Vanadium Oxide: Phase Diagrams, Structures, Synthesis, and Applications

Vanadium oxides with multioxidation states and various crystalline structures offer unique electrical, optical, optoelectronic and magnetic properties, which could be manipulated for various applications. For the past 30 years, significant efforts have been made to study the fundamental science and explore the potential for vanadium oxide materials in ion batteries, water splitting, smart windows, supercapacitors, sensors, and so on. This review focuses on the most recent progress in synthesis methods and applications of some thermodynamically stable and metastable vanadium oxides, including but not limited to V₂O₃, V₃O₅, VO₂, V₃O₇, V₂O₅, V₂O₂, V₆O₁₃, and V₄O₉. We begin with a tutorial on the phase diagram of the V-O system. The second part is a detailed review covering the crystal structure, the synthesis protocols, and the applications of each vanadium oxide, especially in batteries, catalysts, smart windows, and supercapacitors. We conclude with a brief perspective on how material and device improvements can address current deficiencies. This comprehensive review could accelerate the development of novel vanadium oxide structures in related applications.

Kerr-nonlinearity-assisted NIR nonreciprocal absorption in a VO2-based core-shell composite integrated with 1D nonlinear multilayers

We theoretically investigate the nonreciprocal optical response of a one-dimensional multilayer possessing nonlinear (NL) Kerr dielectrics hybridized with a VO₂-based core-shell structure. As a consequence of parameter optimization, it is found that semiconductor-to-metallic reconfiguring of relatively thin VO₂ nanoinclusions with a core-shell radius ratio of 0.95 is accompanied by enhanced multispectral near-infrared absorption of the system for both forward and backward incidences of light. However, increasing intensity of the incident wave bends the resonant wavelengths due to the NL response of Kerr dielectrics. When the incident light is well set up for an appropriate non-resonant wavelength, the absorption contrast between two directions of incidence enhances in some ranges of intensities due to the NL Kerr effect. There is also the possibility of reaching S-shaped bistable absorption. These features make the modeled system suitable for designing near-infrared absorptive diodes or isolators.

V3S4 Nanosheets Anchored on N, S Co-Doped Graphene with Pseudocapacitive Effect for Fast and Durable Lithium Storage

Construction of a suitable hybrid structure has been considered an important approach to address the defects of metal sulfide anode materials. V₃S₄ nanosheets anchored on an N, S co-coped graphene (VS/NSG) aerogel were successfully fabricated by an efficient self-assembled strategy. During the heat treatment process, decomposition, sulfuration and N, S co-doping occurred. This hybrid structure was not only endowed with an enhanced capability to buffer the volume expansion, but also improved electron conductivity as a result of the conductive network that had been constructed. The dominating pseudocapacitive contribution (57.78% at 1 mV s⁻¹) enhanced the electrochemical performance effectively. When serving as anode material for lithium ion batteries, VS/NSG exhibits excellent lithium storage properties, including high rate capacity (480 and 330 mAh g⁻¹ at 5 and 10 A g⁻¹, respectively) and stable cyclic performance (692 mAh g⁻¹ after 400 cycles at 2 A g⁻¹).

Controlled synthesis of 3D porous VO2(B) hierarchical spheres with different interiors for energy storage

3D VO₂(B) hollow spheres exhibit better electrochemical properties, including specific capacitance, areal energy density and cycling stability, than VO₂(B) solid spheres.

Component-Customizable Porous Rare-Earth-Based Colloidal Spheres towards Highly Effective Catalysts and Bioimaging Applications

Multicomponent porous colloidal spheres are of interest because they not only show a combination of the properties associated with all different components, but also usually present synergy effects. However, a combination of different components in a single porous sphere is still greatly challenged due to the different precipitation behaviors of each component. In this work, we have developed a general synthetic route to prepare several categories of porous monodisperse rare-earth (RE)-based colloidal spheres with customizable elemental compositions and a uniform element distribution. The two-step synthetic strategy is based on the integration of coordination chemistry precipitation of RE ions and a subsequent ion-exchange process, which steers clear of obstacles, such as differences in solubility product constant, that are to be found in traditional co-precipitation methods. Our approach provides a new mixing mechanism to realize homogeneous distribution of each element within the porous spheres. An array of binary, ternary, and even senary RE colloidal porous spheres with diameters of 500 nm to 700 nm has been successfully synthesized. Taking advantage of their good dispersibility, porosity, and customizable components, these porous RE oxide spheres show excellent catalytic activity for the reduction of 4-nitrophenol, and promising application in single-phase multifunctional bioprobes.

Influence of VO₂ Nanoparticle Morphology on the Colorimetric Assay of H₂O₂ and Glucose

Nanozyme-based colorimetric sensors have received considerable attention due to their unique properties. The size, shape, and surface chemistry of these nanozymes could dramatically influence their sensing behaviors. Herein, a comparative study of VO₂ nanoparticles with different morphologies (nanofibers, nanosheets, and nanorods) was conducted and applied to the sensitive colorimetric detection of H₂O₂ and glucose. The peroxidase-like activities and mechanisms of VO₂ nanoparticles were analyzed. Among the VO₂ nanoparticles, VO₂ nanofibers exhibited the best peroxidase-like activity. Finally, a comparative quantitative detections of H₂O₂ and glucose were done on fiber, sheet, and rod nanoparticles. Under the optimal reaction conditions, the lower limit of detection (LOD) of the VO₂ nanofibers, nanosheets, and nanorods for H₂O₂ are found to be 0.018, 0.266, and 0.41 mM, respectively. The VO₂ nanofibers, nanosheets, and nanorods show the linear response for H₂O₂ from 0.025-10, 0.488-62.5, and 0.488-15.625 mM, respectively. The lower limit of detection (LOD) of the VO₂ nanofibers, nanosheets, and nanorods for glucose are found to be 0.009, 0.348, and 0.437 mM, respectively. The VO₂ nanofibers, nanosheets, and nanorods show the linear response for glucose from 0.01-10, 0.625-15, and 0.625-10 mM, respectively. The proposed work will contribute to the nanozyme-based colorimetric assay.

Hydrothermal Synthesis of VO2 Polymorphs: Advantages, Challenges and Prospects for the Application of Energy Efficient Smart Windows

Vanadium dioxide (VO₂ ) is a widely studied inorganic phase change material, which has a reversible phase transition from semiconducting monoclinic to metallic rutile phase at a critical temperature of τ_c ≈ 68 °C. The abrupt decrease of infrared transmittance in the metallic phase makes VO₂ a potential candidate for thermochromic energy efficient windows to cut down building energy consumption. However, there are three long-standing issues that hindered its application in energy efficient windows: high τ_c , low luminous transmittance (T_lum ), and undesirable solar modulation ability (ΔT_sol ). Many approaches, including nano-thermochromism, porous films, biomimetic surface reconstruction, gridded structures, antireflective overcoatings, etc, have been proposed to tackle these issues. The first approach-nano-thermochromism-which is to integrate VO₂ nanoparticles in a transparent matrix, outperforms the rest; while the thermochromic performance is determined by particle size, stoichiometry, and crystallinity. A hydrothermal method is the most common method to fabricate high-quality VO₂ nanoparticles, and has its own advantages of large-scale synthesis and precise phase control of VO₂ . This Review focuses on hydrothermal synthesis, physical properties of VO₂ polymorphs, and their transformation to thermochromic VO₂ (M), and discusses the advantages, challenges, and prospects of VO₂ (M) in energy-efficient smart windows application.

Hierarchical Mesoporous Iron Fluoride with Superior Rate Performance for Lithium-Ion Batteries

Monodispersed mesoporous iron fluorides were synthesized by a low-cost reversed micelle method. The as-prepared materials with hierarchical mesoporous structure exhibit excellent rate capability (115.6 mAh g^-1 at 2000 mA g^-1) which is superior to many other carbon-free iron fluorides. In addition, a high reversible capacity of 143.2 mAh g^-1 can be retained after 100 cycles at 1000 mA g^-1. The outstanding electrochemical features can be attributed to the particular hierarchical mesoporous structure, facilitating electrolyte penetration as well as rapid electronic and ionic transportation.

Porous V2O5/RGO/CNT hierarchical architecture as a cathode material: Emphasis on the contribution of surface lithium storage

A three dimensional vanadium pentoxide/reduced graphene oxide/carbon nanotube (3D V₂O₅/RGO/CNT) composite is synthesized by microwave-assisted hydrothermal method. The combination of 2D RGO and 1D CNT establishes continuous 3D conductive network, and most notably, the 1D CNT is designed to form hierarchically porous structure by penetrating into V₂O₅ microsphere assembly constituted of numerous V₂O₅ nanoparticles. The highly porous V₂O₅ microsphere enhances electrolyte contact and shortens Li⁺ diffusion path as a consequence of its developed surface area and mesoporosity. The successive phase transformations of 3D V₂O₅/RGO/CNT from α-phase to ε-, δ-, γ-, and ω-phase and its structural reversibility upon Li⁺ intercalation/de-intercalation are investigated by in situ XRD analysis, and the electronic and local structure reversibility around vanadium atom in 3D V₂O₅/RGO/CNT is observed by in situ XANES analysis. The 3D V₂O₅/RGO/CNT achieves a high capacity of 220 mAh g⁻¹ at 1 C after 80 cycles and an excellent rate capability of 100 mAh g⁻¹ even at a considerably high rate of 20 C. The porous 3D V₂O₅/RGO/CNT structure not only provides facile Li⁺ diffusion into bulk but contributes to surface Li⁺ storage as well, which enables the design of 3D V₂O₅/RGO/CNT composite to become a promising cathode architecture for high performance LIBs.

Synthesis of hierarchical nanosheet-assembled V2O5 microflowers with high sensing properties towards amines

Hierarchical three-dimensional nanosheet-assembled vanadium pentoxide (V₂O₅) microflowers are successfully synthesized by a hydrothermal method, followed by a high-temperature sintering treatment.