**Abstract**

Apart from the magnetic properties, ferrites have been considered as efficient electrodes for next generation energy storage devices. This chapter will include applications of spinel ferrites such as MnFe2O4, CoFe2O4, ZnFe2O4 and NiFe2O4 in supercapacitor. In ferrites, the charge storage arises from the fast-reversible surface redox reactions at the electrode/electrolyte interface. In particular, the electrode material with high specific capacitance, wide range of operating potential, low synthesis cost and its availability on the earth are highly desirable to fabricate a supercapacitor. Ferrites with mixed oxidation states have proved as promising electrodes in supercapacitors. In this chapter, we summarize the different synthesis methods of ferrites based nanocomposites and their electrochemical properties for supercapacitor application.

**Keywords:** ferrites, nanocomposites, electrochemical properties, electrodes, supercapacitor

## **1. Introduction**

The continuous depletion and consequently the increased cost of the fossil fuel has now become an economic problem for a nation. Moreover, the production of CO2 from massive use of fossil fuel in transportation and industrial operations increases the greenhouse gases which are responsible for significance change in climate (global warming). In future, the demand of fossil fuel is expected to be increased rapidly. Therefore, some alternative energy storage systems need to be developed in order to meet the demand of energy consumption. Battery is being widely utilized in electric vehicles and electronic devices because of its large energy density [1–4]. However, the maintenance at regular interval and low power density are some drawbacks with battery.

Among various energy storage devices, supercapacitor technology has attracted tremendous attention to be used in high power application because of their higher power density and longer cycling life [5–9]. **Figure 1** depicts the power density and energy density of capacitor, battery and supercapacitor. The capacitor with largest power density occupies the top position, however, the energy density is much lower. Battery can exhibit larger energy density but with lower power density. The supercapacitors occupy the important space between capacitor and battery with larger power density than batteries and greater energy density than capacitors. Supercapacitors are considered suitable candidates as energy storage in portable consumer electronic devices, memory back-up systems, microelectromechanical systems, hybrid electric vehicles and medical devices [10–17]. Further

#### **Figure 1.**

*Ragone plot for various charge storage devices. Supercapacitors occupy the space between capacitors and batteries with larger energy density than capacitors and larger power density than batteries.*

improvements are being made in order to extend the applications of supercapacitor in different purpose [18–20]. Due to a simple structure (similar electrodes), supercapacitor technology can be integrated on a Si chip with energy harvesters [21–23].

Supercapacitor can store an excess energy from the harvester and return back when required. The supercapacitor performance is governed by the electrodes, current collectors, separator and electrolyte. The surface morphology and electrical properties of electrodes are the major factors which mainly control the energy storage in supercapacitor. In this connection, a lot of efforts are being made towards developing new materials for electrodes and improving their electrochemical properties [24–29]. Many materials and their composites have been explored as electrodes for supercapacitor [30, 31].

Supercapacitor electrodes can be categorized in two types, 1) Metal oxides, which involve faradaic process to store the charge (Pseudocapacitor) [32–34], 2) carbon and silicon based materials, these materials store the charge in electric double layer (EDL) [27, 35–37]. EDLCs exhibit high rate capability and longer cycle life, but low energy storage capacity is a major issue for them [38–40]. On the other hand, metal oxide based supercapacitor exhibits larger capacitance and energy density than EDLC but the poor rate capability and limited charging/discharging cycle numbers are some of their drawbacks [7, 15, 41]. To design a supercapacitor with larger energy density without compromising the rate capability is a major challenge. In this context, several electrode materials and their combinations have been evaluated for high performance supercapacitor [5, 42–44]. The ferrite materials are also being considered as potential electrodes in supercapacitor because of their different oxidation states, low price, environmental benignity, and their large abundance [26, 45–49]. Moreover, their synthesis process is simple and suitable for production at industrial scale. MFe2O4 (M = Mn, Co, Ni, Zn, or Mg) ferrites have been extensively used in supercapacitor. These binary oxides can offer large capacitance due to involvement of two ions in redox reactions [13, 47, 50]. Subsequently, several studies were performed on ferrite materials such as nickel ferrite, bismuth ferrite, cobalt ferrite, manganese ferrite, as electrodes in supercapacitor [46, 51–53]. Ferrites of the form MFe2O4 (M = Ni, Co, Zn, etc.) have been considered as potential electrodes in energy storage devices because of their good chemically stability and electronic properties. Moreover, their nanocomposite can be synthesized using water based solution without any organic solvent (**Figure 2**). In this chapter, research progress

*Application of Ferrites as Electrodes for Supercapacitor DOI: http://dx.doi.org/10.5772/intechopen.99381*

#### **Figure 2.**

*Synthesis of ferrite (bismuth ferrite)–graphene nanocomposite as electrodes for supercapacitor using water based solution [34]. Bismuth ferrite and graphene were mixed in DI water and then deposited on a conducting substrate by drop casting process to fabricate the electrodes for supercapacitor.*

on ferrite based electrodes (MFe2O4 types) for supercapacitor have been summarized. The supercapacitor performance of ferrite depends on their morphology, synthesis process, used precursors, and composition.
