studies confirmed the existence of two distinct phases. Depending on synthesis and processing protocols, either phase can be stabilized in ambient conditions. It was proved that the formation of a high-temperature phase from amorphous vanadium oxide previously led to some misinterpretations associated with the high-pressure δ-V2O5 polymorph. While current structural models of vanadium oxide xerogel provide some insights, our findings underscore the exciting potential for refining and expanding these models in future research endeavors.

Reversible Molecular and Ionic Storage Mechanisms in High-Performance Zn0.1V2O5·nH2O Xerogel Cathode for Aqueous Zn-Ion Batteries.

The cathode is a critical component for aqueous Zn-ion batteries (ZIBs) to achieve high capacity and long stability. In this work, we demonstrate a dissolution-free, low-Zn-preinserted bilayer-structured V2O5 xerogel cathode, Zn0.1V2O5·nH2O (ZnVO), with excellent capacity and stability using a low-cost ZnSO4 electrolyte. Its discharge capacity reaches 463 mAh g-1 at 0.2 A g-1 and 240 mAh g-1 at 10 A g-1, while 93% and 88% of its capacity are retained at 0.2 A g-1 for 200 cycles and at 10 A g-1 for 20 000 cycles, respectively. We then show that the outstanding performance of ZnVO is derived from the enlarged gallery spacing by the solvent water intercalation and the water stable V2O5 bilayer structure. We further unveil via ab initio molecular dynamics that H+ is largely originated from the dissociation of the gallery water, while OH- moves out of the gallery to form Zn4(SO4)(OH)6·5H2O with ZnSO4 electrolyte on the surface of ZnVO; the intercalated Zn2+ forms aquo complex [Zn(H2O)6]2+ with the gallery water. Our theoretical analysis also suggests that the gallery water and solvent water in the electrolyte are statistically the same and functionally equivalent. Overall, this study shows the promise of ZnVO as a practical cathode for ZIBs and offers fundamental insights into the roles of gallery water, solvent water, bilayer V2O5 structure, and dual Zn2+/H+ intercalation mechanisms in achieving high capacity and long stability.

Facile synthesis of ultra-large V2O5 xerogel flakes and its application as a cathode material for aqueous Zn-ion batteries

Ultra-large V2O5 xerogel flakes were synthesized by a facile hydrothermal method with commercial V2O5 and H2O2 as raw materials. When evaluated as a cathode material for aqueous Zn-ion batteries in ZnSO4 electrolyte, the ultra-large V2O5 xerogel flakes exhibited superior electrochemical performance with a high specific capacity of 362 mA h g−1 at 100 mA g−1, a rate capacity of 160 mA h g−1 at 1000 mA g−1, and a capacity of 135 mA h g−1 after 200 cycles (corresponding to a capacity-decay rate of 0.18 % per cycle). The apparent Zn2+ diffusion coefficient in the V2O5 xerogel flakes are determined in the order of 10-10 cm2 s−1. Ex-situ XRD and SEM characterizations demonstrate that the V2O5 xerogel flakes well preserve the layered structure upon cycling; besides, Zn3V2O7(OH)2·2H2O phase is detected on the surface of the electrode after cycling due to the dissolution V2O5 in the electrolyte. The superior performance of the sample can be due to the unique ultra-large 2D nanoflake structure which could offer continuous transport paths for both electrons and Zn2+ in the whole flakes and shorten the Zn2+ diffusion length in the direction perpendicular to the flakes.

Fine control over the structure and morphology of metal-matrix composites employing submicron oxide particles with the adjustable redox-activity

It is shown that copolycondensation of mixed vanadic and molybdic acids under the solvothermal conditions yields substitutional solid solution V2O5 : MoO3 (isostructural to V2O5 xerogel) the redox activity of which exhibits increase with the MoO3 content. Thus obtained mixed oxide 0.5V2O5 : 0.5MoO3 with high redox activity, being codeposited with the galvanic nickel, ensure multicenter nucleation of metal phase, yields compact composite with the enhanced corrosion stability.

PEG intercalated vanadium pentoxide xerogel for enhanced sodium storage

Vanadium pentoxide (V2O5) xerogel has attracted much attention as cathode materials for sodium-ion batteries (SIBs) due to its unique layered structure and high theoretical capacity. However, the poor cycling stability and sluggish kinetics severely hamper its practical application. Herein, polyethylene glycol (PEG) intercalated V2O5 xerogel (PEG-V2O5) is fabricated by a facile hydrothermal method. Compared to pure V2O5 xerogel, this PEG-V2O5 xerogel exhibits better cycling stability and enhanced rate capability. For example, the PEG-V2O5 remains a reversible capacity of 110 mAh g−1 after 100 cycles at 100 mA g−1, much higher than that (79 mAh g−1) of the pure V2O5 xerogel; the Na+ diffusion coefficient in PEG-V2O5 is more than two times of that in pure V2O5 xerogel. The expanded interlayer distance, stabilized layered structure, and excellent structure integrity account for enhanced sodium storage performance of the PEG intercalated V2O5 xerogel. This work provides clues for improving the sodium storage performance of V2O5 xerogel from the viewpoint of interlayer engineering.

Synthesis of vanadium oxides nanosheets as anode material for asymmetric supercapacitor

Vanadium oxides (V2O5) have been intensely investigated for advanced supercapacitors due to its extensive multifunctional properties of typical layered structure and multiple stable oxide states of vanadium in its oxides. In this study, V2O5 nanosheets are synthesized via V2O5 xerogel solvothermal reaction in ethanol solvent at 200 °C for 12 h. The V2O5 nanosheets facilitate the easy accessibility of ions and can provide more area available for electrochemical reactions. We have achieved the highest specific capacitance of 298 F/g and good rate discharge for V2O5 electrodes. Notably, the capacitance still retains a high retention rate of 85% after 10,000 cycles at 200 mV/s. Furthermore, asymmetric supercapacitors is assembled based on V2O5 nanosheets and active carbon electrode, and a specific capacitance of 13.2 F/g is obtained at 1 A/g, with a energy density of 4.7 Wh/kg at a power density of 0.798 kW/kg and remains 2.28 Wh/kg at 7.992 kW/kg. Based on these results, the asymmetric supercapacitor exhibits a good cycle life with 77.3% capacitance retention after 3000 cycles. It suggests that the V2O5 nanosheets are promising electrode material for electrochemical supercapacitors.

Effect of hydrogenation on the optical properties and internal electrochromism in vanadium pentoxide xerogel films

The paper describes the effect of hydrogenation of vanadium pentoxide thin films by plasma-immersion ion implantation on their composition, optical properties, and the internal electrochromic (IEC) effect. Variations in the composition and structure caused by the hydrogen insertion, as well as those caused by the electrochromic effect, are studied by nuclear magnetic resonance, thermogravimetry, Raman spectroscopy, and X-ray structural analysis. It is shown that, during electrochromic coloration, if the cathode is located on the non‑hydrogenated region of the film, and the anode is on the hydrogenated region, the IEC effect is more pronounced. This is due to the fact that the migration of protons from the region enriched with hydrogen is considerably greater than that from the pristine non‑hydrogenated region. Thus, the ion implantation-induced hydrogenation can substantially enhance the manifestation and performance of the IEC effect in V2O5 xerogel films. Particularly, the rate of coloration increases by 2–3 times after ion-implantation-assisted hydrogenation as compared to that in the as-prepared non‑hydrogenated films.

Hydrogen photochromism in V2O5 layers prepared by sol–gel technology with the use of dimethylformamide as a hydrogen donor

Here we report on the hydrogen photochromism carried out in the V2O5 xerogels with the use of dimethylformamide (DMF) as a hydrogen donor. The adsorption of DMF was carried out by an original method: DMF was adsorbed on the V2O5 surface along the formation of the xerogel from the sol containing the hydrogen donor. The mechanism of the DMF adsorption on the V2O5 xerogel surface has been discovered by Fourier transform infrared spectroscopy. DMF molecules have been bonded to the oxide surface by donor–acceptor and hydrogen bonds, which pre-determines easy detachment of hydrogen atoms under the action of light. It has been demonstrated that the pronounced hydrogen photocromism can be carried out in the V2O5 xerogels with the use of DMF. The peculiarities of the photochromism have been discussed. The spirit of the research is to provide charging of the V2O5 surface with the hydrogen donor along the formation of the oxide xerogel catalyst.

Modification of the Properties of Vanadium Oxide Thin Films by Plasma-Immersion Ion Implantation

The paper describes the effect of doping with hydrogen and tungsten by means of plasma-immersion ion implantation (PIII) on the properties of vanadium dioxide and hydrated vanadium pentoxide films. It is shown that the parameters of the metal-insulator phase transition in VO2 thin films depend on the hydrogen implantation dose. Next, we explore the effect of PIII on composition, optical properties, and the internal electrochromic effect (IECE) in V2O5·nH2O films. The variations in the composition and structure caused by the hydrogen insertion, as well as those caused by the electrochromic effect, are studied by nuclear magnetic resonance, thermogravimetry, Raman spectroscopy, and X-ray structural analysis. It is shown that the ion implantation-induced hydrogenation can substantially enhance the manifestation and performance of the IECE in V2O5 xerogel films. Finally, the effect of PIII-assisted doping with W on the parameters of electrical switching in Au/V2O5·nH2O/Au sandwich structures is examined. It is shown that implanting small tungsten doses improves the switching parameters after forming. When implanting large doses, switching is observed without electroforming, and if electroforming is applied, the switching effect, on the contrary, disappears.

Enhanced Magnesium-Ion Charge Transport and Storage within Layered Vanadium Pentoxide-Poly(ethylene oxide) Nanocomposites

Cathode materials that have high reversible magnesium-ion capacities and reasonable operating voltages are needed for rechargeable magnesium batteries. Layered materials are a particularly promising class of materials for electrochemical Mg-ion charge storage, however additional research is needed to increase Mg-ion capacities, improve capacity retension upon cycling, and understand the nature of interlayer interactions. Our work has investigated hydrated vanadium pentoxide (V2O5) xerogels that incorporate poly(ethylene oxide) (PEO) between the layers as an approach to improve Mg-ion charge storage and control interlayer structure and dynamics. V2O5 nanosheets were grown in the presence of PEO to allow inimate interaction with the V2O5 layers and allow control of the PEO content in V2O5-PEO nanocomposites. X-ray diffraction and high resolution transmission electron microscopy demonstrate that the interlayer spacing between V2O5 layers was increased by incorporating PEO within the layers. The Mg-ion diffusion coefficient was shown to be strongly dependent on not only interlayer spacing, but also interlayer composition. With specific polymer compositions, Mg-ion diffusion within V2O5-PEO nanocomposites was significantly increased compared with V2O5 xerogels. Raman spectroscopy supports that the polymer interacts with the V2O5 lattice resulting in interlayer water that is less strongly bound to the V2O5 lattice. The V2O5-PEO nanocomposite with specific PEO compositions exhibited significantly improved Mg-ion specific capacity compared with V2O5 xerogels and showed improved capacity retension upon cycling. Our work supports that in addition to interlayer spacing, controlling interlayer interactions between V2O5 layers, PEO, H2O, and Mg-ions allows significant improvements in Mg-ion charge transport and storage. The design of layered materials with controlled interlayer compositions provides a novel route to significantly improve charge storage and transport in layered materials.

Controlling interlayer interactions in vanadium pentoxide-poly(ethylene oxide) nanocomposites for enhanced magnesium-ion charge transport and storage

Abstract Rechargeable magnesium batteries provide the potential for lower cost and improved safety compared with lithium-ion batteries, however obtaining cathode materials with highly reversible Mg-ion capacities is hindered by the high polarizability of divalent Mg-ions and slow solid-state Mg-ion diffusion. We report that incorporating poly(ethylene oxide) (PEO) between the layers of hydrated vanadium pentoxide (V2O5) xerogels results in significantly improved reversible Mg-ion capacities. X-ray diffraction and high resolution transmission electron microscopy show that the interlayer spacing between V2O5 layers was increased by PEO incorporation. Vibrational spectroscopy supports that the polymer interacts with the V2O5 lattice. The V2O5-PEO nanocomposite exhibited a 5-fold enhancement in Mg-ion capacity, improved stability, and improved rate capabilities compared with V2O5 xerogels. The Mg-ion diffusion coefficient of the nanocomposite was increased compared with that of V2O5 xerogels which is attributed to enhanced Mg-ion mobility due to the shielding interaction of PEO with the V2O5 lattice. This study shows that beyond only interlayer spacing, the nature of interlayer interactions of Mg-ions with V2O5, PEO, and H2O are key factors that affect Mg-ion charge transport and storage in layered materials. The design of layered materials with controlled interlayer interactions provides a new approach to develop improved cathodes for magnesium batteries.

Thermodynamics of Metal Cation Intercalation into V2O5(aerogel) Hosts

Sol-gel derived V2O5 (aerogel) is an excellent host for intercalation, showing high capacity for guest species. It was first reported as a host for Li+ ions [1], with a capacity of 4 Li/mole of host [2]. The capacity was shown to be reversible by GITT (galvanostatic intermittent titration technique [3]) for the entire range [1,2,4]. Polyvalent cations were also found to have an intercalation capacity of 4 equivalents/mole of V2O5 aerogel host (i.e. Mg+2, Al+3, and Zn+2) [3,4]. Experimentally, the polyvalent cations were intercalated by chemical insertion from organometallic reagents, in parallel to the chemical insertion technique introduced for Li+ ions [5,6]. Thermodynamics of guest-host systems are of importance to the study of batteries that employ intercalation electrodes. Even though thermodynamics does not specify the capacity of the host materials, the energy state of batteries is dictated for which charge can be extracted and stored. Interaction between the guest species and with the host may diminish the system energy substantially as compared to an ideal guest-host process. The diminished energy leads to a lower usable fraction of the available capacity, as reflected in low voltage or as irreversibility in some materials. Our experience with amorphous V2O5, V2O5 xerogels and crystalline V2O5 as lithium hosts demonstrated that disordered structures are generally preferred for high intercalation capacity hosts. The full usable capacity of four Li (per V2O5 unit) in the V2O5 spin-coated xerogel is not matched with amorphous V2O5 in our studies. This illustrated that with proper processing modified structures can provide a significant enhancement for usable capacity. The structural modification achieved with the V2O5 aerogel revealed that the inherent interaction in the M-V2O5 system is eliminated almost entirely. The discussion here utilizes a model for the interactions as the most significant factor in providing a basis for the high capacity for the multivalent guests in the aerogel material [7,8]. Our analysis of the M-V2O5 systems predicts that the effect of interactions is reduced, to yield model predictions that agree extremely well with the experimental results.

Structural, optical and electrical properties of V2O5 xerogel thin films

Structural, optical and electrical properties of V2O5 xerogel thin films

Nanoscale contact resistance of V2O5 xerogel films developed by nanostructured powder

Here we report the synthesis of V2O5 nanostructures by a fast, simple, cost-effective, low-temperature chemical process; followed by the deposition of V2O5 xerogel thin films on a glass substrate by a sol–gel route. Phase analysis, phase transition, microstructural and electronic characterization studies are carried out by x-ray diffraction, texture coefficient analysis, field emission scanning electron microscopy, transmission electron microscopy (TEM), related selected area electron diffraction pattern (SAED) analysis, Fourier transform infrared spectroscopy, thermogravimetry and differential thermal analysis, differential scanning calorimetry, and x-ray photoelectron spectroscopy techniques. Confirmatory TEM and SAED data analysis prove further that in this polycrystalline powder there is a unique localized existence of purely single crystalline V2O5 powder with a preferred orientation in the (0 1 0) direction. The most interesting result obtained in the present work is that the xerogel thin films exhibit an inherent capability to enhance the intrinsic resistance against contact induced deformations as more external load is applied during the nanoindentation experiments. In addition, both the nanohardness and Young’s modulus of the films are found to be insensitive to load variations (e.g. 1 to 7 mN). These results are explained in terms of microstructural parameters, e.g. porosity and structural configuration.

Internal electrochromism in vanadium pentoxide xerogel films

We describe the internal electrochromic effect in V2O5 xerogel films caused by the redistribution of hydrogen ions inside the film, instead of insertion from the outside, i.e. from an electrolyte, as in the case of conventional electrochromism. A hypothesis is put forward according to which the mechanism of this electrochromic effect is associated with formation of red-colored hexa- and (or) deca-vanadic acid inclusions inside the vanadium pentoxide layers. This model is supported by the calculated data of energy characteristics of V–O chemical bonds in V2O5 octahedra layers of xerogel, as well as by the experimental results of XRD, FTIR, and optical spectroscopy.

Facile synthesis and electrochemical properties of nanoflake VN for supercapacitors

Vanadium nitrides (VN) have drawn much attention due to their large negative potential window, high electronic conductivity and fast reversible redox reaction. The electrochemical performances of VN are affected by their morphology and specific surface area, which depend deeply on the synthesis method. Herein, a large-sized nanoflake V2O5 xerogel is synthesized by a hydrothermal method followed by freeze drying, and then the nanoflake V2O5 xerogel is thermally treated for various times under NH3 atmosphere to study the nitriding process. The results show that the nanoflake V2O5 xerogel is reduced to nanoflake V2O3 before being completely transformed into nanoflake VN. The nanoflake VN demonstrate superior capacitive performance than the nanoflake V2O5 xerogel and intermediate V2O3, which arises from higher intrinsic conductivity.

High Performance Pillared Vanadium Oxide Xerogel Cathode for Lithium Ion Batteries

Lithium ion batteries commonly utilize layered oxide materials as the cathode, where lithium is intercalated and deintercalated between the layers in the crystal structure during cycling. The repeated lithium insertion and extraction can cause stress on the material, leading to fracture. Additionally, the extent of lithiation may cause phase changes in the layered structure that are sometimes irreversible. These changes to the material cause capacity loss and reduce the battery cycle life. This research focuses on nanostructuring layered oxides to enhance their cyclability and power capabilities. In particular, vanadium oxide xerogels were modified by adding pillaring molecules between the layers to increase the interlayer spacing. Vanadium oxide xerogels possess attractive capacities but suffer from significant capacity fade due to distortion of the crystal structure. We hypothesize that the pillars will enhance thermal and mechanical stability by reducing the strain on the structure and increasing lithium ion mobility, thereby increasing the cycle life and high rate capacities. Aluminum Keggin ions were used as pillaring agents for the vanadium oxide xerogels. X-ray diffraction showed an interlayer spacing increase from 1.14 to 1.32 nm after pillaring, consistent with the size of the keggin ions (~1.3 nm), while still maintaining the layered V2O5 xerogel crystalline structure (Figure 1). Elemental analysis indicated an aluminum loading of 9 wt% in the pillared material. The pillared materials also demonstrate increased thermal stability and rate capabilities during cycling in coin cells, with capacities over 60% higher than those of the unpillared V2O5 xerogel. Additionally, the pillared materials retained more capacity during cycling at C/2. Pillaring the layered vanadium oxide xerogels improved both capacity retention and battery lifetime. Figure 1. Diffraction patterns for V2O5 xerogel (a), pillared V2O5 xerogel (b), and pillared V2O5 xerogel after heat treatment in either air (c) or nitrogen (d). The dotted line is intended as a guide for the eye. Figure 1

Effect of the Composition and Post-Synthesis Heat Treatment on the Electrochemical Characteristics of Polypyrrole/V2O5 Nanocomposites Prepared by a Mechanochemical Method

Effects were shown for the composition and post-synthesis heat treatment in an oxygen atmosphere on the electrochemical properties of nanocomposites derived from polypyrrole (PPy) and a V2O5 xerogel with host–guest structure. PPy0.05V2O5 was found to have the highest specific discharge capacity of about 290 mA·h/g and high stability upon prolonged charge-discharge cycling among the PPyxV2O5 nanocomposites prepared (where x = 0.1, 0.05, 0.025). Post-synthesis heat treatment in an oxygen atmosphere leads to oxidation of the reduced portion of the inorganic nanocomposite component and nanostructurization of the composite with formation of nanofibers that facilitate a considerable increase in the specific capacity and stability upon cycling.

Electrode Performance of Sulfur-Doped Vanadium Pentoxide Gel Prepared by Microwave Irradiation for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries have attracted attention for use in the nextgeneration power storage applications. V2O5 xerogel, which has a high capacity, is expected to be an active cathode material for magnesium rechargeable batteries. However, it faces the problem of degradation due to desorption of structural water. A vanadium pentoxide xerogel containing sulfur (S-V2O5 gel) was prepared by a new composition process and evaluated by structural analysis, and its electrode performance was analyzed. Structural analysis by X-ray diffraction, differential thermal analysis, and scanning electron microscopy showed that the bulk S-V2O5 gel adopted a V2O5 xerogel-like structure with a layer structure in a stable planar direction with added sulfur, and that the surface was a reformed hard amorphous structure due to treatment with a low-temperature plasma generated using carbon felt (CF-MWP). Charge-discharge tests revealed a specific capacity of 450 mAh g-1, and cyclic voltammetry was almost perfectly stabilized after the second cycle. Keywords: Cathode Material, microwave, rechargeable magnesium battery, sulfur doped, vanadium pentoxide, xerogel.

Soft-template synthesis of vanadium oxynitride-carbon nanomaterials for supercapacitors

By using Polyvinylpyrrolidone (PVP) as the soft-template, vanadium oxynitride-carbon (VOxNy-C) nanomaterials were synthesized by NH3 reduction of V2O5 xerogel. The powder X-ray diffraction result indicated that the VOxNy-C belongs to the cubic crystal system. Transmission electron microscopy (TEM) images showed that most of the VOxNy grains in VOxNy-C materials were lower than 20 nm. Electrochemical test results showed that VOxNy-C materials exhibited better conductivity and enhanced electrochemical properties compared to VOxNy materials which were synthesized only by NH3 reduction of V2O5 xerogel. The maximum specific capacitance of VOxNy-C electrode reaches up to 271 Fg−1 at 1 Ag−1 which is much higher than that of VOxNy electrode (143 F g−1). The specific capacitance of VOxNy-C electrode lost less than 10% as the scan rate increased 20 times from 5 to 100 mV s−1, showing its superior rate capability. The VOxNy grains and remaining carbon were intimate contact each other in VOxNy-C nanocomposite which results in a better electronic conductivity, as well as the high surface area which furnishes more surface active redox sites of VOxNy-C nanocomposite. Therefore, VOxNy-C material exhibited better electrochemical performance than VOxNy. Cycle tests showed that restricting the potential window can improve the cycling stability of the VOxNy-C electrode. This cycle phenomenon may be ascribed to the use of high upper potentials which lead to the irreversible oxidation of electrode materials and the concomitant formation of soluble vanadium based species, which further result in the reduction of the active redox sites, and ultimately enhance the electrode's irreversibility in 1 M KOH.