Here we will discuss Hybrid Super Capacitor: Electrode Material for Super Capacitor
Carbon materials, Activated carbon, Carbon nanotubes, Graphene, Metal Oxides
Hybrid Super Capacitor:
Hybrid supercapacitor was devolved by combining the
characteristics electric double layered capacitor and pseudocapaictors. This
capacitor is more advance than later both capacitors because its half part act
as pseudocapaictors and half act as electric double layered capacitor.
Hybrid supercapacitor has high energy density, long cycle
lifetimes, high power delivery and good energy storage capacity. Supercapacitor
has lot of application in different fields of life like automobiles, buses,
trains, crane and elevators (Conway, 2013).
In hybrid Supercapacitors no metal oxides are used like in
batteries therefore no chance of explosion or fire. Hybrid Supercapacitors are
considered safe, reliable and most efficient than other energy storage devices.
Hybrid Supercapacitors has power distribution and improves the reliability
which makes it most superb energy storage device (Kim, Sy, Yu, & Zhang,
2015).
Electrode Material for Super Capacitor:
All components of supercapacitor are most important but
electrode materials are most important because most of research have been doing
on supercapacitor materials. Electrode materials play a key role for
supercapacitor performance.
Different materials was used as an electrodes such as
conducting polymers due to lot of productions, carbon based materials,
different metal oxide and their derivatives. These materials give many
important and tremendous results but also show many draw backs (Hao Yang et
al., 2017).
Carbon Materials:
Carbon based materials got more attention of researcher because
it provide continuously energy. Due to its uninterruptable power supply it’s
mostly used in airplanes, laser and portable electronic devices. Another
important characteristic of carbon is its abundance availability on earth crust
also exists in allotropic forms of graphite and diamonds and lot of application
in daily life materials (Bo et al., 2012).
Activated Carbon:
Activated carbon widely used as an electrode material due to
unique characteristics large surface area, moderate cost and good electrical
conductivity. The term "activated carbon," commonly referred to as
"activated charcoal," refers to a type of carbon that has undergone
processing to increase its surface area and porosity, making it a powerful
adsorbent substance.
It is created by heating carbonaceous materials, such as
coconut shells, coal, or wood, in the presence of a gas that does not react
with the carbon. (Bo et al., 2012).
Researcher reached at result that there is wide gap between
specific surface area and specific capacitance. This shows all pores of carbon
are not activated for charge accommodation because specific surface area is
approximately 3000 m^2/g and give small specific capacitance. These problems
lead to loss of power capability and low energy density. It is also observed
that capacitance of activated carbon for organic electrolyte is less than
aqueous electrolyte (Pandolfo & Hollenkamp, 2006).
Carbon Nanotubes:
Carbon nanotube used as electrode materials in
supercapacitor gets great attention due to its superb mechanical and thermal
conductivity, pore structure and unique electrical properties. Carbon nanotubes
used in electronic circuits, solar cells, batteries, thermal detectors for
laser and Supercapacitors.
Carbon atoms are organized in a specific crystalline structure
to form cylinder-shaped carbon nanotubes (CNTs). With lengths up to several
millimeters and diameters as small as a few nanometers, they have a high aspect
ratio. Depending on how many layers of carbon atoms make up the tube, CNTs can
either be single-walled or multi-walled. (Yakobson & Avouris, 2001).
CNTs are used in such applications due to their unique pore
structure, highly accessible surface area, low electrical resistivity, variety
of redox reactions and high chemical stability (Cheng et al., 2011).
Graphene:
Graphene get high attention due thick layer two dimensions
(2D) structure and unique material that has high potential to use for energy
storage device because of its good characteristics. A single layer of carbon
atoms organized in a hexagonal lattice make up the two-dimensional substance
known as graphene.
With a thickness of just one atom, it is the thinnest
material known and possesses special electrical, thermal, and mechanical
properties that make it a potential material for a variety of applications
(Marcano et al., 2010).
Recently it was proposed that graphene is very important for
supercapacitor as electrodes materials because it does not depends on
distribution of pores at solid state as like other materials like carbon tubes,
activated carbon (C. Liu, Yu, Neff, Zhamu, & Jang, 2010).
Metal Oxides:
Metal oxide mostly used in supercapacitor due to its high
electrical conductivity low resistivity and simpler structure Compounds called
metal oxides are made of a metal element and oxygen. They are some of the most
prevalent substances in the crust of the Earth and are extensively utilized in
both industry and technology. (Hualan Wang, Hao, Yang, Lu, & Wang, 2010).
Many oxides are used as electrodes materials in
Supercapacitors but most important examples are manganese oxide (MnO2) nickel
oxide (NiO) iridium oxide (IrO2) and ruthenium oxide (RuO2). Metal oxide are
most important because low cost and easily available.
Depending on the particular metal and the oxidation state,
metal oxides have a variety of physical and chemical characteristics. They can
be applied to many different things, including catalysts, semiconductors, and
magnetic materials. The use of metal oxides in energy conversion and storing
devices like solar cells and batteries is also being investigated. (Iro,
Subramani, & Dash, 2016).
Carbon materials are low cost, high stability at different
temperature, high conductivity and show long cyclic life, large surface area.
(Namisnyk, 2003).The most important example of carbon materials are carbon
aerogel, activated carbon, carbon nanotubes, graphene etc. (Ao, Kocher, &
Choct, 2012).
