**Abstract**

The first synthesis of pentoxide vanadium (V2O5) as gel completed 135 years in 2020. Since its first synthesis, the V2O5 has attracted attention over the years in different areas in science and technology. There are several possibilities to obtain V2O5 resulting in different structures. Among these methods, it is possible to mention the sol–gel, hydrothermal/solvothermal synthesis, electrospinning, chemical vapor deposition (CVD), physical vapor deposition (PVD), template-based methods, reverse micelle techniques, Pechini method and electrochemical deposition that can be considered as the great asset for its varied structures and properties. Progress towards obtaining of different structures of V2O5, and phases have been resulted in lamellar structure with wide interlayer spacing, good chemical and thermal stability and thermoelectric and electrochromic properties. Throughout this advancement, its performance for industrial applications have made a strong candidate in electrochromic devices, photovoltaic cell, reversible cathode materials for Li batteries, supercapacitor, among others. This chapter will be to assist an updated review since the first synthesis up to current development.

**Keywords:** V2O5, obtaining methods, structures, applications

### **1. Introduction (Historical and sources)**

The discovery of vanadium was marked by uncertainty and confusion due to its chemical similarity with some elements. In 1801, the Spanish mineralogist, Andrés Manuel Del Rio, discovered an element with the atomic number 23, in Mexico, in a lead mineral. Due to the similarity of its colors to those of chrome, Del Rio called this element as panchrome. Later, after noting that the color of these salts turned red when heated, he renamed it as erythron. However, Del Rio withdrew his claim when, four years later, it was suggested by the French chemist, Hippolyte Victor Collett-Desotils, that the mineral was really an impure chromium, provoking the retraction of Andrés Manuel Del Rio [1]. In 1830, Swedish chemist Nils Gabriel Sefström rediscovered the element in an oxide that it was found while working at an iron mine and gave it the name by which it is known today. A year later, in 1831, Friedrich Woehler confirmed that this element was the same already discovered by Del Rio in 1801. In 1867, Henry Enfield Roscoe, an English chemist, isolated it almost purely by reducing the chloride with hydrogen [1]. The name vanadium refers to the goddess of beauty in Scandinavian mythology Vanadis, also known as Freya, due to the beautiful variation in the color of its compounds. Vanadium

is the nineteenth most abundant element in the earth's crust (136 ppm), and the fifth among transition metals. Despite being a metal considered abundant, it is not found in its elemental form, but it is present in approximately 65 different minerals, among which stand out vanadinite, PbCl2.3Pb3 (VO4)2, carnotite, K2(UO2)2(VO4)2.3 H2O, roscoelite K(V3AlMg)2(SiAl)4O10(OH)2 and patronite, V2S3 [2]. Of the world's vanadium resources, most are present in magma, located in the Bushveld volcanic complex in South Africa, which has the world's largest reserves of iron/vanadium, followed by Russia, the United States and China. In 2019, about 90% of vanadium was obtained from magnetite and titanomagnetite ores. Regarding vanadium production, China led the largest global production of 2019 through slag. Asia China is the world's largest producer of vanadium, with 59%, followed by Russia accounting for 17% and South Africa with 7% of the global supply of vanadium. Most of its vanadium was derived from the primary production of Bushveld Minerals and Glencore. The most commercially available vanadium products are vanadium pentoxide and iron-vanadium. Vanadium pentoxide is obtained by treating magnetite iron ores and slag.

### **2. Structures of vanadium oxides**

The system of V-O has different oxidation states with V2O5 being the most stable. This system occurs from V2+ to V5+ such as vanadium monoxide (VO), vanadium sesquioxide (V2O3), vanadium dioxide (VO2) and vanadium pentoxide (V2O5). Besides, it is possible to obtain mixed valence oxides that present several of oxides containing V5+/V4+ mixture (in V3O7, V4O9, and V6O13) and V4+/V3+ mixture (in V6O11, V7O13, and V8O15 [3]. From these mixing phases is possible to form two phases called as Magnéli phase (VnO2n-1) and Wadsley phase (VnO2n + 1). A schematic V-O phase diagram calculated by Kang [4] presented the Magnéli phase as being V6O13, V3O7, V2O5 as well as Wadsley phase V3O5, V4O7, V5O9, V6O11, V7O13 and V8O15. The phases and structures in the V-O phase diagram is depicted in **Table 1**.

From the **Table 1**, it is possible to observe that the V-O system can exhibits multiples crystalline structures. These crystalline structures can be modified considering the oxygen fractions in the range 0.5–0.75 and decrease of formation energy (eV.atom−1). It is worth mentioning that formation energy between the stable and metastable phases ranges, for example, between 4 meV in V2O5 and 35 meV in V2O3, making possible a reversible structural transition [5]. The Magnéli phase (VnO2n-1, with *n* = 4 to 9) is considered as being rutile-type with VO6 octahedral [6]. The increase of *n* in VnO2n-1 compounds might has an inherent effect on the magnetic and electric properties.

On the other hand, Wadsley phase, (VnO2n + 1, with *n* = 1 to 6) is known as layered vanadium oxides. This V-O phase has single and double layers being able to accommodate V4+ cations and both V4+/V5+ cations, respectively [5, 7, 8]. The presence of these layers makes it possible to intercalate different ions which makes them suitable for energy conversion and storage [9]. Besides, mixed valence in Wadsley phase can be formed by introducing oxygen vacancy. The oxygen vacancy can generate mixed oxidation state with two oxidation states. It is possible to point out V6O13 with V5+/V4+ as well as VO2, V2O3, V8O15, V7O13, V6O11 with V4+/V3+ species.

The most famous and stable of the layered VnO2n + 1 is V2O5. Along the xyz axis (3D) V2O5 presents a V chains forming a network with oxygen which results as VO5 pyramids [6]. X-ray diffraction (XRD) pattern of orthorhombic V2O5 and a layered crystalline structure has a standard pattern number JCPDS No. 41–1426 [10]. That way, its structure is orthorhombic with parameters a = 1.151 nm, b = 0.356 nm and c = 0.437 nm. From xy axis, V-O layer-like structure with two oxygen in z axis

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*Vanadium Pentoxide (V2O5): Their Obtaining Methods and Wide Applications*

tetragonal tetragonal orthorhombic orthorhombic orthorhombic monoclinic cubic trigonal

monoclinic orthorhombic

V3O7 monoclinic C2/c

orthorhombic orthorhombic orthorhombic monoclinic monoclinic monoclinic triclinic

monoclinic

V4O7 Triclinic P1 V5O9 Triclinic P1 V6O11 Triclinic P1 V7O13 Triclinic P1 V8O15 Triclinic P1

**Phase Lattice Space group** VO Cubic Fm3m

> P42/mnm I4/mmm I41/a Pmnn Pmcn Pnmb C2/m Fd3m R3m

Cm C2/m Fmmm

Pmnm Pmnb Pmna Cmcm P21/m C2/m C2/c P1

P2/c C2/c

forming a distorted trigonal bipyramidal coordination polyhedral. Each combination of VO5 pyramids has planes (00 l) and V is linked with five oxygen atoms by single bonds being four oxygen in xy axis and one oxygen in z axis. Then, in series of planes of VO5 are connected with alternating oxygen position in z axis (perpendicular) according to the sequence two up and two down. Therefore, the V-O single bond in perpendicular position presents a weak interaction compared to oxygen located in adjacent layer [7, 11]. This layered characteristic makes enable an introduction of several ions into the lamellar spacing which bringing change of the crystalline

V-O bonds from V2O5 have different distance caused by spontaneous deformation of the geometry to reduce the energy of the system. Then, vanadyl bond with four oxygen from the plane present a value of 0.178 nm. The bond of the extension along the z axis has 0.279 nm and the vertical axis opposite to the V–O bond has 0.158 nm. Depending on the conditions, vanadium oxidation states might range of V2+ to V5+ as well as changes in coordination geometrics. Structural evolution in function of pH and concentration of V2O5 precursors are responsible by different oxidation

structure resulting in different properties (**Figure 1**).

*DOI: http://dx.doi.org/10.5772/intechopen.96860*

VO2 tetragonal

V6O13 monoclinic

V2O5 orthorhombic

V3O5 monoclinic

*Examples of phases and structures of V-O phase diagram.*

**Magnéli**

**Wadsley**

**Table 1.**


*Vanadium Pentoxide (V2O5): Their Obtaining Methods and Wide Applications DOI: http://dx.doi.org/10.5772/intechopen.96860*

#### **Table 1.**

*Examples of phases and structures of V-O phase diagram.*

forming a distorted trigonal bipyramidal coordination polyhedral. Each combination of VO5 pyramids has planes (00 l) and V is linked with five oxygen atoms by single bonds being four oxygen in xy axis and one oxygen in z axis. Then, in series of planes of VO5 are connected with alternating oxygen position in z axis (perpendicular) according to the sequence two up and two down. Therefore, the V-O single bond in perpendicular position presents a weak interaction compared to oxygen located in adjacent layer [7, 11]. This layered characteristic makes enable an introduction of several ions into the lamellar spacing which bringing change of the crystalline structure resulting in different properties (**Figure 1**).

V-O bonds from V2O5 have different distance caused by spontaneous deformation of the geometry to reduce the energy of the system. Then, vanadyl bond with four oxygen from the plane present a value of 0.178 nm. The bond of the extension along the z axis has 0.279 nm and the vertical axis opposite to the V–O bond has 0.158 nm.

Depending on the conditions, vanadium oxidation states might range of V2+ to V5+ as well as changes in coordination geometrics. Structural evolution in function of pH and concentration of V2O5 precursors are responsible by different oxidation

**Figure 1.** *Perspective view of two layers of V2O5. Weak van der Waals bonds are omitted for clarity.*

**Figure 2.** *Structures polymorphs of V2O5.*

states. Whenever a decrease of pH (13 to 1) and increase of H<sup>+</sup> /V (1 to 3 and concentration range from 10−3 to 10−1 mol.L−1) there are predominant species such as pyrovanadate, metavanadates, decavanadates, respectively. The main reaction that occurs during the formation of V2O5 are called olation and oxolation which will be detailed in Section 3.

It is possible to find V2O5 as α, β, and γ polymorphs (**Figure 2**) and among them have four orthorhombic, two monoclinic and one triclinic phase. α-V2O5 is a stable phase with an interlayer spacing of 0.452 nm. After a distortion forming by VO6 in the V2O5 structure, V atoms are dislocated to the corner from the middle forming β-V2O5. γ-V2O5 presents oxygen alternated up and down pyramids connected with vanadium in the center and each VO5 square pyramids forming zig-zag structure. There is a V=O bond along z axis that presents a weak bond and a covalent bond along x and y axis, creating double layers of O-V-O which is considered as short and strong. These torsion on structure makes γ-V2O5 more flexible and results in a structure metastable [12, 13].

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*Vanadium Pentoxide (V2O5): Their Obtaining Methods and Wide Applications*

**3. Structure of V2O5 based on its obtaining methods**

nanomaterial, thin films, porous materials, among others.

The double layers of O-V-O are separated by van der Waals bond being a weak one. The different bonds along the coordinates of V2O5 creating a strong anisotropic in the V2O5 as 2-D layered material. Then, the basal plane (010) presents lower surface energy compared to (100) and (001) planes. As V2O5 presents plane as stacking of playing cards with weak interlayer force, it is possible to provides an intercalation

In this section various conditions of synthesis and preparation methodology will be approached as well as their structural influences on V2O5. The interesting of V2O5 is focused on its versatility in several applications based on obtaining methods. The most used preparation technique is sol–gel but other methods such as hydrothermal/solvothermal synthesis, electrospinning, chemical vapor deposition (CVD), physical vapor deposition (PVD), template-based methods, reverse micelle techniques, Pechini method and electrochemical deposition can be used as well. Often, combinations of these methods can be found to obtain different structures of V2O5. The control of reaction conditions allows the formations of V2O5 as powder,

*Sol–gel* – The sol–gel method (or synthesis or process) is basically based on hydrolysis and condensation of precursor material. This method was reported by Ditte in 1885 [14] that observed a formation of a red sol when the ammonium vanadate precursor was heated with nitric acid and water inside of platinum crucible. Other similar experiments were published some years later by Blitz [14]. During the sol–gel process the formation of V2O5 occurs during the olation and oxolation stages in pH 2 (**Figure 3**). Throughout the olation, the V5+ central is hexacoordinate with water and, opposite side, oxygen with double bond in z axis. Other four bonds are orientated in the equatorial plane which x axis occur water and -OH bonds in opposite sides. Finally, in y axis there are two bonding of -OH in opposite sides. Due to distortion in the structure the length of bonds is not equal and the release of water molecule from x axis occurs resulting in the connection between V5+ central link with oxygen from the other molecule coordinate forming the olation chain polymers. After the olation occurs a reaction in z axis called oxolation. The oxolation lead to the formation of edge sharing double chains in y axis. During this stage occurs a condensation resulting in polymerization of (-O-V-O′-)n, which linked together whit O′ from other -O′-V- molecule coordinate. Finally, orderly planes along the y axis of polymerized VOx are formed and connected by Van der Waals force. Other planes are generating a lamellar structure with interlayer distance around 1.17 nm [15]. Through this interlayer spacing, it is possible to perform an intercalation reaction of different substances without interfering in the crystallinity of V2O5 (topotactic process) [15–18]. Intercalation reactions yield new materials with different or improved properties (synergic effect). V2O5 obtained from sol–gel synthesis has low viscosity, reddish brown color and after dry in room temperature is formed a xerogel of V2O5 thin film. The properties will be discussed in Section 4. *Hydrothermal/solvothermal synthesis* – Hydrothermal and solvothermal synthesis or method is widely used in inorganic synthesis. This method is often carried out in an autoclave with high-temperature aqueous solutions at high vapor pressures. Then, hydrothermal method can be defined as a method of synthesis of crystals or particles that depends on the solubility of inorganic material in hot solution under high pressure. V2O5 obtained from hydrothermal synthesis is a powder solid and generally use a salt of metavanadate. The V2O5 power presents an orthorhombic oxide α-V2O5 that exhibits a layered structure made of edge and corner sharing

*DOI: http://dx.doi.org/10.5772/intechopen.96860*

reaction with several substances [12].

The double layers of O-V-O are separated by van der Waals bond being a weak one. The different bonds along the coordinates of V2O5 creating a strong anisotropic in the V2O5 as 2-D layered material. Then, the basal plane (010) presents lower surface energy compared to (100) and (001) planes. As V2O5 presents plane as stacking of playing cards with weak interlayer force, it is possible to provides an intercalation reaction with several substances [12].
