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UNIT III: ENERGY SOURCES
Session : 19 Topic : Nuclear energy- Nuclear energy-differences between nuclear reaction &
chemical reaction –Nuclear fission & fusion reactions with examples – Chain reactions
INDRODUCTION:
 The nucleus is the central part of atom of any element and it is composed of protons and
neutrons. These particles – protons and neutrons are collectively termed as nucleons. Protons
carry unit positive charge and unit mass. Neutrons carry no charge but unit mass.
 Number of elements such as uranium and radium are unstable .Their atomic nucleus
breaks of its own accord to form smaller atomic nucleus of another element. Nucleons in the
unstable nucleus regroup to give new nucleus. This causes the release of excess particles and
energy from the nucleus called radiation. The spontaneous break down of unstable atoms is
termed radioactive disintegration or radioactive decay.
 Types of radiation:
α-particles: helium nuclei represented as 2H4 emitted from radioactive nuclei
β-particles: are identical with electrons symbolized as -1β0 or -1e0
γ-particles: electromagnetic radiation of shorter wavelength represented as 0γ0
 Nuclear reactions are the processes associated with change in their nuclei content,
resulting in the change in composition of the nucleons , unlike chemical reactions nuclear
reactions are associated with higher magnitude of energy content (Mega Joules – MJ or mega
electron volt - MeV), compared to chemical reactions (Kilo Joules – KJ).
 Differences between nuclear and chemical reactions
1. Rearrangement or redistribution of nuclear particles, whereas there is redistribution of
valence electrons in chemical reactions.
2. One element to another element; whereas reactants converted to products in chemical
reactions
3. Release or absorption of enormous energy when compared to chemical reactions.
4. Nuclear Reactions unaffected by external factors (conc., temp, pressure and catalyst).
NUCLEAR FISSION:
 Nuclear fission process is the splitting of heavy nucleus into two or more smaller nuclei
with liberation of large amount of energy.
 Nuclear fission can be made by bombarding an atom by alpha particles, neutron,
deuteron etc. But bombardment by neutron results in a sustained chain reaction.
 Example for fission: bombardment of uranium by neutrons .
U235 +
n1 → 56Ba137 + 36Kr97 + 0n1 + 193.6 MeV
(fast or slow)
 Salient features of nuclear fission process are:
1 It is associated with emissions of neutrons 2.the products of fission called as “fission
fragments” are also radioactive. These fragments decay to stable nuclei by a series of βemissions. 3.Nuclear fission is a self-propagating chain reaction, as the emitted neutrons can
cause further fission reactions in other nuclei. Hence the emitted, energetic neutrons are
92
0
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called secondary neutrons. The process of production of secondary neutron sustains the chain
reaction.
 Nuclear fission can be brought by neutrons of high, moderate or low energy . Isotopes
such as U235, Pu239 and U233 are fissionable (can be split into lighter nuclei) by neutrons of any
energy content but the isotopes U238, Th232 and Pu240 are fissionable only by high-energy
neutrons are called fertile materials.
 Neutrons are “thermal” and “fast” neutrons based on their energy content. Thermal
neutrons are those with the energy content of 0.025 eV. Fast neutrons are those possessing the
energy content of few million electron volts.
CHAIN REACTION:
 It is a continuous process in which one or more of the products themselves trigger(s) the
reactions to take place non-stop. Each fission reaction of U235 nucleus results in large amount
of energy and is also accompanied by the release of 2-3 (2.5) neutrons on an average. These
neutrons act as chain carriers (trigger further reactions) and thus become capable of bringing
about a sustained chain reaction. If this fission (chain) reaction proceeds uninterrupted, very
huge amount of energy is released (instantaneously) within the fraction of a second, leading
to nuclear explosion. If the chain reaction is controlled, it can be used to produce power in a
device called nuclear reactor.
 Condition for maintaining a sustained chain reaction is to have a sufficient concentration
of U235 or Pu239 or any other enriched nuclear fuel to provide a good neutron flux. Otherwise
the development of the sustained chain reaction may be hindered due to the loss of neutrons
(chain carriers) caused by their escape from the active material lump or by their absorption to
cadmium control rods.
 Critical Mass:
The minimum mass of nuclear material required to initiate the chain
reaction is called “critical mass”. The critical mass of a nuclear fuel is inversely related to the
percentage of fissile (fissionable) material in the fuel. Natural uranium contain 99.3% of
U238and 0.7% of U235
 Multiplication factor: Nuclear chain reaction is controlled in such a way that an average
of one neutron created in a fission process is capable of activating another nucleus to cause
fission. This condition is defined by multiplication factor K.K is the ratio of the number of
neutrons produced by fission in any one generation to the number of neutrons produced in
the immediately preceding generation. If K > 1 No. of fission events increases for each
successive neutron generation. K= 1 No. of fission per unit time is constant. K< 1 chain
reaction cannot be maintained.
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NUCLEAR ENERGY – MASS DEFECT (ΔM) AND BINDING ENERGY (ΔE):
 The mass of an atomic nucleus is actually less than the sum of the masses of the
constituent nucleons. This difference in mass (sum of the masses of the constituent nucleons
minus the actual mass of nucleus) is called mass defect. The energy equivalent of the mass
defect, as per the Einstein’s mass-energy equivalence, is called binding energy. Binding
energy can be alternatively defined as the energy released when the required number of
protons and neutrons coalesce to form the nucleus or the energy required to disrupt the
nucleus into the constituent nucleons (protons and neutrons). Binding energy (B.E.) is
expressed in terms of mega electron volts (MeV). 1 MeV = 1.602 X 10-13 Joule
 Einstein’s law can be written for binding energy as ΔE = (Δm)C 2 where B.E., Δm and C
are respectively the binding energy, mass defect and velocity of light. Binding energy values
of nuclei increase progressively as the mass numbers of the elements and this rate of increase
is less at higher mass numbers.
 Consider the formation of helium nucleus. The most abundant isotope of helium 2He4,
contains 2 protons and 2 neutrons in the nucleus and 2 electrons outside the nucleus. In other
words, it is formed by the combination of two hydrogen atoms (i.e., 2 protons and 2
electrons) and tow neutrons. Its atomic mass (M’) should be given by
M’
=
=
=
2mH + 2mn
2 x 1.007825 + 2 x 1.008665
4.03298 a.m.u.
Actual mass of helium atom (M) on the same scale is 4.00260 a.m.u.
Mass defect, ∆M = M’ – M = 4.03298 – 4.00260 = 0.03038 a.m.u.
Energy released in the formation of helium nucleus = 0.03038 x 931.5 MeV.
Thus an enormous amount of energy is released by the formation of a nucleus from those of
lighter elements on account of the mass defect.
NUCLEAR FUSION REACTIONS:
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 The formation of a heavier nucleus, as of helium from those of lighter elements, as of
hydrogen, is known as nuclear fusion.
 Nuclear fusion can also take place by allowing highly accelerated protons and deutrons,
etc., to fall on nuclei of lighter elements. Such processes, however, occur at reasonable rates
only at very high temperatures of the order of a million degree centigrade, which exist only
in the interior of stars. Such processes are, therefore, called thermonuclear reactions. Once a
fusion reaction is initiated, the energy released is sufficient to maintain the temperature and
to keep the process going.
 The energy of the sun is supposed to arise from the following thermo-nuclear reactions:
(i) 1H1
(ii) 1H2
(iii) 2He3 +
0
H1 → 1H2
+
+
1e
(Deuteron) (positron)
1
3
+
+
Energy
1H → 2He
Isotope of helium
3
4
+
21H1 +
2He →
2He
(Helium)
+
1
Energy
Energy
The overall reaction, therefore, may be written as
 The formation of 1 mole of 2He4 from four moles of hydrogen releases 27.30 x 10 8 kJ of
energy.
Difference between Nuclear Fission and Nuclear fusion
Nuclear Fission
Nuclear Fusion
1. It is process of breaking a heavy nucleus with
some projectiles into two or more light fragments,
with liberation of a large amount of energy.
2. This process results in the emission of radioactive
rays.
3. This process takes place spontaneously at
ordinary temperature.
4. The mass number and atomic number of the
daughter elements are considerably lower than that
of the parent nucleus.
5. This process gives rise to chain reaction
6. During nuclear fission, neutrons are emitted.
7. Nuclear fission can be performed under
controlled conditions.
It is process of fusionof two light nuclei into a
single nucleus, with the liberation of a large amount
of energy.
This process does not emit and kind of radioactive
rays.
This process takes place at very high temperature.
The mass number and atomic number of the product
is higher than that of the starting elements.
This process does not rise to chain reaction.
During nuclear fusion, positrons are emitted.
Nuclear fusion cannot be performed under
controlled conditions.
Session :20 Topic: Light water nuclear power reactor- principle-components with examples &
functions
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Light Water Nuclear Reactor (Power Plant):
 A nuclear reactor or a pile is device for carrying out fission reaction in a controlled rate
so that the liberated energy can be utilized for peaceful purpose.
 The main components of a typical nuclear reactor are (i) reactor core (ii) reflector (iii)
pressure vessel
(iv) structural materials and (v) shielding unit.
 Principle: The core of the nuclear reactor consists of fuel elements, moderators, coolants
and control rods. In a nuclear reactor, heat generated by the controlled fission chain reaction
of the nuclear fuel is transferred to the coolant and this heat (transferred to the coolant) is
used to generate high-pressure steam. The generated high-pressure steam triggers a turbine
connected to the generator, thus producing power.
 Reactor core is the principal component of any nuclear reactor. The fissionable fuel
material is packed in this unit and heat is liberated due to fission. It consists of fuel elements,
moderators, coolants and control rods. The fuel element has a pack of material containing
fissile isotope, termed as nuclear fuel. E.g. U235, U233, Pu239 . Fuel elements used in nuclear
reactors are made of metal or alloy example uranium, uranium oxide (UO 2) or uranium
carbide (UC or UC2).
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 The moderator material serves to reduce rapidly (within faction of a second) the high
energy of the fission neutrons. The requisites of a good moderator are (i) it should have high
slow down process i.e. reduce the energy of fast neutrons from 1-2 MeV to 0.025 MeV (this
property is possessed by elements with low mass numbers) (ii) it should have low cross
sectional area for neutron absorption and larger areas for neutron scattering (iii) it should be
cheap / abundant in pure form (iv) it should possess good stability to chemicals, heat and
radiations and (v) it should possess good corrosion resistance and high melting point for solid
materials. Examples of moderator materials : water, heavy water (D 2O), graphite, beryllium,
organic compounds etc. heavy water is the best moderator. Natural water contains 0.015 % of
D2O.
 Coolants the requisites of coolant material used in nuclear reactors are (i) high heat
capacity (ii) high thermal conductivity (iii) stability to heat and radiation (iv) low cross
sectional area for neutron absorption (v) cheapness and low power requirement for pumping
(vi) non-corrosive and non-toxic nature and (vii) high boiling point and low melting point.
Coolants used in nuclear reactor are water, heavy water, liquids, organics and gases.
 Control rods function to control the neutron flux. The materials used as control rods are
boron, Steels with boron content, boron carbide (B4C), boral (B4C dispersed in Al) etc.
10
+ 0n1 → 5B11 + γ ray
5B
 Reflector reflects back many neutrons, which leak out from the core of the nuclear reactor.
The reflector material enables to decrease the critical mass (minimum mass of fissile material
required to sustain the chain reaction, after initiation) and to increase the average power
output for a given amount of fuel. Moderators such as heavy water, graphite, beryllium or
water are used as reflector in thermal reactors.
 Pressure vessel is used to enclose / encapsulate the core of the nuclear reactor and
reflector and withstand high pressures of the order of 200 kg/cm
 Shielding is the process of attenuation of γ-rays and neutrons emerging from the nuclear
reactor. It enables the protection of operating personnel from radiation hazards. Shielding
process may be effected by (i) thermal or (ii) biological methods.
(i) Thermal shields are provided close to the core of the reactor, covering few inches’ thick
layer of iron or steel. Thermal shielding absorbs γ-rays and protects bio-shields from
overheating. Thermal shield is located such that it is readily cooled by the circulation of
water.
(ii) Bio-shielding unit comprises a thick layer (several feet thick) of concrete, which
surrounds the core, reflector and thermal-shielding units of the nuclear reactor. All the above
mentioned components of the nuclear reactor are enclosed in steel containers.
 Most of the commercial power plants are light water plants. In which U 235 fuel rods
submerged in water. Here water act as coolant and moderator. B 10 is used as control rods.
Session :21: Topic : Breeder reactor and wind energy
BREEDER REACTOR OR REGENERATIVE REACTORS OR CONVERTERS:
 A nuclear reactor can be designed in such a way that it can generate its own fuel by
converting the fertile material(U238,Th232 )into fissile material.( Pu 239, U233) or produces more
fuel than it consumes. The fast reactor is used for power production and more importantly for
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producing or breeding fissile material. The large proportion of fertile U-238 present in the
fuel captures neutron to undergo successive β-emissions to give Np-239 and Pu-239. Pu-239
is fissionable by thermal neutrons and yields about 3 neutrons per fission.
 Since a fertile material (U-238) is converted into a fissile material or secondary fuel (Pu239) the reactor is called converters or regenerative reactors
 Conversion factor(Defined as the ratio of no of secondary fuel atoms produced to the
no.of primary fuel atoms consumed.) for Breeder reactor it is > 1
WIND ENERGY:
1.
2.
3.
4.
 Like solar power, wind has propelled ships as well as driven wind mills used to grind
grain and pump water. Winds are caused from two main factors: 1) Heating and cooling of
the atmosphere which generates convection currents. Heating is caused by the absorption of
solar energy on the earth’s surface and in the atmosphere.2)The rotation of the earth with
respect to atmosphere, and its motion around the sun.
 The potential of wind energy as a source of power is large. Wind, which is essentially air
in motion, has kinetic energy by virtue of the movement of large masses of air caused by
differential heating of the atmosphere by the sun. The energy available in the winds over the
earth’s surface is estimated to be 1.6 x 107 MW. This energy can be utilized for performing
mechanical and electrical works. Wind turbines can be used to generate electricity, for lifting
water from wells, for direct water pumping and many more. Wind turbine, basically, consists
of a few vanes or blades radiating from a central axis. As the wind blows against the
vanes/blades, they rotate about the axis. This rotational motion is then utilized to perform
some useful work-mechanical and / or electrical.
 Types of wind mills: 1.Multiblade type wind mill 2. Sail type wind mill 3. Propeller type
wind mill Savonius type wind mill 5. Darrieus type wind mil
 Advantages of wind mills:
It is a non-polluting and environment friendly source of energy.
It is an important renewable and sustainable source of energy, available free of cost.
The generation period is low and power generation starts from commissioning.Power
generation is cheaper as there is no shortage of input cost and recurring expenses are almost
nil
It can be made available easily in many off-shore, on-shore and remote areas; thus, helpful in
supplying electric power to remote and rural areas.
Limitations:
It has low energy density.
It is variable, unsteady, irregular, intermittent, erratic and sometimes dangerous.
It is generally, favourable in geographic locations which are away from cities.
Wind turbine design, manufacture and installation have proved to be complex due to
widely varying atmospheric conditions in which they have to operate.
5. The use of wind power for generation of electricity on a large scale is not econ

1.
2.
3.
4.
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Session :22: Topic : Solar energy conversion and solar cells-principle & applications.
 Sun is the ultimate source of energy. The thermonuclear fusion taking place in the sun
releases enormous quantity of energy in the form of heat and light.
 The direct absorbtion of solar energy and its conversion into more useful forms can
occur through either by thermal conversion or by photo conversion.
 Thermal Conversion involves absorbing the thermal energy in the form of infrared
radiation.
1 .Solar Cookers: It uses the heat of the sun by reflecting the solar radiation using a mirror
directly on to a glass sheet kept over blackened boxes. Food can be cooked by keeping it in
these blackened boxes.
2. Solar Water heaters: It consists of an insulated box of which is painted with black paint. It
also contain glass lid which is used to receive and store solar heat. The black painted coil is
present inside the box is allowed to flow in the cold water which gets heated up and flows
into a storage tank.
Principles and applications of Solar Cells:
 Sunlight can be used to absorb and excite the electrons in the absorbing material .The
excitation in the may be used in a photo electric process to convert light energy into electrical
energy. Photovoltaic cell is a device that converts the incident light energy into electrical
energy. Solar cells work on the principle of photovoltaic cells
 solar cell, without any moving / sliding part in it, converts light energy (of the sun)
directly into electric energy. Hence there is no wear and tear / deterioration of the solar cell
with time, leading to the larger life of the solar cell (20 years or so)
 Semiconductors are used as source materials for making solar cells. They are grown in
such a way that one region is ‘n type’ and the adjacent region is ‘p type’. Holes are the
charge carriers in “p type semiconductors” and ‘electrons’ are the charge carriers in “p type
semiconductors”. A p-n junction is the joining of / bonding between the p and n type regions
within a single crystal. In the absence of external voltage, holes from the ‘p side and
conducting electrons are confined in P and N side respectively.
 When light falls on p-n junction, electrons from the valence bond are promoted to the
conduction band, thereby creating electron-hole pairs on both sides of the junction i.e.
electron-hole bond is dissociated into an electron and a hole. Since the p-n junction is the
barrier to both the types of charge carriers, hole concentration builds up in ‘p side’ and
electron concentration builds up in ‘n side’ of the junction. When these concentrations exceed
the equilibrium concentration of the charge carriers in the corresponding parts of the
semiconductor, drift of holes takes place towards the point A in the diagram with a drift of
electrons towards the point B in the diagram. If A and B are connected across load, electrons
flow from B to A with the current flow from A to B. (It is to be noted here that current
direction is opposite to that of electron flow.) As light falls on the p-n junction continuously,
recombination of electrons with holes ensures uninterrupted electron flow / current.
 Applications: Solar cells made of silicon are used as power sources for spacecrafts /
satellites. . Also, part of electrical energy derived from solar energy by the solar cells is used
for charging the Ni / Cd or Pb / acid (rechargeable) batteries. This electrical energy can also
DEPT.OF APPLIED CHEMISTRY/SVCE
be used to produce hydrogen by the electrolysis of water. Hydrogen thus produced can also
be used in hydrogen-oxygen fuel cell. (Fuel cell is a device that converts fuel energy into
electrical energy.) The limitation of a solar cell is its high cost. A solar cell of 5 cm diameter
exposed to full sunlight can power a standard flash light cell. Conversion efficiency of solar
cell is 10 – 20 %. Research is going on solar cells (i) to cut the cost by 50% and in rural
electrification. Solar-powered air-conditioners are used in Japan. Solar-powered vehicles and
the concept of solar pond for electric vehicle propulsion are also under development.
Session :23 :Topic: Batteries-definition, characteristics, types-alkaline batteries
BATTERIES
INTRODUCTION:
 A cell is a device, which converts chemical energy into electrical energy and vice versa.
Galvanic cell is a device that produces electrical energy from chemical energy and
electrolytic cells convert electrical energy to chemical energy.
 Battery is an array of cells connected in series and / or parallel to produce the desired
voltage / current output. A cell is made up of two electrodes, termed as anode and
cathode. Each cell / electrode is associated with some charge transfer process called cell /
electrode reaction.
 Batteries are of two types namely primary or non-rechargeable and secondary or
rechargeable batteries. The cell reactions for secondary batteries are somewhat reversible
in nature while that of a primary battery is irreversible. Every battery system is
characteristic of its anode and cathode active materials.
 In secondary batteries, the cell reaction can be made to proceed in either direction by
withdrawing or supplying current to the battery system. The current withdrawing process
constitutes the discharging process and the current supplying process, as charging
process. Three important types of secondary batteries (or accumulators) are (i) lead-acid
batteries (ii) alkaline storage batteries and (iii) other batteries including lithium batteries.
 Characteristics of a Battery:
a. Voltage of a battery depends upon the EMF of the cells (E0cell)given by Nernst’s
equation.
b. Temperature increase causes decrease in the value of Ecell and vice versa
c. Current is the rate at which the battery is discharging. A battery can deliver high
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current only if there is rapid electron transfer reaction.
d. Capacity is the amount of electricity that may be obtained from a given battery.
ALKALINE BATTERY:
 Alkaline batteries are improved form of dry cell. In this battery, zinc in powdered form is
mixed with KOH to get a gel. Graphite rod is surrounded by a paste containing MnO 2.
The outside body is made of zinc. The cell reactions are:
Anode:
Zn(s) + 2OH- (aq)
Zn(OH)2(s) +
2 e-
Cathode: 2 MnO2(s) + H2O(l) + 2 eMn2O3 (s) + 2OH- (aq)
--------------------------------------------------------------------------- ------------------------Net reaction: Zn(s) + 2 MnO2 (s) + H2O(l)
Zn(OH)2 (s) + Mn2O3(s)
----------------------------------------------------------------------------------------------------- Advantages of alkaline battery over dry battery are :
(1) zinc does not dissolve as readily in a basic medium
(2) the alkaline battery maintains better its voltage as the current is drawn from it
(3) the life a alkaline battery is longer than dry cell, since there is no corrosion of Zn.
 Uses: Alkaline batteries find used in camera exposure controls, calculators, watches etc.
Session :24 :Topic: Lead acid battery-discharging and charging process
Lead-Acid Battery
Lead-Acid Battery uses lead electrodes and sulphuric acid electrolyte. It consists of a grid
of lead-antimony alloy coated with lead dioxide (used as positive terminal or cathode) and
spongy lead (used as negative terminal or anode). (It should be noted that anode is the electrode
where oxidation of a species takes place; oxidation is loss of electrons by a species and the lost
electrons render the anode as negative pole or terminal. This concept can also be extended to
cathode, being positive.)
The electrolyte is 20 % H2SO4 (with specific gravity γ = 1.15 at 25°C) with number of
electrode pairs containing inert porous partition (called separator). The electrode reactions during
discharging process are as follows:The cell can be represented as
Anod Pb → Pb2+ + 2 ePb2+ + SO42 - → PbSO4
------------------------------Pb + SO42- → PbSO4
-------------------------------
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Cathode PbO2 + 4 H+ + 2e- → Pb2+ + 2 H2O
Pb2+ + SO42- → PbSO4
--------------------------------------------------------------PbO2 + 4 H+ + SO42- + 2e- → PbSO4 + 2 H2O
Overall cell reaction:
+
2-
PbO2 + Pb + 4 H + SO4
Dch
+ 2e --------- → 2 PbSO4 + 2 H2O
←---------ch
During discharge process, lead sulphate is precipitated near cathode and anode and equivalent
amount of water is formed. Thus as the cell supplies electric current, the concentration of
sulphuric acid decreases. But during charging process, sulphuric acid (4 H ++SO42- = 2 H2SO4) is
generated and equivalent amount of water consumed, thereby restoring the original strength of
H2SO4. As both these (charge / discharge) processes are associated with variations in specific
gravity of the acid, the extent of discharging / charging of the cell at a particular time can be
determined by testing the specific gravity of the acid. The cell voltage is in the range 1.88 – 2.15
V as the sulphuric acid concentration is in the range 5 – 40 %.
Uses: 1. SLI (Starting, lighting and ignition purposes) battery 2. Potable power source for
remote areas, mountain regions etc. 3. Standby power source / Uninterrupted Power Supply
(UPS).
Session :25 :Topic: Ni-Cd battery, lithium batteries-reactions and uses
 Secondary
Alkaline
storage
batteries: These
batteries use 20-25 %
KOH
as
electrolyte. Examples of
this type
of batteries are
nickeliron (Edison
cells),
nickelcadmium,
nickel-hydrogen,
nickel-metal
hydride, silver-zinc
etc.
 Nickelcadmium(Nicad )battery
is a example for rechargeable alkaline battery. They find several applications as they are
more versatile than lead-acid batteries in various aspects. During charging and
discharging ,no loss of products and no gas evolution occur at the active electrodes. They
posses low internal resistance ,long shelf life without and good cycle life.
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 Construction :
Anode: cadmium as a mixture of metal oxide and /or hydroxide
Cathode: Nickel(III) oxide hydroxide (NiO(OH))
Electrolyte: KOH
 Cell Reaction:
Overall reaction:
The reaction can be readily reversed , because the reaction products adhere to the
electrode surfaces
 Cell representation:
Cd / Cd (OH)2 // KOH / NiO(OH) / Ni
 Cell Voltage:1.4 V
 Advantages and uses:
a) This battery is widely used in the sealed version for high current applications such as
power tools and applications requiring high cycle life, such as computer power
supply.
b) Large, sealed Ni / Cd cells are used in space applications, which require excellent
system reliability and high cycle life.
c)
Ni / Cd cell can be manufactured in two versions (i) sintered cell and (ii) pocket
cell. Sintered Ni / Cd cells are used for standby power and for starting aircrafts.
Pocket type Ni / Cd cells are used for starting diesel engines and for emergency
lighting.
d) Ni / Cd batteries are costlier than Pb / acid batteries but possess excellent
performance reliability.
LITHIUM BATTERIES:
 Cells with lithium anodes are called Lithium batteries.
 Lithium primary cells can be broadly classified into 1.Primary cells with solid cathodes:
Ex: Li / MnO2 Cell and 2.Primary cells with liquid cathode: Ex: Li –SO 2 , LithiumThionyl chloride Cell
 (Secondary )Rechargeable lithium batteries: lithium batteries are characterized by
high specific energy (because of light weight of lithium) and high cycle life. These
batteries have either lithium foils as anodes (negatives) or lithiated transition metal oxides
as cathodes (positives) with solid polymer electrode. Electrolyte is immobilized
polymer electrolyte with polymer separators. Some lithium salts are soluble in polymers
such as polyethylene oxide, resulting in solution of sufficiently high thermal conductivity,
enabling the battery operation at temperatures as high as 50°C. Cathode materials such as
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LiMnO4, MnO2, TiS2, V6O13 are studied with polymer electrolyte lithium cells.
 Examples for lithium batteries :Li- TiS2, Li – sulphur ,Li – MnO2 , Li –V2O5 batteries.
 Lithium-titanium sulphide cell
The electrode and cell reactions of this cell are given below:
Anode: Lithium
Cathode:TiS2
Electrolyte: A solid electrolyte (Polymer packed between the electrodes which permits the
passage of ions but not electrons)
Anode:
Li → Li+ + eCathode:
Cell reaction:
TiS2 + e- → TiS2----------------------------Li + TiS2 → LiTiS2
-----------------------------
Cell Voltage: 3V
Lithium-Sulphur Battery:
 Litthium-Sulphur battery is a rechargeable battery. Its anode is made of Li. Sulphur is
the electron acceptor, the electron from Li is conducted to S by a graphite cathode. β–
Alumina (NaAl11O17) is used as the solid electrolyte.
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This solid electrolyte allows the Li + ions to migrate to equalize the charge, but will not
allow the big poly sulphide product ions. This battery is operated at high temperatures as Li and
S should be in their molten states.
At Anode: 2 Li →2Li+ + eAt Cathode : S + 2e- → S2Net reaction: 2 Li + S → 2Li+ + S2The direct reaction between lithium and sulphur is prevented by alumina present in the cell.
 Advantages of lithium battery:
a) Electrode potential ( Eo) of Li / Li + is most electronegative, So lithium battery generates
a high voltage (3.0) than all other batteries
b) Only 7 g( 1mol) of Li metal is needed to produce 1 mol of electrons during discharging
c) Lithium batteries can be made in different shapes and sizes
d) There is no risk of leakage from the lithium battery, since all its constituents are solid
 Applications: Lithium batteries are used in potable telephones, computers, and
camcorders. Lithium battery research is under progress for use in electric vehicle propulsion
and as energy storage devices. Example of such a battery system is FeS 2 (positive)– Li Al
(negative) cell with molten chloride electrolyte. These batteries are operated at 400°C.
Lithium sulphur battery is used in electric cars.
Session :25 :Fuel cells-types-hydrogen & oxygen fuel cell – Principle of working and
applications
 Introduction: Fuel cell is an electrochemical cell which converts the chemical energy of
fuel into electrical energy by an electrochemical process in which fuel materials are oxidized.
A fuel cell differs from a conventional battery that it requires continuous replenishment of
the fuel electrode, unlike recharging.
DEPT.OF APPLIED CHEMISTRY/SVCE
 The basic arrangement in a fuel cell can be represented as follows.
Fuel/ electrode/electrolyte/electrode/oxidant
 At the anode ,fuel undergoes oxidation, liberating electron and the oxidation products of
the fuel. The electron so liberated from the oxidation process reduce the oxidant at the
cathode. Thus movement of electrons constitute electric current. Varieties of fuel cells are in
use. The important types of fuel cells are hydrogen-oxygen fuel cell, methanol-air fuel cell,
phosphoric acid fuel cell etc.
 Hydrogen-oxygen fuel cell:
The electrodes of a fuel cell are referred to as fuel electrode and oxidant electrode. The
working of a hydrogen-oxygen fuel cell is based upon the reaction of hydrogen – fuel and
oxygen – oxidant to form water.
Construction: At the anode, hydrogen gas is diffused through a porous carbon electrode. The
surface of the carbon electrode is embedded with a catalyst such as finely divided platinum
or palladium. At the cathode, oxygen is diffused through a porous carbon electrode,
impregnated with cobalt oxide, platinum or silver as catalyst. The two electrodes are
separated by electrolyte such as KOH solution.
Working: As hydrogen gas diffuses through the anode, it is adsorbed on the electrode surface
in the form of hydrogen atoms and reacts with hydroxyl ions (of the electrolyte) to form
water.
At anode / fuel electrode:
H2 → 2 H+
2 H+ + 2 OH- → 2 H2O + 2 e--------------------------------------H2 + 2 OH- → 2 H2O + 2 e- (or) 2 H2 + 4 OH- → 4 H2O + 4 e---------------------------------------
DEPT.OF APPLIED CHEMISTRY/SVCE
The electrons released in the above process flow through the external circuit to the
cathode. The oxygen gas diffusing through the cathode, is adsorbed on the electrode surface,
where is reduced to hydroxyl ions.
At cathode / oxidant electrode:
O2 + 2 H2O + 4 e → 4 OHThe hydroxyl ions thus produced migrate through the electrolyte from the oxygen
(oxidant) electrode to the hydrogen (fuel) electrode. The electrolyte concentration remains
constant almost. The flow of electrons through the external circuit from the fuel electrode to
the oxidant electrode constitutes the electric output of the fuel cell (voltaic).
Thus the overall cell reaction of a hydrogen-oxygen fuel cell is the combination of hydrogen
and oxygen to produce water.
:
2 H2 + 4 OH- → 4 H2O + 4 e: O2 + 2 H2O + 4 e → 4 OH----------------------------------------------Overall cell reaction :
2 H2 + O2 → 2 H2O
----------------------------------------------Advantages: (i) high efficiency (ii) ability to operate on a variety of hydrocarbon fuels (iii)
no objectionable
emissions (iv) lesser land requirement compared to conventional power plants (v) direct
energy conversion
without intermediate wastage as heat.
An interesting application of hydrogen-oxygen fuel cell is that sunlight can be used to
decompose water hydrogen and oxygen, which can be used as the fuel cell input.
Anodic reaction
Cathodic reaction
DEPT.OF APPLIED CHEMISTRY/SVCE