**4.2 Lithium-ion batteries**

*Transition Metal Compounds - Synthesis, Properties, and Application*

lithium-ion batteries as potential anode material. Furthermore, using controlled chemical etching, hollow interiors could be generated inside the PB nanoparticles in poly (vinylpyrrolidone) presence, [96] porous nanostructures of iron oxide having hollow interiors, various phases of these PB nanoparticles (preliminary precursors)

*Morphology of the hollow spheres composed of ZnO nanorods. (a) TEM image of the samples (b, c) typical magnified TEM images of hollow spheres (d, e) SEM image of the samples (f) typical magnified SEM image* 

Due to the potential uses in various fields like waste removal, biologically active agent protection, chemical, biological sensors, catalysis, and bimolecular-release systems, well-defined 0-D ZnO hollow structures have attracted much attention. So in past few years, many successful attempts were made to prepare hollow structures of ZnO. The template-assisted technique is now the main focus of researchers which conventionally employed spherobacteria, carbon spheres, polystyrene spheres, and so on as template for hollow structures growth of ZnO. Under hydrothermal conditions,

ZnO formation which have an inner and outer diameter as 100 nm and 600 nm, respectively. These hollow spheres were made up of ZnO nanorods (**Figure 9**). Ethanol volume ratio with respect to solution and initial mixture pH value both have a significant role in hollow spheres formation. Meanwhile, results obtained from characterization, ZnO hollow spheres showed remarkable photoluminescence

Over the past decade, due to unique electronic, magnetic, and optical applications metal oxide materials arising as potential candidates with fruitful functionalities have been extensively studied. These applications will be discussed briefly in this section.

In photovoltaics stable and environment-friendly metal oxide semiconductors are used in dye−sensitized solar cells (DSSCs) as photoelectrode or to design p-n

properties (at room temperature) with UV emission peak at 390 nm.

4) <sup>+</sup> reported by Gao *et al.* [97] resulted in hollow spheres of

can be synthesized by controlled calcination.

*of a hollow sphere (g) the EDS spectrum of hollow spheres [98].*

conversion of Zn(NH3 <sup>2</sup>

**Figure 9.**

**4. Advanced applications**

**4.1 Photovoltaics**

**14**

In technology, lithium-ion batteries made up of metal oxide nanoparticles (SnO2, Co3O4, Fe2O3, TiO2, and complex metal oxides) enable superior rate capability; better cycling performance and high specific capacity are arising as the best choice for portable electronics. Its applications include electronics, electric vehicles, etc. Transition metal oxides hold boundless potential towards high-energy-density anode due to their better capacities than those which are commercially utilized as anode material such as graphite [2, 101, 102].

## **4.3 Photocatalysis**

In most highlighted photocatalytic areas TiO2 has been the most promising material as a photocatalyst. In last 3 decades, TiO2 attracted notable scientific and technological consequences (**Figure 11**). Similarly, to study other photocatalytic oxidation properties metal oxides (ZnO, SnO2, Fe2O3, WO3, Cu2O, SrTiO3) have been studied in detail. High crystallinity and large surface area with more active sites reduce recombination rate of photo−generated electron–holes pairs are the properties of the best photocatalyst. For oxygen (O2) evolution by photocatalysis from H2O under irradiation of visible light, highly−arranged tungsten oxide (m − WO3) hybridized with reduced graphene-oxide has been synthesized. Tremendous photocatalytic properties have been shown by CdS nanorods/reduced graphene-oxide composites had excellent photocatalytic properties with a rate constant was around three times greater than CdS nanorods for the degradation of MO [2, 103].

### **4.4 Gas-sensing**

Electrical conductance sensitive to ambient gas composition, rising from interactions of charges with volatile organic compounds, reactive gases (O2, CO, NOx), hydrocarbons, and semiconducting metal oxides (WO3, TiO2, SnO2, ZnO) are utilized for gas sensing applications. The effort was made to acquire better results towards low pollutant gas concentrations under low operating temperatures for gas sensing materials. For the detection of harmful gases and large scale, thermal stability under operating conditions of sensors SnO2 nanostructures has attracted the most attention [2, 104].

**Figure 10.**

*Schematic diagram of the nanowire dye-sensitized solar cell based on a ZnO wire array [99].*

**Figure 11.**

*Scheme of photo-induced processes at a TiO2 semiconductor/electrolyte interface [103].*

#### **4.5 Biomedical**

In biomedical field, magnetic metal oxides have been used with biological agents, have excellent applications. As superparamagnetic Fe3O4 can act as potent nanoprobes magnetic fluid hyperthermia (MFH), biosensors, magnetic resonance imaging (MRI) are biocompatible and stable chemically as well as magnetically. For therapy and targeted drug delivery, Ferrite MFe2O4 (where M = Mn, Zn, Ni, Co, etc.) has also been characterized and studied [105–107].

#### **5. Outlook, challenges, and a little science fiction**

The synergic effects and complex chemical configurations of several metal species in the TMOs induce noteworthy electrochemical performance. Numerous elegant approaches including compositions and manipulation of the micro/nanostructures have been widely established, that aims to endorse utilization of TMOs in everyday energy conversion technologies and enhancement of electrochemical performance. However, each designed approach applies lonely that normally consequences in partial enhancement in of electrodes based upon TMOs with respect to their electrochemical performance. Thus, it is more fascinating to assimilate manifold stimulating design approaches, therefore aggregating their electrochemical performance to meet today's energy demands.

The mainstream of research reports owing to the utilization of TMOs related to boost energy storage devices is primarily based on the observations of a specific experiment. A wide-ranging insight into the connection among the composition (structure) and properties of these TMOs that are related to their performance has not been systematically attained yet. Thus, effective and reliable methods and standards are necessary to develop urgently to assess the energy storage devices that are based on TMOs. Theoretical simulation and mathematical modeling are also greatly anticipated to be established in order to direct large-scale, low-cost, and facile fabrication along with the purposeful design of TMOs for greater electrochemical performance.

Realizing the unsuccessful mechanisms upon cycling in the electrodes based upon TMOs for LIBs is crucial to direct the scheme and design of progressive materials. This needs to understand the compositional parameter and structural evolution as well as consideration of electrolyte compatibility matter. The amendment of electrolytes including certain reversible redox-couples (as additives) in aqueous electrolytes has been demonstrated that could considerably progress the general electrochemical progress of pseudo-capacitive materials. Thus, we also assume that appropriate scheme and design of electrolytes could additionally elevate the electrochemical performance of TMOs for both rechargeable batteries. Additionally,

**17**

*Rational Design and Advance Applications of Transition Metal Oxides*

the assessment of pseudo-capacitive progress of TMOs is generally accomplished in aqueous electrolytes. This accomplishment is unescapably restricts the energy density owing to a slight stable potential window of aqueous electrolytes. Several other non-aqueous electrolytes that belong to organic class have been studied to boost output operating voltage which usually delivers 2–3 times broader working voltage window as compared to aqueous ones. Hence, the investigation of ECs that are based upon TMO (using organic electrolytes) is of great significance to attain greater energy density that will significantly cover the practical implementation of ECs. Besides the assessment based on electrochemical progress, other concerns about cost, and comfort, protection, and environmental compatibility of production and manipulation must also be engaged into thoughtful concern when TMOs are developing for LIBs to make them industrially applicable. It must be stressed about the synthesis mechanism of these TMO materials as it must be definitely

A complex method is the electrochemical reduction of oxygen over TMO catalysts that can comprise altered mechanisms that can be regulated through the nature of TMOs, owing to their adsorption and physicochemical properties. Till now, limited studies that are mainly attentive to the effect of catalyst features, mechanism, and kinetics of complex method discussed above. Further, adsorbed oxygen on the reaction rate, the intrinsic interactions between TMO catalysts and carbonaceous matrixes are also involved. The only trouble that is associated with examining the electrochemical procedures on TMOs are related to their semiconducting properties. These properties can lead to change in the behaviors of reactions on TMOs catalysts in comparison with the metal-based catalysts. Future progress might lead to extremely effective and inexpensive TMO catalysts after some heightened between the corrosion resistance, electro-catalytic experiment, fabrication

Given the difficulties ahead, there is optimism that TMOs will be the materials forum soon for overcoming many of the existing bottlenecks problems in sustainable and renewable energy storage/conversion sectors. To accomplish this purpose, momentous improvements in electrochemical efficiency and a comprehensive understanding of TMOs dynamics in energy storage/conversion applications must be established. These fascinating TMO materials will provide a new path to make desirable energy innovations that will economically feasible with continued and

*DOI: http://dx.doi.org/10.5772/intechopen.96568*

scalable for commercial applications.

committed research efforts.

**Conflict of interest**

cost, thermodynamic stability, and long-term stability.

Authors have declared no 'conflict of interest.

#### *Rational Design and Advance Applications of Transition Metal Oxides DOI: http://dx.doi.org/10.5772/intechopen.96568*

*Transition Metal Compounds - Synthesis, Properties, and Application*

etc.) has also been characterized and studied [105–107].

*Scheme of photo-induced processes at a TiO2 semiconductor/electrolyte interface [103].*

**5. Outlook, challenges, and a little science fiction**

cal performance to meet today's energy demands.

In biomedical field, magnetic metal oxides have been used with biological agents, have excellent applications. As superparamagnetic Fe3O4 can act as potent nanoprobes magnetic fluid hyperthermia (MFH), biosensors, magnetic resonance imaging (MRI) are biocompatible and stable chemically as well as magnetically. For therapy and targeted drug delivery, Ferrite MFe2O4 (where M = Mn, Zn, Ni, Co,

The synergic effects and complex chemical configurations of several metal species in the TMOs induce noteworthy electrochemical performance. Numerous elegant approaches including compositions and manipulation of the micro/nanostructures have been widely established, that aims to endorse utilization of TMOs in everyday energy conversion technologies and enhancement of electrochemical performance. However, each designed approach applies lonely that normally consequences in partial enhancement in of electrodes based upon TMOs with respect to their electrochemical performance. Thus, it is more fascinating to assimilate manifold stimulating design approaches, therefore aggregating their electrochemi-

The mainstream of research reports owing to the utilization of TMOs related to boost energy storage devices is primarily based on the observations of a specific experiment. A wide-ranging insight into the connection among the composition (structure) and properties of these TMOs that are related to their performance has not been systematically attained yet. Thus, effective and reliable methods and standards are necessary to develop urgently to assess the energy storage devices that are based on TMOs. Theoretical simulation and mathematical modeling are also greatly anticipated to be established in order to direct large-scale, low-cost, and facile fabrication along with the purposeful design of TMOs for greater electrochemical performance.

Realizing the unsuccessful mechanisms upon cycling in the electrodes based upon TMOs for LIBs is crucial to direct the scheme and design of progressive materials. This needs to understand the compositional parameter and structural evolution as well as consideration of electrolyte compatibility matter. The amendment of electrolytes including certain reversible redox-couples (as additives) in aqueous electrolytes has been demonstrated that could considerably progress the general electrochemical progress of pseudo-capacitive materials. Thus, we also assume that appropriate scheme and design of electrolytes could additionally elevate the electrochemical performance of TMOs for both rechargeable batteries. Additionally,

**16**

**4.5 Biomedical**

**Figure 11.**

the assessment of pseudo-capacitive progress of TMOs is generally accomplished in aqueous electrolytes. This accomplishment is unescapably restricts the energy density owing to a slight stable potential window of aqueous electrolytes. Several other non-aqueous electrolytes that belong to organic class have been studied to boost output operating voltage which usually delivers 2–3 times broader working voltage window as compared to aqueous ones. Hence, the investigation of ECs that are based upon TMO (using organic electrolytes) is of great significance to attain greater energy density that will significantly cover the practical implementation of ECs. Besides the assessment based on electrochemical progress, other concerns about cost, and comfort, protection, and environmental compatibility of production and manipulation must also be engaged into thoughtful concern when TMOs are developing for LIBs to make them industrially applicable. It must be stressed about the synthesis mechanism of these TMO materials as it must be definitely scalable for commercial applications.

A complex method is the electrochemical reduction of oxygen over TMO catalysts that can comprise altered mechanisms that can be regulated through the nature of TMOs, owing to their adsorption and physicochemical properties. Till now, limited studies that are mainly attentive to the effect of catalyst features, mechanism, and kinetics of complex method discussed above. Further, adsorbed oxygen on the reaction rate, the intrinsic interactions between TMO catalysts and carbonaceous matrixes are also involved. The only trouble that is associated with examining the electrochemical procedures on TMOs are related to their semiconducting properties. These properties can lead to change in the behaviors of reactions on TMOs catalysts in comparison with the metal-based catalysts. Future progress might lead to extremely effective and inexpensive TMO catalysts after some heightened between the corrosion resistance, electro-catalytic experiment, fabrication cost, thermodynamic stability, and long-term stability.

Given the difficulties ahead, there is optimism that TMOs will be the materials forum soon for overcoming many of the existing bottlenecks problems in sustainable and renewable energy storage/conversion sectors. To accomplish this purpose, momentous improvements in electrochemical efficiency and a comprehensive understanding of TMOs dynamics in energy storage/conversion applications must be established. These fascinating TMO materials will provide a new path to make desirable energy innovations that will economically feasible with continued and committed research efforts.

## **Conflict of interest**

Authors have declared no 'conflict of interest.
