Nancomposites.....!

1.1       Electrochemical cell

The electrical energy produced from chemical energy is known as electrochemical energy. An electrochemical cell converts chemical energy into electrical or may assist chemical reaction to proceed by applying electrical energy. The chemicals in the conducting liquid (the electrolyte) convert into charged particles (ions) when two dissimilar metals are immersed in it. These ions result in the flow of current and the process is termed as electrolysis .

Electrochemical cell involves redox reactions, i.e oxidation and reduction reaction.  In terms of oxygen transfer, oxidation is the gain of oxygen while reduction is the loss of oxygen. In terms of hydrogen transfer, oxidation is the loss of hydrogen whereas reduction is the gain of hydrogen. With regards to transfer of electrons, oxidation is the loss of electron while reduction is the gain of electrons.

1.1.1   Electrodes

There are two electrodes of an electrochemical cell; anode and cathode. Reduction occurs at the cathode while oxidation occurs at the anode. There are basically two types of electrochemical cell:

1. Galvanic cell

2.  Electrolytic cell

 1.1.2     Galvanic cells

Galvanic cell produces electricity by converting chemical energy into electrical whereby the electrons flow from anode to cathode in the external circuit. The redox reaction is spontaneous in this cell. The anode of the galvanic cell is negatively charged while the cathode is positive with the two half cells being placed and set in different containers, connected by a salt bridge or porous partition.

1.1.2.1  Electrolytic cell                                                 

Electrolytic cell involves non spontaneous redox reaction, i.e. we have to provide the electrical energy usually supplied with an external battery, which is converted to chemical energy. The electrodes of the cell are placed in a same container in which a  molten electrolyte solution is also present. The anode is positive while the cathode is negative and the electrons enter through cathode and come out through the anode .

1.2           Nanocomposite

Nanocomposite material has at least one of the three dimensions of each of the constituents (matrix or reinforcement) in nanoscale (100 nm or less). Compared to the bulk composites, the nanocomposite matrix could be :

Ø Metallic

Ø Ceramic

Ø Polymeric

In the same way the reinforcement could be of three types :

·                     Particles:

Silica, nanospheres, organic and inorganic materials, metals, 3–d nanofillers, nanopowders, amorphous and crystalline.

·               Layered materials:

Silicates, graphite other layered minerals, layers typically with thickness of the order of 1 nm but with aspect ratio in other two directions of at least 25.

·                 Fibrous materials: nanofibres and nanotubes etc.

Improvement in the nanocomposite is the result of two principal factors:

1.                  Increased surface area.

2.                  Quantum effects.

Interfacial interaction and quantum effects related to nano scale dimension may also show improvements in some nanocomposite. The multifunctional properties of a nanocomposite may be completely different from their bulk counterparts.

1.3           Cermet

            In metallurgy materials made up of metal and ceramics are generally referred to as Cermets. In cermets, the metal phase acts as matrix with ceramic particles disseminated through it. They are also called as cermat or ceramal. Cermets are highly durable, heat-resistant alloy formed by compacting and sintering a metal and a ceramic substance.

Important properties of cermets are as follows:

a.                   Durablility

b.                  Resistant to oxidation and high temperatures

c.                   Toughness (property derived from metals)

d.                  Impact strength

1.3.1         Application of cermets

          

           Electrical components which get extremely hot during operation, they need to behave like ceramics along with ability to conduct electricity, like metals. Cermets are perfect solution in components such as resistors and vacuum tubes (valves).

1.4           Fuel Cell  

Fuel cell is an electrochemical device that converts chemical energy to electrical energy. Fuel Cell was discovered by William Robert Grove with Charles Langer and Ludwig Mond [6] in 1839 making their first practical fuel cell device using air and coal gas in 1889. NASA made the first ever commercial use of fuel cell for power generation . Hyundai most recently has handed over the first hydrogen fuel cell based car keys to their first customer .

Fuel cell consists of an anode where the fuel undergoes a chemical reaction producing free electrons and ions. The ions flow from anode to cathode via an electrolyte and the electron travel through the external circuit and are collected at the cathode generating electric current. Eventually the ions, electrons and oxygen combine to produce water as a by product. There are broadly five different types of fuel cells  namely, molten carbonate, solid oxide, phosphoric acid, polymer membrane (PEM) and alkali. However, the focus of a large number of researchers was on solid oxide fuel cell (SOFC) because this type of fuel cell offers better electronic and ionic conductivity at high temperature compared to the others. Also, it avoids the use of precious metals like platinum as a catalyst and improves the efficiency of the fuel cell up to 80%-85% by capturing and reusing the waste heat .

Despite several excellent advantages, there are many drawbacks of conventional power generation systems such as poor conversion efficiency and emission of environment pollutants. Further conventional high operating temperature demands material compatibility challenges and high costs as well. An alternative to the conventional technologies, fuel cell is an efficient and flexible electrochemical device nowadays referred to as future energy converting devices that directly converts chemical energy into electrical energy. Batteries are secondary storage devices while fuel cells are primary sources of energy generation. An extraordinary advantage of fuel cell is that it converts energy from one form to another just in one step compared to the multi step processes involved in other combustion based heat engines, including energy conversion from chemical to thermal to mechanical and then finally to electrical .

Fuel cell technology further aids in the production of energy in a process that is not detrimental to the environment compared to the present technologies that cause severe damage to our environment by changing climate of regions, causing acid rains and most importantly ozone layer deposition. Compared to engines and modern thermal power plants (30%), fuel cell technology offers high efficiency (up to 85% energy efficiency when combined with gas turbine .

Fuel cell technology aims to be compatible with renewable sources and modern energy carriers with wide range of fuels which can be used directly. Including hydrogen, natural gas, coal gas, reformed gasoline or diesel and gasified carbonaceous solids (e.g. municipal solid waste and biomass . The static nature of fuel cells also means quiet operation without noise or vibration, while their inherent modularity allows for simple construction and a diverse range of applications in portable, stationary, and transportation power generation