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ENGINEERING CHEMISTRY

(22CH101)

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Table of Contents

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Table of Contents

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COURSE OBJECTIVES

Objectives:

• To understand the water quality criteria and interpret its applications in water purification

• To gain insights on the basic concepts of electrochemistry and implement its applications in

Chemical Sensors

• To acquire knowledge on the fundamental principle of energy storage devices and relate it to

Electric Vehicles.

• To identify the different types of smart materials and explore its applications in Engineering

and Technology

• To assimilate the preparation, properties and applications of nanomaterials in various fields

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UNIT III ENERGY STORAGE DEVICES AND ENERGY SOURCES 15

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Batteries – Primary alkaline battery - Secondary battery - Pb-acid battery, Fuel cell- H2 – O2 fuel cell. Batteries used in E- vehicle: Ni-metal hydride battery, Li-ion Battery, Li-air Battery Nuclear Energy – Nuclear fission, fusion, differences, characteristics – nuclear chain reactions – light water nuclear reactor – breeder reactor. .

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1. Determination of single electrode potential of the given electrode.

2. Estimation of the iron content of the given solution using a potentiometer.

3. Determination of electrochemical cell potential (using different electrodes/ different

concentrations of electrolytes)

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22CH101-ENGINEERING CHEMISTRY L T P C 3 0 2 4

COURSE OUTCOMES

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�Course Outcome mapping with POs / PSOs �

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LECTURE PLAN

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Activity Based Learning

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Role Play:

UNIT – III�ENERGY STORAGE DEVICES �AND �ENERGY SOURCES�

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Energy storage devices

3.1. Introduction:

Energy storage is the capture of energy produced at one time and can be used later. A device that stores energy is generally called as an accumulator or battery. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic. Various types of energy storage devices are fuel cells, batteries, capacitors, flywheels, compressed air, pumped hydro, super magnets, hydrogen, etc. 

3.1.1 History of battery:

Batteries have been with us for a long time. In 1938, the Director of the Baghdad Museum found the “Baghdad Battery” in the basement of the museum. During its analysis, it is dated around 250 BC and it is of Mesopotamian origin.

American scientist and inventor Benjamin Franklin first used the term "battery" in 1749 when he was doing experiments with electricity using a set of linked capacitors.

The first true battery was invented by the Italian physicist Alessandro Volta in 1800. Volta stacked discs of copper (Cu) and zinc (Zn) separated by cloth soaked in salty water.

Some of the first practical batteries used are:

• Daniel cell
• Bird’s cell
• Porous pot cell
• Gravity cell
• Poggendorff cell
• Grove cell
• Dun cell

One of the most enduring batteries, the lead-acid battery, was invented in 1859 and is still the technology used to start most internal combustion engine cars today. It is the oldest example of rechargeable battery. Later scientists found so many rechargeable batteries such as Nickel-cadmium battery, lithium and lithium-ion batteries etc.,

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Electrochemical Cell is a device that converts chemical energy into electrical energy. Wherever energy is needed, chemical reactions can be made to occur in the cell.

A battery is basically an electrochemical cell which is an arrangement of several electrochemical cells connected in series. These are devices that give direct current, maintaining a constant voltage. The battery's voltage is equal to the voltage of one cell multiplied by the number of such cells connected in series. In the battery the cells are arranged in such a way that the anode of one cell is connected to the cathode of the other cell.

3.1.2 Requirements of a battery:

• The voltage of the battery should not vary appreciably during its use.
• It should be light and compact for easy transport.
• It should have long life both when it is in use and not in use.
• High overall efficiency.
• Very low self-discharge.
• Low maintenance cost.
• Easy installation and operation.

3.1.3 Types of batteries:

2. Primary batteries:

In primary batteries, the electrode reaction cannot be reversed by passing an external electrical energy. The reactions occur only once and after use they become dead. Therefore they are not chargeable. Based on the standard size and capacity, they are classified as shown in figure below.

E.g. Daniel cell, Dry or Leclanche cell.

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2. Secondary batteries:

In this the electrode reactions can be reversed by passing an external electrical energy. Therefore they can be recharged by passing electric current and used again and again.

E.g. Pb-H₂SO₄ battery, Ni-Cad battery

3. Reserve battery or fuel cell:

Fuel cells are cells producing electrical energy from chemical energy produced out of the chemical reactions of different fuels.

E.g. H2-O2 fuel cells.

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3.2. Primary batteries:

3.2.1. Dry cell:

A dry cell is one type of electrochemical cells, which is generally used for the home and portable electronic devices. A dry cell was developed by the “German scientist Carl Gassner” in 1886 and modern dry cells were developed by Yai Sakizo, in 1887. Nowadays, the most commonly used batteries are dry cell batteries, which vary from large flashlight batteries to minimized flashlight batteries and are mostly used in wristwatches or calculators.

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Construction and working:

A dry cell consists of a zinc container whose base acts as a negative electrode (anode) and a carbon rod acts as a positive electrode (cathode). It is surrounded by manganese dioxide and low moisture electrolyte like ammonium chloride paste, which will produce a maximum of 1.5V of voltage and they are not reversible.

The electrode reactions are complex. Metallic Zn is oxidized to Zn²⁺ and the electrons liberated are left on the container. The reactions which take place at electrodes can be represented as below:

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At anode:   Zn_(s)​ → Zn²⁺_(aq) ^​ ​ + 2e^- (Oxidation)

Zn²⁺ +2 Cl ^- → ZnCl₂

^� Zn_(s) +2 Cl ^- → ZnCl₂ + 2e^-

At cathode:

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2NH₄⁺_(aq) ​+2MnO_2(s)​+2e⁻→ Mn₂O_3(s) ​+ H₂​O_(l) ​+ 2NH_3(g) (Reduction)​

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Overall reaction :

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Zn_(s)​ ​ + 2NH₄ Cl _aq) ​ + 2MnO_2(s) ​ → ZnCl_{2 (aq)} ​+ Mn₂O_3(s) ​+ H₂​O_(l) ​+ 2NH_3(g)

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• ZnCl₂ + 4NH_3(g) ​→ [Zn(NH₃​)₄​]Cl₂

The ammonia gas formed combines with ZnCl₂ and forms zinc ammonium chloride complex.

This reaction prevents polarization due to formation of ammonia. It also prevents the substantial increase of concentration of Zn²⁺ ions which would decrease the cell potential. The potential of dry cell is approximately 1.5V.��Drawbacks :

• Leakage of battery in a closed environment.
• Acidic nature of electrolyte NH₄​Cl, corrodes zinc container reduces the cell voltage.

3.2.2. Primary Alkaline Batteries :

An Alkaline battery is an improved form of the dry cell in which the electrolyte NH₄Cl is replaced by KOH, which is having more positive potential. This fact led to the development of many alkaline batteries. Commercial Duracell batteries are examples of alkaline batteries.

Specifications of Alkaline Batteries:

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Construction and Working:

Alkaline battery is an improved form of the dry cell, in which the electrolyte NH₄Cl is replaced by KOH. Alkaline battery consists of a zinc cylinder filled with an electrolyte consist of powdered KOH and MnO₂ (active cathodic material) in the form of paste using starch and water. A carbon rod (cathode) is immersed in the electrolyte in the centre of the cell for electrical contact for the flow of electrons. The outer cylindrical zinc body acts as anode.

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Cell reaction:

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The emf of the cell is 1.5V.

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At anode : Zn_(s)+2OH^-_(aq) ⎯→ Zn(OH)_2(s)+2e^-

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At cathode : 2MnO_2(s)+H₂O_(l)+2e^- ⎯→ Mn₂O_3(s)+2OH^-_aq

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 Overall cell reaction:

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Zn_(s)+ 2MnO_2(s)+H₂O_(l) ⎯→ Zn(OH)_2(s)+ Mn₂O_3(s)

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Advantages of Alkaline batteries:

The main advantages of alkaline cell over dry cell are:

• There is no leakage, since Zn does not dissolve readily in a basic medium.
• The shelf life of alkaline battery is longer than the dry battery, because there is no corrosion of Zn. An alkaline battery is expected to power a device for a period of two to four months (except in a few low-drain applications).
• Alkaline battery maintains its constant voltage, as the current is drawn from it.
• Alkaline batteries are environment-friendly, which can be disposed as trash and do not require active collection and recycling.
• The Wide choice of batteries offered by the manufacturers according to the applications (low-drain, medium-drain and high-drain batteries) makes it more advantageous.

Uses:

• Applications of low-drain alkaline batteries include flashlights, portable radios, alarm clocks, remote controls, and toys etc.
• Medical applications use alkaline batteries as power source in specific types of infusion pumps, pulse oximeters, blood pressure monitors, electronic thermometers and the like.
• Industrial applications of alkaline batteries involve usage in smoke alarms, portable transmitters, scanners, digital voltmeters, door locks, remote controls and laser pointers.
• Military and defense application include usage of alkaline batteries in SINCGARS, man pack radios and also in GPS systems.

[Note: Single Channel Ground and Airborne Radio System (SINCGARS) is a Combat Net Radio (CNR) currently used by U.S. and allied military forces]

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3.3. Secondary batteries:

In this the electrode reactions can be reversed by passing an external electrical energy. Therefore they can be recharged by passing electric current and used again and again.

E.g. Pb-acid battery, Ni-cad battery

3.3.1. Lead-Acid Storage Batteries:

The lead-acid battery represents the oldest rechargeable battery technology. Lead-acid batteries can be found in a wide variety of applications, including small-scale power storage such as UPS systems, starting, lighting, and ignition power sources for automobiles, along with large, grid-scale power systems. Recently, significant improvements in the cycle life of lead-acid batteries have been achieved through the incorporation of carbon into the negative plate. Carbon modification has provided new life to ageing lead-acid battery technology, enabling its use in hybrid vehicles as well as stationary storage.

A lead-acid storage cell is a secondary battery, which can operate both as a voltaic cell and as an electrolytic cell. This is the most commonly used battery in all automobiles to give power to the Ignition circuit.

Specifications of Lead-Acid Storage Batteries:

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Description:

A lead-acid storage battery consists of a number of voltaic cells (3-6) connected in series. In each cell the anode is made of lead. The cathode is made of lead dioxide PbO₂ or a grid made of lead, packed with lead dioxide. A number of lead plates (anodes) are connected in parallel and a number of PbO₂ plates (cathodes) are also connected in parallel. The plates are separated by an insulator made up of rubber, wood or fiberglass. The entire combination is then immersed in dilute H₂SO₄ (38% by mass).

The cell may be represented as:

Pb/PbSO₄ // H₂SO₄(aq) // PbO₂ / PbSO₄

Cell reactions: Dischrging

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At anode: Lead is oxidized to Pb²⁺ ions, which further combines with SO₄^2- forms insoluble PbSO₄.

Pb_(s) ↔ Pb²⁺_(aq) + 2e⁻

Pb²⁺_(aq)+SO₄²⁻_(eq) ↔ PbSO₄

Over all anode reaction: Pb_(s) + SO₄²⁻ ↔ PbSO_4(s) + 2e⁻

At cathode: PbO₂ is reduced to Pb²⁺ ions, which further combines with SO₄^2- forms insoluble PbSO₄.

PbO_2(s) + 2e⁻ + 4H⁺_(aq) ↔ Pb²⁺_(aq) + 2H₂O_(l)

Pb²⁺_(aq) +SO₄²⁻_(aq) ↔ PbSO_4(s)

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Over all cathode reaction: PbO_2(s) + 2e⁻ + 4H⁺_(aq) + SO₄²⁻_(aq) ↔ PbSO_4(s) + 2H₂O_(l)

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Overall cell reaction:

Pb_(s) + PbO_2(s) + 2H₂SO_4(aq) ↔ 2PbSO_4(s) + 2H₂O_(l)

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From the above cell reactions it is clear that PbSO₄ is precipitated at both the electrodes and H₂SO₄ is used up. As a result, the concentration of H₂SO₄ decreases so the battery needs recharging and also needs water, to compensate evaporation loss.

Recharging the battery:

The cell can be charged by passing electric current in opposite direction. The electrode reaction gets reversed. As a result Pb is deposited on anode and PbO₂ on the cathode. The density of H₂SO₄ also increases.

The net reaction during charging is

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Net cell reaction during both charging and discharging is

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Advantages:

• Inexpensive and simple to manufacture. 
• Mature, reliable and well-understood technology - when used correctly, lead-acid is durable and provides dependable service.
• The self-discharge is among the lowest of rechargeable battery systems.
• It produces very high current (Capable of high discharge rates).
• It acts effectively at low temperatures.

Disadvantages:

• Low energy density - poor weight-to-energy ratio limits use to stationary and wheeled applications.
• Cannot be stored in a discharged condition - the cell voltage should never drop below 2.10V.
• Allows only a limited number of full discharge cycles - well suited for standby applications that require only occasional deep discharges.
• Lead content and electrolyte make the battery environmentally unfriendly. 
• Transportation restrictions on lead acid batteries as there are environmental concerns regarding spillage.
• Thermal runaway can occur if improperly charged.
• It is too heavy for handling.
• It also leaks at times.

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3.3.2. Nickel metal hydride battery (NiMH or Ni–MH):

It is a type of rechargeable battery. Stanford Ovshinsky is the inventor of NiMH battery. In view of the environmental fears about Nickel Cadmium batteries and cells, Nickel Metal Hydride technology has taken over. The first consumer-grade NiMH cells became commercially available in 1989. In 2008, more than two million hybrid cars worldwide were manufactured with NiMH batteries.

Specifications of Nickel metal hydride battery:

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Applications:

1. The cell is used for automobile starting, lighting and ignition batteries.

2. It is used in large backup power supplies for telephone and computer centers, grid energy and off-grid household electric power systems.

3. They are used in backup power supplies for computer systems.

4. They are used as fuel in electric scooters, electric wheel chairs, electrified bicycles, marine applications, battery electric vehicles or micro hybrid vehicles, and motorcycles.

Description:

In this battery anode is porous nickel grid pasted with hydrides of metals like VH₂, ZrH₂ and TiH₂ with a hydrogen storage metal alloy such as TiN₂ or LaNi₅ (ie) hydrogen absorbing alloy is used as anode and cathode is nickel grid pasted with NiO(OH). The electrolyte is 28% KOH solution.

The cell representation is MH₂/M/KOH// NiO(OH)/Ni(OH)₂

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Working (Discharging):

When the NiMH battery operates the following reactions occur. NIMH system requires 10 series cells to reach potential of 12 V.

At Anode:

Metal hydride is oxidized with the liberation of electrons which then combine with hydroxide ion to form water.

MH_{2 (s)}+2OH^-_(aq) → M_(s) + 2 H₂O _(l)+2 e^-

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At Cathode:

Nickel oxyhydroxide is reduced to Ni²⁺ which further combine with H₂O to form Ni(OH)₂.

2 NiO(OH)_(s)+ 2 H₂O_(l)+ 2 e^- ↔ 2 Ni(OH)_2(l)+ 2 OH^-_(aq)

Overall cell reaction during use (discharging):

MH_{2 (s)} + 2 NiO(OH)_(s) ↔ M_(s)+ 2 Ni(OH)_2(l)

Recharging the battery:

The cell can be charged by passing electric current in opposite direction. The electrode reaction gets reversed. As a result MH₂ is deposited on anode and NiO(OH) on the cathode. The density of KOH also increases.

2 Ni(OH)_{2 (l)} + M_(s) ↔ 2 NiO(OH)_(s) + MH_{2 (s)}

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Advantages:

1. NiMH has less toxins and it is environment friendly.

2. It can be recycled.

3. It can be used in wide temperature range.

4. It has 30 – 40 percent higher capacity and energy density over a standard Ni-Cd battery.

5. It is much safer than lithium batteries.

6. It has less memory effects than nicad

Disadvantages:

1. More complex charge algorithm needed-NiMH generates more heat during charge.

2. This battery deteriorates during long time storage.

3. Deep discharge reduces the life cycle and produces heat when it is fast charged and high load discharge.

4. Self-discharge is more compared to other batteries.

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5. High maintenance is required, it should be often fully discharged to prevent crystalline formation.

6. Expensive than Ni-Cad battery.

Applications:

It is used in

• Low cost consumer applications.
• Electric vehicles.
• Space crafts.
• High power static applications.
• Commercial and industrial portable products.
• Medical instruments and equipment.
• Toys, cameras, mobile phones etc.,

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3.3.3. Lithium Batteries:

Chemists worked on the idea for the lithium battery in 1912, but first commercial Li battery was available only in 1970 and these batteries were not rechargeable. The chemical instability of lithium metal made rechargeable lithium batteries too difficult to develop. In 1991, scientists used more stable lithium compounds to create a battery. This lithium ion battery was rechargeable and lighter in weight than other rechargeable battery technologies available at the time.

There are two types of Lithium based batteries:

1. Lithium-Batteries:

Li-batteries are primary batteries that have metallic lithium as an anode and a reductive material as cathode . These types of batteries are also referred to as lithium-metal batteries.

ii) Lithium-ion batteries:

Li-ion batteries are secondary batteries that have Lithium compounds are used as cathode. Lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Because of this reason, the lithium ion batteries are called Rocking chair, Swing cells.

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Comparison of Li and Li-ion batteries:

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1. Lithium batteries are a primary cell and lithium ion batteries are secondary cells.
2. Lithium batteries are not easily and safely rechargeable; this problem led to the invention of lithium ion batteries. They can be charged several times before becoming ineffective. 
3. Li batteries have a higher energy density than lithium ion batteries.
4. Lithium batteries use lithium metal as their anode unlike lithium ion batteries that use a number of other materials to form their anode.
5. Both types of batteries offer a lot of power for their size. They can be used in any number of devices from flashlights to compact disc players.
6. Their recharge ability makes them ideal power sources in consumer electronics.
7. Lithium batteries are the battery of choice when it comes to powering artificial pacemakers because of their long life and the amount of energy they offer.
8. Lithium batteries work well as long-term power sources in devices that are out of reach, such as smoke detectors and computer motherboards.

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3.3.4. Lithium - ion battery:

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The cell specification is as follows:

Construction:

Lithium ion secondary battery depends on an “intercalation” mechanism. This involves the insertion of lithium ions into the crystalline lattice of the host electrode without changing its crystal structure. Lithium ion batteries consist of a Lithium Metal Oxide positive electrode (cathode) with thin aluminum foil as current collector, graphite negative electrode (anode) and electrolyte of a lithium salt in alkyl carbonate solution.

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The cathode is made of transition metals oxides or phosphates as active material such as:

• Lithium Cobalt Oxide – LiCoO₂
• Lithium Iron Phosphate – LiFePO₄
• Lithium Manganese Oxide – LiMnO₂
• Lithium Nickel Manganese Cobalt Oxide – LiNi_xMn_yCo_zO₂

Li-ion cell has a four-layer structure. Cathode and anode are separated by a membrane made of polypropylene or polyethylene filled with electrolyte which contains lithium salts (i.e. LiPF₆) in ethylene or propylene carbonate at different ratio. The separator prevents the electrical contact between the electrodes and at the same time, it allows the diffusion of Li-ions from cathode to anode during the charging and the reverse discharging process.

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Working:

During discharge Li ions are dissociated from the anode (negative plate) and migrate across the electrolyte and are inserted into the crystal structure of the host compound of cathode.

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For example in Lithium Cobalt Oxide (LiCoO₂) the discharge mechanism is as follows:

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Advantages:

1. They have high energy density than other rechargeable batteries.
2. Available in various shapes and sizes and lighter in weight.
3. There is no requirement for priming like in nickel batteries.
4. Do not suffer from memory effect.
5. They possess low self discharge rate (5–10% per month).
6. They are lighter than other battery types.

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7. They produce high voltage out about 4 V as compared with other batteries.
8. No liquid electrolyte (i.e., they are immune from leaking)
9. Low maintenance cost.
10. Lithium ion batteries can be formed into many shapes which makes them ideal for items such as laptop computers, iPods and cell phones.

Disadvantages:

1. They are expensive.
2. The capacity diminishes with charging and ageing.
3. Internal resistance increases with charging and ageing.
4. Undergo explosion when contacts with air/moisture.

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Applications:

Lithium batteries have a long list of real-world applications, from life-saving medical equipment to luxury yachts, lithium batteries keep both the essentials and the comforts of modern life running with safety and reliability.

1. Emergency Power Backup Or UPS (Uninterruptible Power Supply):

Emergency power backup systems benefit critical equipment, computers, communication technology and medical technology.

2. Solar Power Storage:

Lithium batteries used for solar power storage.

3. Dependable Electric And Recreational Vehicle Power:

With a lifespan of over ten years, lithium batteries provide power for long journeys. Lightweight lithium batteries power electric vehicles with increased efficiency due to reduced weight and size as compared to lead acid batteries.

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4. Reliable And Lightweight Marine Performance:

Long-lasting rechargeable lithium battery power a small trolling motor or power all of the conveniences of home on a yacht.

5. Mobility Equipment:

Lightweight lithium batteries are the ideal choice for mobility equipment, from electric wheelchairs to stair lifts. They offer size customization, a longer life span, fast charging, a low self-discharge rate and extended run time.

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6. Portable Power Packs:

Rechargeable lithium batteries are well-known for powering our phones and the latest lightweight laptop computers. They tolerate movement and temperature changes, as well as maintain their power delivery during use.

7. The Li-ion batteries are used in cameras, calculators.
8. They are used in cardiac pacemakers and other implantable device.

Lithium-air (Li-air)

• The lithium-air battery (Li-air) is a metal–air electrochemical cell. Lithium–air batteries are the most promising system, because of their far higher theoretical specific energy density (12 kWh/kg) than conventional batteries. Electric vehicles (EVs) welcomes the high energy density batteries. Pd/ MnO₂ and α-MnO₂/Pd catalyst are used at cathode.

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• Lithium air batteries based on the electrolyte used can be classified into four types:
• Fully Aprotic (Non-aqueous electrolytes)
• Aqueous electrolytes
• Hybrid electrolytes [Combination of (a) & (b) or (d) ]
• Solid state electrolytes

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Construction and Working:

• Aprotic Li-air battery has the simplest design. The anode is Li metal dipped in organic electrolyte. Upon charging/discharging in aprotic cells, layers of lithium salts precipitate onto the anode, eventually covering it and creating a barrier between the lithium and electrolyte.
• Porous carbon cathode with Pd/MnO2 catalyst are used. The lithium ions move between the anode and the cathode across the electrolyte.
• Under discharge, electrons follow the external circuit to do electric work and the lithium ions migrate to the cathode. During charge the lithium metal plates onto the anode, freeing O₂ at the cathode.

Aprotic Li-Air Battery

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Advantages:

1. The energy density per unit mass of non-aqueous lithium–air batteries is about 10 times higher than those of lithium-ion batteries

2. Li metal anode needs no protection as it does not react with organic electrolyte

Disadvantages:

1. The Li₂O₂ produced at the cathode is insoluble in the organic electrolyte, leading to buildup along the cathode/electrolyte interface. This makes cathodes to clog and leading to volume expansion
2. Reduces conductivity and degrades battery performance.
3. Organic electrolytes are flammable and can ignite if the cell is damaged.

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4. Air free of water vapour is required

5.Chemical stability of cell component is poor

Lithium-Air batteries will primarily remain a research topic for at least the next five years. Even if the challenges are successfully addressed in that time period, the stringent requirements of durable and safe operation in an automotive environment will further delay commercialization.

3.4. Fuel cells:

Fuel cell is a device that converts the chemical energy of a fuel directly into electricity by electrochemical reactions. A fuel cell resembles a battery in many respects, but it can supply electrical energy over a much longer period of time, because a fuel cell is continuously supplied with fuel and air (or oxygen) from an external source. Hence, fuel cells have been used for decades in space probes, satellites, and manned spacecraft. Around the world thousands of stationary fuel cell systems have been installed in utility power plants, hospitals, schools, hotels, and office buildings for both primary and backup power; many waste-treatment plants use fuel cell technology to generate power from the methane gas produced by decomposing garbage.

Fuel + oxygen → oxidation products + Electricity

Different types of fuel cells are

• Polymer electrolyte membrane fuel cells
• Direct methanol fuel cells
• Alkaline fuel cells
• Phosphoric acid fuel cells
• Molten carbonate fuel cells
• Solid oxide fuel cells
• Reversible fuel cells

3.4.1. Hydrogen – Oxygen Fuel Cell:

Hydrogen-oxygen fuel cell is the simplest and most successful fuel, which uses the fuel hydrogen and the oxidizer-oxygen with the electrolyte. Other fuels include hydrocarbons and alcohols. Other oxidants include chlorine and chlorine dioxide. The cell releases the energy from hydrogen by reacting with oxygen, not as heat as in normal combustion with air, but as useful electrical energy i.e. a practical electricity supply.

Specifications of H₂- O₂ Fuel Cell:

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Construction:

The cell has two porous electrodes, anode and cathode. The electrodes are made of compressed carbon containing a small amount of catalyst (Pt,Pd,Ag) impregnated in it. In between the two electrodes an electrolyte solution such as 25% KOH or NaOH is filled. The two electrodes are connected through the voltmeter.

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Working of the cell:

The fuel hydrogen is bubbled through the anode compartment, where it is oxidized. The oxidizer oxygen is bubbled through the cathode compartment, where it is reduced.

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Cell Reactions :

• At anode: Hydrogen gas, passed through the anode, is oxidized with the liberation of electrons which then combine with hydroxide ions to form water.

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At Cathode: The electrons, produced at the anode, pass through the external wire to the cathode where it is absorbed by oxygen and water to produce hydroxide ions.

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Overall cell reaction:

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The emf of the cell = 1.0 V

Fuel Battery:

When a large number of fuel cells are connected in series, it forms a fuel battery.

Advantages of fuel cells:

• Fuel cells are efficient (75%) and take less time for operation.
• It is pollution and noise free technique.
• It produces electric current directly from the reaction of fuel and an oxidizer.
• It produces drinking water.

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5. Hydrogen-oxygen fuel cells are much efficient than conventional power stations or batteries (e.g. zinc-carbon) because the electrical energy is directly generated from the chemical reaction between the oxidant and the fuel - there are no complications like turbines and generators.

6. With a fuel cell there are fewer stages in producing the useful energy, so there is less opportunity to lose potentially useful energy i.e., like wastage of heat, friction from moving parts etc.

7. They are highly efficient in energy conversion and instant in operation.

8. Fuel cell holds promises in the energy scenario, replacing to some extend fossil fuel.

Disadvantages:

1. Fuel cells cannot store electric energy as other cells do.

2. Electrodes are expensive and short lived.

3. Storage and handling of hydrogen gas is dangerous.

4. High initial cost.

5. Large weight and volume of H₂ and O₂ gas storage.

6. Porous electrodes are affected by CO₂ hence gases should be free from CO₂.

7. H₂ should be pure.

Applications:

• H₂- O₂ fuel cells are used as auxiliary energy source in space vehicles like Apollo space program and also in submarines.
• The product water is proved to be a valuable source of fresh water by the astronauts.

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3. Currently, extensive research is being conducted in order to manufacture a cost efficient automobile which is powered by a fuel cell.

4. Fuel cell electric vehicles use clean fuels and are therefore more eco-friendly than internal combustion engine-based vehicles.

5. Generally, the byproducts produced from these cells are heat and water.

6. The portability of some fuel cells is extremely useful in some military applications.

7. These electrochemical cells can also be used to power several electronic devices.

8. Fuel cells are also used as primary or backup sources of electricity in many remote areas.

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E- Vehicles

The major air pollution specifically in cities are caused by passenger vehicles. They let out tail pipe pollutants like carbon monoxide, nitrogen oxides and other pollution. In addition the transport sector is responsible for about 28% of the total carbon dioxide (CO₂) , a green house gas emissions as per European union report, On the other hand limited oil reservoirs pressurises research and government to take an alternative steps to address the problems. The alternative solution provided by researcher and action taken by government is to shifting towards e vehicle. The advantages of e-vehicle are

1. Zero emissions: The combustion product like CO₂ and NO₂ is eliminated from vehicles. The chemical reaction in batteries doesn’t lead to any emission of gases.
2. Simple Engine Design: The engines design is simple as neither need of a cooling circuit, nor for incorporation, clutch , gearshift, or elements to reduce the engine noise.
3. Increase in reliability: Simple engine technology hence fewer breakdowns.
4. Maintenance Cost: The maintenance cost much lower for EVs than conventional vehicle.
5. Comfort of traveling in EVs, due to the absence of vibrations or engine noise.
6. Efficiency: EVs fed by renewable energy show an higher overall efficiency up to 70% but EVs fed by a natural gas power plant show a the overall well to wheel WTW efficiency that ranges from 13% to 31.

Evs challenges and the area of improvement required:

1. Driving range is limited from 200 to 350 km with a full charge, although this issue is being continually improved. The Tesla Model S has shown a driving range greater than 500 km.

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2. Full charging the battery pack can take 4 to 8 h. Even a “fast charge” to 80% capacity can takes 30 min. For example, Tesla super chargers can charge the Model S up to 50% in only 20 min, or 80% in half an hour.

3. Large battery packs are expensive and are heavy 200 kg and take up considerable vehicle space

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TYPES OF E-VEHICLES

The types of electric vehicle involves for various purpose are as follows

1.  Battery Electric Vehicles (BEVs): These are powered by 100% electric power. BEVs do not have an internal combustion engine and hence no fossil fuel is required. A typical travelling BEV can make a travel of 160 to 250 km, although some of them can travel as far as 500 km with just one charge. Currently Nissan Leaf, of 62 kWh battery provides an autonomy of 360 km.

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2. Plug-In Hybrid Electric Vehicles (PHEVs):

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The vehicles are propelled by both combustible engine and an electric engine charged by a pluggable external electric source. PHEVs can reduce the fuel consumption significantly by partly using electric charge. This will reduce the travel range challenge in BEVs. The Mitsubishi Outlander PHEV provides a 12 kWh battery, which allows it to drive around 50 km just with the electric engine.

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Hybrid Electric Vehicles (HEVs): The hybrid vehicles are propelled by a combination of a conventional internal combustion engine and an electric engine. The energy that powers the batteries are gained through regenerative braking or while driving using the combustion engine. The Toyota Prius, in its hybrid model (4th generation), provided a 1.3 kWh battery that theoretically allowed it an autonomy as far as 25 km in its all-electric mode.

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Fuel Cell Electric Vehicles (FCEVs): The vehicle are powered by hydrogen oxygen fuel cell. In this the chemical reaction occurs without combustion with product as water. These provides zero emissions. It is worth highlighting that, although there is green hydrogen, most of the used hydrogen is extracted from natural gas. The Hyundai Nexo FCEV [28] is uses fuel cell being able to travel 650 km without refuelling.

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Extended-range electric vehicles: (ER-EVs) vehicles are very similar to those ones in the BEV

category. However, the ER-EVs are additionally provided with a supplementary combustion

engine, which charges the batteries and not connected to the wheels of the vehicle. An example of this type of vehicles is the BMW i3, which has a 42.2 kWh battery that results in a 260 km autonomy in electric mode, and an additional 130 km is benefitted from the extended-range mode.

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Types of Batteries used in automobiles

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Lead-acid batteries (Pb-PbO2): It is the oldest kind of rechargeable battery. It is initially used as SLI (starting lighting and igniting) battery in automobiles. It has also been used in electric vehicles. It has very low specific energy and energy density ratios as shown in below figure. The battery is formed by lead grid pasted with leadsulphate as eletrodes flooded with sulfuric acid. During the initial loading process, the lead sulfate is reduced to Pb in the negative plates, while, in the positives, lead oxide is formed (PbO2).The sulphuric acid density is 1.2g/cc indicates the fully charged state. For example the GM EV1 and the Toyota RAV4 EV, are vehicles that used this kind of batteries.

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Nickel-cadmium batteries (Ni-Cd). This technology was used in the 90s, as these batteries have a greater energy density, but they present high memory effect, low lifespan, and cadmium is a very expensive and polluting element. Hence these are substituted by nickel-metal-hydride (NiMH) batteries.

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Nickel-metal-hydride batteries (Ni-MH): Negative electrode is made up of spongy nickel alloyed with metal hydride replacing cadmium. It shows high energy density. They show higher level of self discharge than Nicad, these batteries are used by many hybrid vehicles, such as the Toyota Prius, the second version of the GM EV1 and the Toyota RAV4 EV.

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Sodium sulfur batteries (Na-S): which contain sodium liquid (Na) and sulfur (S). It possess high energy density, high loading and unloading efficiency of 90%, and a long life cycle. The functioning temperatures is between 300 and 350^oC . It was used in the Ford Ecostar, the model that was launched in 1992–1993.

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Zinc-bromine batteries (Zn-Br2): In these types of batteries use zinc-bromine solution stored in two tanks, and in which bromide turns into bromine in the positive electrode. This technology was used by a prototype, called ”T-Star”, in 1993.

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Lithium-ion batteries (Li-Ion). In this battery intercalated lithium ion in carbon layer swings between negative plate to positive while discharging and positive to negative plate while charging. The advantages are light weight, low internal resistance, with high cycle life. They must operate within a safe and reliable operation area, restricted by the temperature (<130^oC)and voltage windows, violating may lead to firing of battery.

This type of battery is the most used today by the majority of EVs and PHEVs.

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Charging Modes

The international standard for charging electrical vehicles. Four modes to charge the vehicles.

Mode 1 (Slow charging): It is domestic charging mode, with a maximum intensity of 16 A, and it uses a either single-phase or three-phase power outlet with phase(s), neutral, and protective earth conductors.

Mode 2 (Semi-fast charging): It can be used at home or in public areas, it has maximum intensity of 32 A, and rest similar to the previous mode.

Mode 3 (Fast charging): It supply an intensity between 32 and 250 A. It requires the use of an EV Supply Equipment (EVSE), which provides communication with the vehicles, monitors the charging process, incorporates protection systems, and stops the energy flow when the connection to the vehicle is not detected.

Mode 4 (Ultra-fast charging): A direct connection of the EV to the DC supply network with a power intensity of up to 400 A and a maximum voltage of 1000 V, which provides a maximum charging power up to 400 kW.

3.5.1. Introduction:

The discovery of the nuclear fission of Uranium by Otto Hahn (1938), opened a new era in the field of electrical energy generation.

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Fossil fuels are the energy sources in generating electrical energy, which is severely depleted and will last for another two to three decades only. At present the need for electrical energy increases rapidly and to meet out the requirement, alternate energy sources must be discovered. Nuclear energy is one of the best alternative energy sources for fossil fuels. Enormous energy is stored in the nuclear fuels that can be used in generating electrical energy.

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Terms and Terminology:

Radioactivity: The phenomenon of spontaneous and continuous emission of powerful invisible radiation by the disintegration of an element with atomic number more than 82 is called radioactivity. It affects the photographic plate. The most common types of radiation are called alpha, beta, and gamma radiations.

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3.5. Nuclear Chemistry

Mass defect (Δm):

The nuclear reactions always accompany a slight change in masses of products and that of reactants. This difference is known as mass defect.

Δm = mass of reactants - mass of products

E = (Δm) x C²

This loss of mass is converted into energy. The energy released is called binding energy.

Binding Energy: The energy released during the formation of nucleus with the constituent nucleons. In other words, the minimum energy is required to break the nucleus into its constituent nucleons. Greater the binding energy greater is the stability. It is expressed in MeV/ nucleon.

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Did you know?

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• On June 27, 1954, the world's first nuclear power station, the Obninsk Nuclear Power Plant, started its operations in Obninsk of the Soviet Union to generate electricity. 
• The world's first full scale power station, Calder Hall in England, opened on October 17, 1956.
• Nuclear energy now provides about 10% of the world's electricity from about 440 power reactors.
• Nuclear energy is the world's second largest source of low-carbon power (29% of the total in 2017). 
• Over 50 countries utilise nuclear energy in about 220 research reactors.

(Source: world-nuclear.org)

Nuclear energy: The energy released during nuclear reaction i.e., by the nuclear fission or nuclear fusion is called nuclear energy. During the nuclear chain reaction (fission reaction) of heavy isotope like ²³⁵U or ²³⁹Pu, enormous amount of energy is released, which is known as nuclear energy.

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Applications of nuclear energy:

• Electricity generation:

Nuclear energy is an environmental friendly energy resource for power generation.

• Source of pure water:

The water discharged from the nuclear reactors if free from radiation , then it can be used as a source of water.

• Health care:

Radioactive isotopes (nuclear energy) find use in treatment of cancer by radiotherapy. It is also used for sterilization to destroy microorganism.

• Agriculture:

It is used to control agricultural pests. Nuclear radiation delays ripening of fruits.

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Hazards of using nuclear energy:

• The radiation is harmful to the living organisms.
• The long and constant exposure of living organisms to these radiations cause the following diseases:
• The nuclear radiation can damage the structure of cells in the human body.
• It causes blindness and cancer.
• It causes genetic disorder in a human body. It causes sterility in young generation.

Mass - Energy Relation:

The energy released during the nuclear reaction is due to the loss in mass. The energy changes associated with nuclear reactions are determined by using Einstein’s Mass - Energy Relation.

Einstein’s Mass - Energy Relation:

E = mc²

Where, E = Energy equivalent

m = Mass

c = Velocity of light

For a change of 1 amu (atomic mass unit)

E = 931 MeV [1 amu = 931 MeV of energy]

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3.5.2. Nuclear reactions:

The reaction which brings about the changes in the nucleus of an atom is called nuclear reaction. There are two types of nuclear reactions namely

• Nuclear fission
• Nuclear fusion

3.5.2.1. Nuclear fission:

The process of splitting of heavy nucleus into two or more lighter nuclei by bombarding with a projectile like neutron is called nuclear fission reaction. During this reaction enormous amount of energy is released along with the emission of two or more secondary neutrons.

E.g.

²³⁵U₉₂ + ¹n₀ → [ ²³⁶U₉₂] → ¹⁴⁰ Ba₅₆ + ⁹³Kr₃₆ + 3¹n₀ + Energy

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Types of nuclear fission reactions:

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Characteristics of Nuclear Fission Reactions:

1. Heavy nuclei like ²³⁵U, ²³⁹Pu splits into two or more nuclei or fission fragments by absorbing slow moving neutrons.
2. Fission reactions liberates huge amount of energy.

E.g. 1 kg of ²³⁵U releases 2 X 10⁷ kWh energy.

3. Fission fragments are radioactive elements.
4. The atomic mass of fission products ranges from 70 to 160.
5. Fission reactions are self propagating chain reactions, because fission products contain secondary neutrons which further cause fission reactions, producing more secondary neutrons. Thus the fission reaction propagates.
6. The main criteria to propagate the chain reaction is the amount of fissionable material should be in sufficient amount. Other wise neutron will escape from the surface.

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• NUCLEAR FISSION
• Uncontrolled Fission Reactions
• If a nuclear fission reaction is made to occur in an uncontrolled manner, then the energy released can be used for many destructive purposes.
• E.g. Atom bomb
• Controlled Fission reactions
• If a nuclear fission reaction is made to occur in a controlled manner, then the energy released can be used for many constructive purposes.
• E.g. Nuclear reactor

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a. Critical mass: The minimum amount of fuel required to undergo a chain reaction is called critical mass .

Illustration:

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b. Super critical mass: If the mass of the fuel material is more than the critical mass, it is called super critical mass.

c. Sub critical mass: If the mass of the fuel material is less than the critical mass, it is called sub critical mass.

(Note: The mass greater or less than the critical mass will hinder the propagation of the chain reaction).

7. The nuclear chain reaction can be controlled by absorbing (by using Cd /B /Borosteel) desired number of neutrons and energy can be produced in controlled manner.

8. Multiplication Factor: The number of neutrons resulting from a single fission reaction is known as the multiplication factor. When the multiplication factor is less than 1 then the chain reaction does not takes place.

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Advantages of nuclear fission over fossil fuels:

• A small amount of nuclear fuel gives large amount of energy, while large quantity of fossil fuel is required to produce large amount of heat.
• In a nuclear power plant, the nuclear fuel is inserted once, it provides energy for a longer period of time, but in a thermal power plant fossil fuel must be supplied continuously to get the energy.

Disadvantages of nuclear fission over fossil fuels:

• Nuclear fission causes more serious pollution problem than the burning of fossil fuel.
• The biggest problem of using nuclear fission energy is a safe disposal method of nuclear waste, but no such problem is faced in the disposal of fossil fuel. 

3.5.2.2. Nuclear fusion or Thermonuclear reaction:

A process of combination of lighter nuclei to form heavier nucleus, with the release of enormous amount of energy is called nuclear fusion.

E.g. ²H₁ + ³H₁ ⁴He₂ +¹n₀ + Energy (23 x 10⁸ kJ/mol)

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Characteristics of nuclear fusion:

1. Nuclear fusion is possible only when the distance between the nuclei is of the order of one Fermi.
2. Fusion between the nuclei is opposed by the repulsive positive electrical charge common to all nuclei because they contain protons.
3. In doing so, they release a comparatively large amount of energy that arises from the binding energy, creating an increase in temperature of the reactants. 
4. The amount of energy in fusion is four times more compared to that of fission.
5. Sufficient amount of kinetic energy must be provided to facilitate a fusion reaction.
6. As electrostatic repulsion increases with increase in atomic number of nuclei, only lighter nuclei can undergo nuclear fusion reaction.
7. Fusion requires temperatures about 100 million Kelvin (approximately six times hotter than the sun's core). At these temperatures, hydrogen exists as plasma, and not a gas. Plasma is a high-energy state of matter in which all the electrons are stripped from atoms and move freely about.
8. The fusion reactions in the Sun takes place at about 100 million degrees centigrade.
9. Thus, temperature of high order would have to be reached. Hence fusion reactions are also called thermonuclear reactions.
10. The strength of nuclear fusion is that it creates less radioactive material than fission, and its supply of fuel can last longer than the sun.

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Did you know ?

Since the 1930s, scientists have known that the Sun and other Stars generate their energy by nuclear fusion. They realized that if fusion energy generation could be replicated in a controlled manner on Earth, it might very well provide a safe, clean, and inexhaustible source of energy. The 1950s saw the beginning of a worldwide research effort to develop a fusion reactor.

Differences between Nuclear fission and Nuclear fusion:

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Nuclear Chain Reaction:

In the nuclear fission reactions, the neutrons emitted from the fission of ²³⁵U atom may hit another ²³⁵U nucleus and cause fission producing more neutrons called secondary neutrons. Thus a chain of self-sustaining nuclear reactions will be set up with the release of enormous amount of energy. In a fission reaction the neutrons from the previous step continue to propagate and repeat the reaction is called nuclear chain reaction.

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Reasons for lesser energy:

Some of the neutrons released in the fission of ²³⁵U may escape from the surface to the surroundings (or) may be absorbed by ²³⁸U present as impurity. This will result in breaking of the chain and the amount of energy released will be less than the expected.

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Criteria for Nuclear Chain reaction:

To carry out nuclear chain reaction sufficient amount of ²³⁵U must be present to capture the neutrons; otherwise neutrons will escape from the surface.

When ²³⁵U nucleus is hit by thermal neutrons then it undergoes the following reaction with the release of three neutrons.

²³⁵U₉₂ + ¹n₀ → [ ²³⁶U₉₂] → ¹⁴⁰ Ba₅₆ + ⁹³Kr₃₆ + 3¹n₀ + Energy

Each of the three neutrons produced in the above reaction strikes another ²³⁵U nucleus causing (3 x 3 = 9) subsequent reactions. This process of propagation of the reaction by multiplication in threes at each fission is called chain reaction.

Nuclear reactor:

The device in which a nuclear fission reaction is made to occur in a controlled manner is called nuclear reactor. The energy released can be utilized for constructive purposes like generation of electricity.

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Nuclear reactors serve three general purposes:

Civilian reactors are used to generate energy for electricity and sometimes also steam for district heating; 

Military reactors create materials that can be used in nuclear weapons;

Research reactors are used to develop weapons or energy production technology, for training purposes, for nuclear physics experimentation, and for producing radioisotopes for medicine and research.

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Did you know?

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• 1 kilogram of coal generates about 8 kilowatts of electricity. 
• 1 kilogram of Uranium -235 can generate over 24 million kilowatts of electricity

3.6. Light Water nuclear reactor:

In light water nuclear reactor, water acts as coolant as well as moderator in which ²³⁵U fuel rod is immersed. Components used in light water nuclear reactor are fuel rod, control rod, moderator, coolant, reflectors, pressure vessel, protective shield, heat exchanger and turbine.

Components in Nuclear Reactor:

1. Fuel Rod:

The fissionable materials used in the nuclear reactor are enriched ²³⁵U or ²³⁹Pu in the form of rods or strips. The fuel is usually cladded in a metal jacket made of Al, Mg, Zr, (or their alloys) or stainless steel.

2. Control Rod:

The nuclear chain fission reactions are controlled by the control rods which are suspended between fuel rods. These are neutron absorbing materials and are not radioactive materials as a result of neutron capture. Control rods are regulators of the fission reaction which can be lowered or raised and control the fission reaction by absorbing excess neutrons. If the rods are deeply inserted inside the reactor, they will absorb more neutrons and the reaction becomes slow. If the rods are taken out, the reaction will be very fast. E.g. cadmium (Cd), Boron (B).

¹¹³Cd₄₃ + ₀n¹ → ¹¹⁴Cd₄₃ + γ-ray

¹⁰B₅ + ₀n¹ → ¹¹B₅ + γ-ray

3. Moderator:

Nuclear fission produces fast neutrons with a mean energy of 2 MeV (i.e. 20,000 km/s). If the velocity of fast neutrons is not reduced, the reaction will become uncontrollable. To slow down these neutrons, moderators are employed. The moderators slow down neutrons (0.2 eV, 2.2 km/s) in a small fraction of second. When the fast moving neutrons collide with moderator, they lose energy and get slow down.

E.g. Ordinary water, heavy water, graphite, beryllium etc.,

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Illustration of moderator:

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4. Coolants:

The enormous amount of heat produced in the reactor is removed by the coolants. The coolant should have high specific heat capacity, high thermal conductivity and stable at high temperature. The coolant is circulated in the reactor core and heat carried by coolant is used to produce steam.

E.g. Water used as coolant in light water nuclear reactor (but other reactors may use even heavy water, liquid metal (Na or K) or CO2 gas)

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5. Pressure vessel:

The pressure vessel encloses the core and is capable of withstanding pressure as high as 200 Kg/cm². The control rods are inserted through the holes at the top of the pressure vessel. It provides entrance and exit passage for coolants.

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6. Protective shield:

The nuclear reactor is surrounded by biological shield which is a concrete wall of more than 10 meter thick. The radiations like γ-rays and neutrons that escaped from the reactor (if any) are absorbed by the concrete shield and thus protect the environment and operative personnel from destruction in case of radiation leakage.

• Thermal shield: The thermal shield is made up of steel or iron sheet of 50–60 cm thickness. It is next to the pressure vessel. It absorbs most of the gamma rays and get heated up and cooled with a coolant.
• Biological shield: It is a layer of thick concrete surrounding the thermal shield. It absorbs the remaining gamma rays and neutrons to ensure safety for the operating personnel.
• Heat exchanger:

Heat exchangers transfer the heat liberated by the reactor to sea water. Steam is produced at a pressure of 400 kg/cm².

8. Turbine:

The steam produced by the heat exchangers, is used to operate steam turbine which drives the generator to produce electricity.

Working of light water nuclear reactor:

The fission reaction is controlled by inserting or removing the control rod of B or Cd. The heat emitted by fission of ²³⁵U in the fuel core is absorbed by the coolant water. The coolant takes up the heat (~ 300 °C) then goes to the heat exchanger and transfer the heat to sea water, which is converted into steam. The steam then rotates the turbines, connected with generator which generates electricity.

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Did you know?

Startup neutron source is a neutron source used for stable and reliable initiation of nuclear chain reaction in nuclear reactors, when they are loaded with fresh nuclear fuel. E.g. Californium-252, Plutonium-238 & beryllium, americium-241 & beryllium, polonium-210 & beryllium, radium-226 & beryllium.

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Core of CROCUS, a small nuclear reactor used for research  in Switzerland

Source: World Nuclear Association – Nuclear core

Advantages and Disadvantages of nuclear reactor:

Fuel assembly

3.7. Breeder reactor:

A breeder reactor is the one which converts non-fissionable or fertile material (²³⁸U, ²³²Th) into fissionable (or) fissile material (²³³U, ²³⁹Pu). During the reaction fast moving neutrons generated by ²³⁵U are utilized to convert fertile material ²³⁸U into fissile material ²³⁹Pu. Thus, the breeder reactor produces or breeds more fissile material than it consumes. In order to create a fissionable material, a fertile material is used, which is a material that will absorb a neutron and result in new fissionable material. The new fissionable material can produce more neutrons by fission, and thus can continue the fission process. The fertile materials thorium-232 and uranium-238 can produce fissionable ²³³U and ²³⁹Pu respectively.

• Fissile and fertile material:

The material which undergoes fission by slow moving neutron is called as fissile material. E.g. ²³⁵U, ²³⁹Pu, ²³³U, ²⁴¹Pu

Materials which do not undergo fission easily, but may be made fissile by bombardment with fast moving neutrons are called as fertile material. E.g. ²³⁸U, ²³²Th.

• Reaction Mechanism:

A primary fertile material like ²³⁸U is bombarded with fast moving neutrons and it absorbs a neutron to become ²³⁹U. This undergoes β-decay and forms ²³⁹Np (Neptunium) which undergoes further β-decay to give ²³⁹Pu (Plutonium). Pu is a secondary fissile material used as fuel in nuclear reactor. The burning up of primary fuels may be compensated by the production of new or secondary fissile fuels. The extent of compensation is measured by factor called conversion factor.

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Illustration of breeder reaction mechanism:

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• How a breeder reactor works?

It works by using highly enriched uranium between 15-20% uranium-235 content, surrounded or "blanketed" by natural uranium-238 in the reactor core. Neutrons released during this reaction are absorbed by a "blanket" of fertile uranium surrounding the core. Fertile uranium is harder to split than fissile uranium but turns into plutonium when it absorbs neutrons. Since fast neutrons are more efficient in converting U²³⁸ to Pu²³⁹, there is no need for a moderator to slow down the neutrons produced in the fission.

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Cadmium rods control the chain reaction in the blanketed core, contained in a primary vessel. Unlike conventional reactors that use water to transfer heat, a breeder uses liquid sodium. The sodium does not slow the neutrons like water, and high-energy neutrons are more readily absorbed by the fertile uranium to create plutonium. The sodium surrounding the core flows through a heat exchanger, a cluster of thin walled metal tubes, and transfers its energy to a separate stream of sodium. The heat then passes through a steam generator. The steam drives a turbine thus generates electricity.

Conversion factor or Breeding ratio:

It is defined as the ratio of the number of secondary fuel (Pu²³⁹) produced to the number of primary fuel atoms (U²³⁸) consumed. It is generally expected as 1.4 and achieved is 1.2. The time required for a breeder reactor to produce enough material to fuel a second reactor is called its doubling time (targeted as 10 years).

Advantages of Breeder Reactors:

• Uranium sources are increased by 100 times by using U²³⁸ instead of U²³⁵.
• Energy produced is of low cost due to ready availability of U²³⁸ (without enrichment).

Disadvantages of Breeder Reactors:

• Sodium explodes if exposed to air or water. Therefore, any leakage can be dangerous.
• The high energy neutron makes sodium radioactive.
• Difficult to control.
• Uranium sources are increased by 100 times by using U²³⁸ instead of U²³⁵.

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• Differences Between Nuclear Reactor and Breeder Reactor

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List of Nuclear Power Plants in India

Operational nuclear power plants in India

Planned power plants in India

Practice Quiz

Unit III:

 https://docs.google.com/forms/d/e/1FAIpQLScdR3OEzM-dCmYt5_UKQ4AX4znSLYBECqSB4zStIs9rSKCw5w/viewform?usp=sf_link

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Assignment

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Case Analysis

(Chernobyl nuclear reactor – accident)

• The Chernobyl accident in 1986 was the result of a flawed reactor design that was operated with inadequately trained personnel.
• The resulting steam explosion and fires released at least 5% of the radioactive reactor core into the environment, with the deposition of radioactive materials in many parts of Europe.
• Two Chernobyl plant workers died due to the explosion on the night of the accident, and a further 28 people died within a few weeks as a result of acute radiation syndrome.
• The United Nations Scientific Committee on the Effects of Atomic Radiation has concluded that, apart from some 6500 thyroid cancers (resulting in 15 fatalities), "there is no evidence of a major public health impact attributable to radiation exposure 20 years after the accident."
• Some 350,000 people were evacuated as a result of the accident, but resettlement of areas from which people were relocated is ongoing. 

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https://youtu.be/tFo_0eEt1IY

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Part-A Question and Answer

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Part-A Question and Answer

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Part-B Questions

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Supportive online certification courses

1. Energy, Environment, and Everyday Life ife

https://www.coursera.org/learn/energy-environment-life

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2. Non-Conventional energy resources

https://nptel.ac.in/courses/121/106/121106014/#

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3. Understanding Nuclear Energy

https://www.edx.org/course/understanding-nuclear-energy

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4. Introduction to solar cells (Coursera 5-week course)

https://www.coursera.org/learn/solar-cells

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5. Exploring Renewable Energy Schemes (Coursera 6-week course)

https://www.coursera.org/learn/exploring-renewable-energy

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� Real time Applications in day to day life and to Industry

1. Toyota Prius lithium-ion and nickel metal hydride batteries and Toyota Mirai fuel cell hydrogen.

https://youtu.be/-yfPpIZYEjI

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2. Breakthrough in renewable energy.

https://youtu.be/mmyrbKBZ6SU

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3. How Do Electric Vehicles Work?

https://www.youtube.com/watch?v=GHGXy_sjbgQ

4. Types of Electric Vehicles

https://www.youtube.com/watch?v=h5ysddrlXLw

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Energy sources and storage devices - Real-time application�

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Content beyond the syllabus

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1. Ni-Cad Battery

It is rechargeable secondary cell. It consists of cadmium anode and a highly oxidized nickel cathode that is usually described as the nickel(III) oxo-hydroxide, NiO(OH).

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Because the products of the discharge half-reactions are solids that adhere to the electrodes [Cd(OH)₂ and 2Ni(OH)₂], the overall reaction is readily reversed when the cell is recharged. Although NiCad cells are lightweight, rechargeable, and high capacity, they have certain disadvantages. For example, they tend to lose capacity quickly if not allowed to discharge fully before recharging, they do not store well for long periods when fully charged, and they present significant environmental and disposal problems because of the toxicity of cadmium.

Advantages:

• The Nickel-Cadmium cell has small size and high rate charge/discharge capacity, which makes it very useful.
• It has also very low internal resistance and wide temperature range (up to 70ºC)
• It produces a potential about 1.4 volt and has longer life than lead storage cell.

https://youtu.be/GMV_4U4wQfE

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Content beyond the syllabus

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Uses:

• These are used in electronic calculators, electronic flash units, transistors etc.
• Ni-Cd cells are widely used in medical instrumentation and in emergency lighting, toys etc.

Eco-friendly fuel cells in automobiles

Fuel cell vehicles use hydrogen gas to power an electric motor. Unlike conventional vehicles which run on gasoline or diesel, fuel cell cars and trucks combine hydrogen and oxygen to produce electricity, which runs a motor. Since they’re powered entirely by electricity, fuel cell vehicles are also considered as electric vehicles (“EVs”).

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1. Hydrogen gas from the tank feeds down a pipe to the positive terminal.�2. Oxygen from the air comes down a second pipe to the negative terminal.�3. The positive terminal is made of platinum. When hydrogen gas reach the catalyst, they split up into hydrogen ions and electrons.�4. The protons, being positively charged, are attracted to the negative terminal and travel through the electrolyte towards it. The electrolyte is a thin membrane made of a special polymer film and only the protons can pass through it.�5. The electrons, meanwhile, flow through the outer circuit.�6. As they do so, they power the electric motor that drives the car's wheels. Eventually, they arrive at the negative terminal too.�7. At the negative terminal, the protons and electrons recombine with oxygen from the air in a chemical reaction that produces water.�8. The water is given off from the exhaust pipe as water vapor or steam.

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Tesla's primary EV battery 

The technology involved is NCA (based on nickel-cobalt-aluminum oxide chemistry). Tesla’s new batteries will rely on innovations such as low-cobalt and cobalt-free battery chemistries, and the use of chemical additives, materials and coatings that will reduce internal stress and enable batteries to store more energy for longer periods, sources said.

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Lamborgini uses supercapacitor for its most powerful car

In the Sián, the supercapacitor provides enough power to the e-motor to deliver an extra 34 horsepower. Lamborghini uses this to smooth out acceleration, bridging the gaps in power delivery that occur when the mechanical transmission changes gear.

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Do it yourself

• Cut open the primary, alkaline (Duracell), Mobile batteris (wasted - Li ion batteries)
• Analyse the components

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Prescribed Text Books & Reference Books

• Textbooks
• P. C. Jain and Monika Jain, “Engineering Chemistry”, 17^th edition, Dhanpat Rai Publishing Company Pvt. Ltd., New Delhi, 2018.
• Prasanta Rath, “Engineering Chemistry”, Cengage Learning India Pvt. Ltd., Delhi, 2015.
• References
• S. S. Dara and S. S. Umare, “A Textbook of Engineering Chemistry”, S. Chand & Company, New Delhi, 2015.
• Kirpal Singh, “Chemistry in everyday life”, 3^rd edition, -PHI Learning Pvt. Ltd., 2012.
• J.C. Kuriacose and J.Rajaram, “Chemistry in Engineering and Technology”, Volume-1 & Volume -2, Tata McGraw-Hill Education Pvt. Ltd., 2001.
• Geoffrey A Ozin, Andre C Arsenault “Nanochemistry: A Chemical Approach to Nanomaterials”, 2^nd edition, RSC publishers, 2005.
• Prasanna Chandrasekhar, “Conducting polymers, fundamentals and applications A Practical Approach”, 1^st edition, Springer Science Business Media New York, 1999.

E-Content:

Engineering Chemistry - Fundamentals and Applications - Shikha Agarwal

https://www.pdfdrive.com/engineering-chemistry-fundamentals-and-applications-2nd-edition-d191456798.html

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Mini project suggestions

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Thank you