Battery and Fuel Cells Complete 12-11-2014

8/10/2019 Battery and Fuel Cells Complete 12-11-2014

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Batteries and Fuel Cells

Sahyadri Science College (A), Shimoga 1

BATTERY (ELECTRICITY)

An electric battery is a device consisting of one or

moreelectrochemical cells that convert stored chemical energy into

electrical energy. Each cell contains a positive terminal,

orcathode, and a negative terminal,

oranode.Electrolytes allow ions to move between the

electrodes and terminals, which allows current to flow out of

the battery to perform work.

Primary (single-use or "disposable") batteries are used once and discarded; the electrode

materials are irreversibly changed during discharge. Common examples are the alkaline battery

used forflashlights and a multitude of portable devices.Secondary (rechargeable batteries) can

be discharged and recharged multiple times; the original composition of the electrodes can be

restored by reverse current. Examples include the lead-acid batteries used in vehicles and lithium

ion batteries used for portable electronics. Batteries come in many shapes and sizes, from

miniature cells used to powerhearing aids and wristwatches to battery banks the size of rooms

that provide standby power fortelephone exchanges and computerdata centers.

History

Thesymbol for a battery in acircuit diagram.It originated as a schematic drawing of the

earliest type of battery, a voltaic pile. The usage of "battery" to describe a group electrical

devices dates toBenjamin Franklin,who in 1748 described multipleLeyden jarsby analogy to abattery
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of cannon (Benjamin Franklin borrowed the term "battery" from the military, which refers to weapons

functioning together).Alessandro Volta described the first electrochemical battery, thevoltaic pile in

1800.This was a stack of copper and zinc plates, separated by brine soaked paper disks that could produce

a steady current for a considerable length of time. Volta did not appreciate that the voltage was due to

chemical reactions. He thought that his cells were an inexhaustible source of energy, and that the

associated corrosion effects at the electrodes were a mere nuisance, rather than an unavoidable

consequence of their operation, asMichael Faraday showed in 1834.

Although early batteries were of great value for experimental purposes, in practice their

voltages fluctuated and they could not provide a large current for a sustained period. TheDaniel

cell,invented in 1836 by British chemistJohn Frederic Daniel,was the first practical source of

electricity, becoming an industry standard and seeing widespread adoption as a power source

forelectrical telegraph networks. It consisted of a copper pot filled with acopper

sulfate solution, in which was immersed an unglazedearthenware container filled withsulfuric

acid and a zinc electrode.

These wet cells used liquid electrolytes, which were prone to leakage and spillage if not

handled correctly. Many used glass jars to hold their components, which made them fragile.

These characteristics made wet cells unsuitable for portable appliances. Near the end of the

nineteenth century, the invention ofdry cell batteries,which replaced the liquid electrolyte with a

paste, made portable electrical devices practical.

Principle of Operation

A voltaic cell for demonstration purposes. In this example the two half-cells are linked by

asalt bridgeseparator that permits the transfer of ions.

Batteries convert chemical energy directly to electrical energy. A battery consists of some

number of voltaic cells. Each cell consists of twohalf-cells connected in series by a conductive
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electrolyte containing anions and cations. One half-cell includes electrolyte and the negative

ectrode, the electrode to whichanions (negatively charged ions) migrate; the other half-cell

includes electrolyte and the positive electrode to whichcations (positively charged ions)

migrate.Redox reactions power the battery. Cations are reduced (electrons are added) at the

cathode during charging, while anions are oxidized (electrons are removed) at the anode during

discharge. The electrodes do not touch each other, but are electrically connected by

theelectrolyte.Some cells use different electrolytes for each half-cell. A separator allows ions to

flow between half-cells, but prevents mixing of the electrolytes.

Categories and types of batteries

Batteries are classified into primary and secondary forms.

Primary batteries irreversibly transform chemical energy to electrical energy. When the

supply of reactants is exhausted, energy cannot be readily restored to the battery.

Secondary batteries can be recharged; that is, they can have their chemical reactions reversed

by supplying electrical energy to the cell, approximately restoring their original composition.

Primary batteries

Primary batteries, orprimary cells,can produce current immediately on assembly. These

are most commonly used in portable devices that have low current drain, are used only

intermittently, or are used well away from an alternative power source, such as in alarm and

communication circuits where other electric power is only intermittently available. Disposable

primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible

and active materials may not return to their original forms. Battery manufacturers recommend

against attempting to recharge primary cells.

In general, these have higherenergy densities than rechargeable batteries, but disposable

batteries do not fare well under high-drain applications withloads under 75ohms (75 ).

Common types of disposable batteries includezinccarbon batteries andalkaline batteries.

Secondary Batteries

Secondary batteries, also known assecondary cells, or rechargeable batteries, must be

charged before first use; they are usually assembled with active materials in the discharged state.
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Rechargeable batteries are (re)charged by applying electric current, which reverses the chemical

reactions that occur during discharge/use. Devices to supply the appropriate current are called

chargers.

The oldest form of rechargeable battery is theleadacid battery.This technology containsliquid electrolyte in an unsealed container, requiring that the battery be kept upright and the area

be well ventilated to ensure safe dispersal of thehydrogen gas it produces during overcharging.

The leadacid battery is relatively heavy for the amount of electrical energy it can supply. Its low

manufacturing cost and its high surge current levels make it common where its capacity (over

approximately 10 Ah) is more important than weight and handling issues. A common application

is the moderncar battery,which can, in general, deliver a peak current of 450amperes.

Battery cell types

Many types of electrochemical cells have been produced, with varying chemical

processes and designs, includinggalvanic cells,electrolytic cell,fuel cells,flow cells and voltaic

piles.

Wet cells

A wet cell battery has a liquidelectrolyte.Other names areflooded cell, since the liquid

covers all internal parts, or vented cell, since gases produced during operation can escape to the

air. Wet cells were a precursor to dry cells and are commonly used as a learning tool

forelectrochemistry. They can be built with common laboratory supplies, such asbeakers, for

demonstrations of how electrochemical cells work. A particular type of wet cell known as

aconcentration cell is important in understandingcorrosion.Wet cells may beprimary cells (non-

rechargeable) orsecondary cells (rechargeable). Originally, all practical primary batteries such as

theDaniel cell were built as open-top glass jar wet cells. Other primary wet cells are

theLeclanche cell,Grove cell,Bunsen cell,Chromic acid cell,Clark cell,andWeston cell.The

Leclanche cell chemistry was adapted to the first dry cells. Wet cells are still used inautomobile

batteries and in industry for standby power forswitchgear, telecommunication or

largeuninterruptible power supplies,but in many places batteries withgel cells have been used

instead. These applications commonly use leadacid ornickelcadmium cells.
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Dry cell

Line art drawing of a dry cell:

1. Brass cap, 2. plastic seal, 3. Expansion space, 4. Porous cardboard, 5. Zinc can, 6. Carbon rod,

7. Chemical mixture.

A dry cell uses a paste electrolyte, with only enough moisture to allow current to flow.

Unlike a wet cell, a dry cell can operate in any orientation without spilling, as it contains no free

liquid, making it suitable for portable equipment. By comparison, the first wet cells were

typically fragile glass containers with lead rods hanging from the open top and needed careful

handling to avoid spillage. Leadacid batteries did not achieve the safety and portability of the

dry cell until the development of thegel battery.

A common dry cell is thezinccarbon battery,sometimes called the dryLeclanch cell,

with a nominal voltage of 1.5volts, the same as thealkaline battery (since both use the

samezincmanganese dioxide combination).

A standard dry cell comprises azinc anode, usually in the form of a cylindrical pot, with

acarbon cathode in the form of a central rod. The electrolyte is ammonium chloride in the form

of a paste next to the zinc anode. The remaining space between the electrolyte and carbon

cathode is taken up by a second paste consisting of ammonium chloride and manganese dioxide,
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the latter acting as adepolariser. In some designs, the ammonium chloride is replaced byzinc

chloride.

Battery lifetime

Available capacity of all batteries drops with decreasing temperature. In contrast to most

of today's batteries, theZamboni pile,invented in 1812, offers a very long service life without

refurbishment or recharge, although it supplies current only in the nanoamp range. TheOxford

Electric Bell has been ringing almost continuously since 1840 on its original pair of batteries,

thought to be Zamboni piles.

Self-discharge

Disposable batteries typically lose 8 to 20 percent of their original charge per year when

stored at room temperature (2030 C). This is known as the "self-discharge" rate, and is due

to non-current-producing "side" chemical reactions that occur within the cell even when no load

is applied. The rate of side reactions is reduced for batteries are stored at lower temperatures,

although some can be damaged by freezing.

Old rechargeable batteries self-discharge more rapidly than disposable alkaline batteries,

especially nickel-based batteries; a freshly charged nickel cadmium (NiCd) battery loses 10% of

its charge in the first 24 hours, and thereafter discharges at a rate of about 10% a month.

However, newerlow self-discharge nickel metal hydride (NiMH) batteries and modern lithium

designs display a lower self-discharge rate (but still higher than for primary batteries).

Corrosion

Internal parts may corrode and fail, or the active materials may be slowly converted to

inactive forms.

Physical component changes
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The active material on the battery plateschanges chemical composition on each charge

and discharge cycle, active material may be lost due to physical changes of volume; further

limiting the number of times the battery can be recharged.

Rechargeable batteries

Most nickel-based batteries are partially discharged when purchased, and must be

charged before first use. Newer NiMH batteries are ready to be used when purchased, and have

only 15% discharge in a year. Some deterioration occurs on each chargedischarge cycle.

Degradation usually occurs because electrolyte migrates away from the electrodes or because

active material detaches from the electrodes.

Charge/discharge speed

Fast charging increases component changes, shortening battery lifespan.

Overcharging

If a charger cannot detect when the battery is fully charged then overcharging is likely,

damaging it.

Environmental conditions

Automotiveleadacid rechargeable batteries must endure stress due to vibration, shock,

and temperature range. Because of these stresses andsulfation of their lead plates, fewautomotive batteries last beyond six years of regular use. Automotive starting (SLI:Starting,

Lighting, Ignition) batteries have many thin plates to maximize current. In general, the thicker

the plates the longer the life. They are typically discharged only slightly before recharge.

"Deep-cycle" leadacid batteries such as those used in electric golf carts have much

thicker plates to extend longevity. The main benefit of the leadacid battery is its low cost; its

main drawbacks are large size and weight for a given capacity and voltage. Leadacid batteries

should never be discharged to below 20% of their capacity, because internal resistance willcause heat and damage when they are recharged. Deep-cycle leadacid systems often use a low-

charge warning light or a low-charge power cut-off switch to prevent the type of damage that

will shorten the battery's life.
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Storage

Battery life can be extended by storing the batteries at a low temperature, as in

arefrigerator orfreezer, which slows the side reactions. Such storage can extend the life of

alkaline batteries by about 5%; rechargeable batteries can hold their charge much longer,

depending upon type. To reach their maximum voltage, batteries must be returned to room

temperature; discharging an alkaline battery at 250 mA at 0 C is only half as efficient as at

20 C. Alkaline battery manufacturers such asDuracell do not recommend refrigerating

batteries.

Battery sizes

Primary batteries readily available to consumers range from tinybutton cells used for

electric watches, to the No. 6 cell used for signal circuits or other long duration applications.

Secondary cells are made in very large sizes; very large batteries can power asubmarine or

stabilize anelectrical grid and help level out peak loads.

Hazards:

Explosion

A battery explosion is caused by misuse or malfunction, such as attempting to recharge a

primary (non-rechargeable) battery, or ashort circuit.Car batteries are most likely to explodewhen a short-circuit generates very large currents. Car batteries producehydrogen, which is

very explosive, when they are overcharged (because ofelectrolysis of the water in the

electrolyte). The amount of overcharging is usually very small and generates little hydrogen,

which dissipates quickly. However, when "jumping" a car battery, the high current can cause

the rapid release of large volumes of hydrogen, which can be ignited explosively by a nearby

spark, for example, when disconnecting ajumper cable.

When a battery is recharged at an excessive rate, an explosive gas mixture of hydrogen

and oxygen may be produced faster than it can escape from within the battery, leading to

pressure build-up and eventual bursting of the battery case. In extreme cases, battery acid may

spray violently from the casing and cause injury. Overchargingthat is, attempting to charge a

battery beyond its electrical capacitycan also lead to a battery explosion, in addition to

leakage or irreversible damage. It may also cause damage to the charger or device in which the
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overcharged battery is later used. In addition, disposing of a battery via incineration may cause

an explosion as steam builds up within the sealed case.

Leakage

Leaked alkaline battery.

Many battery chemicals are corrosive, poisonous or both. If leakage occurs, either

spontaneously or through accident, the chemicals released may be dangerous.

For example, disposable batteries often use a zinc "can" both as a reactant and as the

container to hold the other reagents. If this kind of battery is over-discharged, the reagents can

emerge through the cardboard and plastic that form the remainder of the container. The active

chemical leakage can then damage the equipment that the batteries power. For this reason, many

electronic device manufacturers recommend removing the batteries from devices that will not

be used for extended periods of time.

Toxic materials

Many types of batteries employ toxic materials such as lead,mercury,andcadmium as an

electrode or electrolyte. When each battery reaches end of life it must be disposed of to prevent

environmental damage. Battery are one form ofelectronic waste (e-waste).E-

wasterecycling services recover toxic substances, which can then be used for new batteries. Of

the nearly three billion batteries purchased annually in the United States, about 179,000 tons

end up in landfills across the country.

Ingestion

Batteries may be harmful or fatal ifswallowed.Smallbutton cells can be swallowed, in

particular by young children. While in the digestive tract, the battery's electrical discharge may

lead to tissue damage; such damage is occasionally serious and can lead to death. Ingested disk
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batteries do not usually cause problems unless they become lodged in thegastrointestinal tract.

The most common place for disk batteries to become lodged is the esophagus, resulting in

clinical sequel. Batteries that successfully traverse the esophagus are unlikely to lodge

elsewhere. The likelihood that a disk battery will lodge in the esophagus is a function

of the patient's age and battery size. Disk batteries of 16 mm have become lodged in the

esophagi of 2 children younger than 1 year. Older children do not have problems with

batteries smaller than 2123 mm. Liquefaction necrosis may occur because sodium hydroxide is

generated by the current produced by the battery (usually at the anode). Perforation has occurred

as rapidly as 6 hours after ingestion.

Daniell cells are easy to make at home.Aluminiumair batteries can be produced with

high-purity aluminium.Aluminium foilbatteries will produce some electricity, but are notefficient, in part because a significant amount of (combustible)hydrogen gas is produced.
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Battery chemistry

Primary batteries and their characteristics

Chemistry

A

node(-)

Cathode

(+)

Maximum

Voltage

(Theoretical)

(V)

Working

Voltage

(Practical)

(V)

Specific

energy[MJ/kg]Elaboration

Shelf Life

at 25 C

(80%

Capacity)

(Months)

Zinccarbon Zn MnO2 1.6 1.2 0.13 Inexpensive. 18

Zincchloride 1.5Also known as "heavy-duty",

inexpensive.

Alkaline(zinc

manganese

dioxide)

Zn MnO2 1.5 1.15 0.40.59Moderate energy density.Good for high- and low-drain

uses.

30

Nickeloxyhydroxide

(zincmanganese

dioxide/nickeloxyhydroxide)

1.7Moderate energy density.Good for high drain uses.

Lithium

(lithium

copper oxide)LiCuO

1.7

No longer manufactured.

Replaced by silver oxide (IEC-type "SR") batteries.

Lithium

(lithiumiron

disulfide)LiFeS2

1.5

Expensive.

Used in 'plus' or 'extra'batteries.
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Chemistry

Anode(-)

Cathode

(+)

Maximum

Voltage

(Theoretical)

(V)

Working

Voltage

(Practical)

(V)

Specific

energy[MJ/kg]Elaboration

Shelf Life

at 25 C

(80%

Capacity)

(Months)

Lithium

(lithium

manganesedioxide)

LiMnO2

3.0 0.831.01

Expensive.Used only in high-drain devices

or for long shelf-life due to

very low rate of self-discharge.'Lithium' alone usually refers to

this type of chemistry.

Lithium(lithium

chromiumoxide)

LiCrO2

Li CrO2 3.8 3.0 108

Mercuryoxide

Zn HgO 1.34 1.2

High-drain and constant

voltage.Banned in most countries

because of health concerns.

36

Zincair Zn O2 1.6 1.1 1.59 Used mostly in hearing aids.

Silver-oxide (silver

zinc)

Zn Ag2O 1.85 1.5 0.47Very expensive.Used only commercially in

'button' cells.

30

Magnesium Mg MnO2 2.0 1.5 40
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Homemade Cells

Almost any liquid or moist object that has enough ions to be electrically

conductive can serve as the electrolyte for a cell. As a novelty or science demonstration, it is

possible to insert two electrodes made of different metals into alemon,potato, etc. and generatesmall amounts of electricity. "Two-potato clocks" are also widely available in hobby and toy

stores; they consist of a pair of cells, each consisting of a potato (lemon, et cetera)

with two electrodes inserted into it, wired in series to form a battery with enough

voltage to power a digital clock. Homemade cells of this kind are of no practical use.

Sony has developed abiological battery that generates electricity from sugar in a way that

is similar to the processes observed in living organisms. The battery generates electricity

through the use of enzymes that break down carbohydrates.

Lead acid cells can easily be manufactured at home, but a tedious charge/discharge cycle

is needed to 'form' the plates. This is a process in which lead sulfate forms on the plates, and

during charge is converted to lead dioxide (positive plate) and pure lead (negative plate).

Repeating this process results in a microscopically rough surface, increasing the surface area.

This increases the current the cell can deliver. For an example, see.
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Fuel cell

A. Direct-methanol fuel cell B. Scheme of a proton-conducting fuel cell.

A fuel cell is a device that converts the from afuel intoelectricity through a chemical

reaction withoxygen or another oxidizing agent. Hydrogenproduced from the

steammethane reforming ofnatural gas is the most common fuel, but for greater efficiency

hydrocarbons can be used directly such as natural gas and alcohols like methanol.Fuel cells are

different frombatteries in that they require a continuous source of fuel and oxygen/air to sustain

the chemical reaction whereas in a battery the chemicals present in the battery react with each

other to generate anelectromotive force (emf). Fuel cells can produce electricity continuously for

as long as these inputs are supplied.

The first fuel cells were invented in 1838. The first commercial use of fuel cells came

more than a century later inNASA space programs to generate power for probes, satellites and

space capsules. Since then, fuel cells have been used in many other applications. Fuel cells areused for primary and backup power for commercial, industrial and residential buildings and in

remote or inaccessible areas. They are also used to powerfuel-cell vehicles,including forklifts,

automobiles, buses, boats, motorcycles and submarines.
http://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Methanolhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Fuel-cell_vehiclehttp://en.wikipedia.org/wiki/File:Solid_oxide_fuel_cell_protonic.svghttp://en.wikipedia.org/wiki/File:Fuel_cell_NASA_p48600ac.jpghttp://en.wikipedia.org/wiki/File:Solid_oxide_fuel_cell_protonic.svghttp://en.wikipedia.org/wiki/File:Fuel_cell_NASA_p48600ac.jpghttp://en.wikipedia.org/wiki/Fuel-cell_vehiclehttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Methanolhttp://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Fuel


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History

Sketch of William Grove's 1839 fuel cell

The first references to hydrogen fuel cells appeared in 1838. In a letter dated October

1838 but published in the December 1838 edition of The London and Edinburgh Philosophical

Magazine and Journal of Science, Welsh physicist and barristerWilliam Grove wrote about the

development of his first crude fuel cells. He used a combination of sheet iron, copper and

porcelain plates, and a solution of sulphate of copper and dilute acid. In a letter to the same

publication written in December 1838 but published in June 1839, German physicistChristian

Friedrich Schnbein discussed the first crude fuel cell that he had invented. His letter discussed

current generated from hydrogen and oxygen dissolved in water. Grove later sketched his design,

in 1842, in the same journal. The fuel cell he made used similar materials to today'sphosphoric-

acid fuel cell.

In 1939, British engineerFrancis Thomas Bacon successfully developed a 5 kW

stationary fuel cell. UTC Power was the first company to manufacture and commercialize a

large, stationary fuel cell system for use as aco-generationpower plant in hospitals, universities

and large office buildings.[12]

UTC Power continues to be the sole supplier of fuel cells to NASA

for use in space vehicles, having supplied fuel cells for theApollo missions,[13]

and theSpace

Shuttle program,and is developing fuel cells for cell phone towers and other applications.
http://en.wikipedia.org/wiki/William_Robert_Grovehttp://en.wikipedia.org/wiki/Christian_Friedrich_Sch%C3%B6nbeinhttp://en.wikipedia.org/wiki/Christian_Friedrich_Sch%C3%B6nbeinhttp://en.wikipedia.org/wiki/Phosphoric-acid_fuel_cellhttp://en.wikipedia.org/wiki/Phosphoric-acid_fuel_cellhttp://en.wikipedia.org/wiki/Francis_Thomas_Baconhttp://en.wikipedia.org/wiki/UTC_Powerhttp://en.wikipedia.org/wiki/Co-generationhttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-12http://en.wikipedia.org/wiki/Fuel_cell#cite_note-12http://en.wikipedia.org/wiki/Fuel_cell#cite_note-12http://en.wikipedia.org/wiki/Apollo_missionhttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-13http://en.wikipedia.org/wiki/Fuel_cell#cite_note-13http://en.wikipedia.org/wiki/Fuel_cell#cite_note-13http://en.wikipedia.org/wiki/Space_Shuttle_programhttp://en.wikipedia.org/wiki/Space_Shuttle_programhttp://en.wikipedia.org/wiki/File:1839_William_Grove_Fuel_Cell.jpghttp://en.wikipedia.org/wiki/Space_Shuttle_programhttp://en.wikipedia.org/wiki/Space_Shuttle_programhttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-13http://en.wikipedia.org/wiki/Apollo_missionhttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-12http://en.wikipedia.org/wiki/Co-generationhttp://en.wikipedia.org/wiki/UTC_Powerhttp://en.wikipedia.org/wiki/Francis_Thomas_Baconhttp://en.wikipedia.org/wiki/Phosphoric-acid_fuel_cellhttp://en.wikipedia.org/wiki/Phosphoric-acid_fuel_cellhttp://en.wikipedia.org/wiki/Christian_Friedrich_Sch%C3%B6nbeinhttp://en.wikipedia.org/wiki/Christian_Friedrich_Sch%C3%B6nbeinhttp://en.wikipedia.org/wiki/William_Robert_Grove


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Types of Fuel Cells

Fuel cells come in many varieties; however, they all work in the same general manner.

They are made up of three adjacent segments: theanode, theelectrolyte,and thecathode.Two

chemical reactions occur at the interfaces of the three different segments. The net result of the

two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current

is created, which can be used to power electrical devices, normally referred to as the load.

At the anode acatalyst oxidizes the fuel, usually hydrogen, turning the fuel into a

positively charged ion and a negatively charged electron. The electrolyte is a substance

specifically designed so ions can pass through it, but the electrons cannot. The freed electrons

travel through a wire creating the electric current. The ions travel through the electrolyte to the

cathode. Once reaching the cathode, the ions are reunited with the electrons and the two reactwith a third chemical, usually oxygen, to create water or carbon dioxide.

A block diagram of a fuel cell

The most important design features in a fuel cell are,

The electrolyte substance. The electrolyte substance usually defines the type of fuel cell.

The fuel that is used. The most common fuel is hydrogen.

The anode catalyst breaks down the fuel into electrons and ions. The anode catalyst is

usually made up of very fine platinum powder.
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The cathode catalyst turns the ions into the waste chemicals like water or carbon dioxide.

The cathode catalyst is often made up of nickel but it can also be a nanomaterial-based

catalyst.

Voltage decreases as current increases, due to several factors :

Activation loss

Ohmic loss (voltage drop due to resistance of the cell components and interconnections)

Mass transport loss (depletion of reactants at catalyst sites under high loads, causing rapid

loss of voltage).

To deliver the desired amount of energy, the fuel cells can be combined inseries to yield

highervoltage,and in parallel to allow a highercurrent to be supplied. Such a design is called

a fuel cell stack. The cell surface area can also be increased, to allow higher current from each

cell. Within the stack, reactant gases must be distributed uniformly over each of the cells to

maximize the power output.

1) Proton exchange membrane fuel cells (PEMFCs)

In the archetypical hydrogenoxideproton exchange membrane fuel cell design, a proton

conducting polymer membrane (theelectrolyte)separates theanode andcathode sides. This was

called a "solid polymer electrolyte fuel cell" (SPEFC) in the early 1970s, before the proton

exchange mechanism was well-understood. (Notice that the synonyms "polymer electrolyte

membrane" and "proton exchange mechanism" result in the sameacronym.)

On the anode side, hydrogen diffuses to the anode catalyst where it later dissociates into

protons and electrons. These protons often react with oxidants causing them to become what are

commonly referred to as multi-facilitated proton membranes. The protons are conducted through

the membrane to the cathode, but the electrons are forced to travel in an external circuit

(supplying power) because the membrane is electrically insulating. On the cathode catalyst,

oxygenmolecules react with the electrons (which have traveled through the external circuit) and

protons to form water.

In addition to this pure hydrogen type, there arehydrocarbon fuels for fuel cells,

includingdiesel,methanol (see:direct-methanol fuel cells and indirect methanol fuel cells) and
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chemical hydrides. The waste products with these types of fuel arecarbon dioxide and water,

when hydrogen is used the CO2 is released when methane from natural gas is combined with

steam in a process calledsteam methane reforming to produce the hydrogen, this can take place

in a different location to the fuel cell potentially allowing the hydrogen fuel cell to be used

indoors for example in fork lifts.

Construction of a high-temperaturePEMFC:Bipolar plate aselectrode with in-milled gas

channel structure, fabricated from conductivecomposites (enhanced withgraphite,carbon

black,carbon fiber, and/orcarbon nanotubes for more conductivity);Porous carbon papers;

reactive layer, usually on thepolymer membrane applied; polymer membrane.Condensation of

water produced by a PEMFC on the air channel wall. The gold wire around the cell ensures the

collection of electric current.

The different components of a PEMFC are;

1.bipolar plates,

2. electrodes,

3. catalyst,

4. membrane, and

5. The necessary hardware.

The materials used for different parts of the fuel cells differ by type. The bipolar plates may

be made of different types of materials, such as, metal, coated metal,graphite,flexible graphite,

CCcomposite, carbonpolymer composites etc. The membrane electrode assembly (MEA) is

referred as the heart of the PEMFC and is usually made of a proton exchange membrane

sandwiched between twocatalyst-coatedcarbon papers. Platinum and/or similar type ofnoble

metals are usually used as the catalyst for PEMFC. The electrolyte could be a

polymermembrane.
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2) Phosphoric acid fuel cell (PAFC)

Phosphoric acid fuel cells (PAFC) were first designed and introduced in 1961 byG. V.

Elmore andH. A. Tanner.In these cells phosphoric acid is used as a non-conductive electrolyte

to pass positive hydrogen ions from the anode to the cathode. These cells commonly work in

temperatures of 150 to 200 degrees Celsius. This high temperature will cause heat and energy

loss if the heat is not removed and used properly. This heat can be used to produce steam for air

conditioning systems or any other thermal energy consuming system. Using this heat

incogeneration can enhance the efficiency of phosphoric acid fuel cells from 4050% to about

80%. Phosphoric acid, the electrolyte used in PAFCs, is a non-conductive liquid acid which

forces electrons to travel from anode to cathode through an external electrical circuit. Since the

hydrogen ion production rate on the anode is small, platinum is used as catalyst to increase thisionization rate. A key disadvantage of these cells is the use of an acidic electrolyte. This

increases the corrosion or oxidation of components exposed to phosphoric acid.

3) High-temperature fuel cells

Solid Oxide Fuel Cell(SOFC):

A type of fuel cell in which the electrolyte is a solid, nonporous metal oxide, typically

zirconium oxide (ZrO2) treated with Y2O3, and O2is transported from the cathode to the anode.

Any CO in the reformate gas is oxidized to CO2 at the anode. Temperatures of operation are

typically 8001,000 C.

SOFCs are unique in that negatively charged oxygenions travel from

thecathode (positive side of the fuel cell) to theanode (negative side of the fuel cell) instead of

positively charged hydrogen ions travelling from the anode to the cathode, as is the case in all

other types of fuel cells. Oxygen gas is fed through the cathode, where it absorbs electrons to

create oxygen ions. The oxygen ions then travel through the electrolyte to react with hydrogen

gas at the anode. The reaction at the anode produces electricity and water as by-products. Carbon

dioxide may also be a by-product depending on the fuel, but the carbon emissions from an SOFC

system are less than those from a fossil fuel combustion plant. The chemical reactions for the

SOFC system can be expressed as follows:
http://en.wikipedia.org/w/index.php?title=G._V._Elmore&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=G._V._Elmore&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=H._A._Tanner&action=edit&redlink=1http://en.wikipedia.org/wiki/Cogenerationhttp://en.wikipedia.org/wiki/Solid_Oxide_Fuel_Cellhttp://en.wikipedia.org/wiki/Solid_Oxide_Fuel_Cellhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Solid_Oxide_Fuel_Cellhttp://en.wikipedia.org/wiki/Cogenerationhttp://en.wikipedia.org/w/index.php?title=H._A._Tanner&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=G._V._Elmore&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=G._V._Elmore&action=edit&redlink=1


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Anode Reaction: 2H2+ 2O2

2H2O + 4e

Cathode Reaction: O2+ 4e

2O2

Overall Cell Reaction: 2H2+ O2 2H2O

SOFC systems can run on fuels other than pure hydrogen gas. However, since hydrogen

is necessary for the reactions listed above, the fuel selected must contain hydrogen atoms. For

the fuel cell to operate, the fuel must be converted into pure hydrogen gas. SOFCs are capable

of internallyreforming light hydrocarbons such asmethane (natural gas), propane and

butane. These fuel cells are at an early stage of development.

Challenges exist in SOFC systems due to their high operating temperatures. One such

challenge is the potential for carbon dust to build up on the anode, which slows down the

internal reforming process.

Molten Carbonate Fuel Cell (MCFC):

Molten carbonate fuel cells (MCFCs) require a high operating temperature, 650 C

(1,200 F), similar toSOFCs. MCFCs use lithium potassium carbonate salt as an electrolyte,

and this salt liquefies at high temperatures, allowing for the movement of charge within the cell

in this case, negative carbonate ions.

Like SOFCs, MCFCs are capable of converting fossil fuel to a hydrogen-rich gas in the

anode, eliminating the need to produce hydrogen externally. The reforming process creates CO

2 emissions. MCFC-compatible fuels include natural gas, biogas and gas produced from coal.

The hydrogen in the gas reacts with carbonate ions from the electrolyte to produce water,

carbon dioxide, electrons and small amounts of other chemicals. The electrons travel through an

external circuit creating electricity and return to the cathode. There, oxygen from the air and

carbon dioxide recycled from the anode react with the electrons to form carbonate ions that

replenish the electrolyte, completing the circuit. The chemical reactions for an MCFC system

can be expressed as follows:

Anode Reaction: CO32+ H2 H2O + CO2+ 2e

Cathode Reaction: CO2+ O2+ 2e CO3

2

Overall Cell Reaction: H2+ O2 H2O

As with SOFCs, MCFC disadvantages include slow start-up times because of their high

operating temperature. This makes MCFC systems not suitable for mobile applications, and this
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more quickly or at a lower temperature. In a fuel cell, the catalyst facilitates the reaction of

oxygen and hydrogen. It is usually made of platinum powder very thinly coated onto carbon

paper or cloth. The catalyst is rough and porous so the maximum surface area of the platinum

can be exposed to the hydrogen or oxygen. The platinum-coated side of the catalyst faces the

membrane in the fuel cell.

Cathode:The electrode at which reduction (a gain of electrons) occurs. For fuel cells and other

galvanic cells, the cathode is the positive terminal; for electrolytic cells (where electrolysis

occurs), the cathode is the negative terminal.

Electrolyte:A substance that conducts charged ions from one electrode to the other in a fuel

cell, battery, or electrolyzer.

Membrane:The separating layer in a fuel cell that acts as electrolyte (an ion-exchanger) as well

as a barrier film separating the gases in the anode and cathode compartments of the fuel cell.

Polymer Electrolyte Membrane (PEM):A fuel cell incorporating a solid polymer membrane

used as its electrolyte. Protons (H+) are transported from the anode to the cathode. The operating

temperature range is generally 60100 C.

Solution:a: an act or the process by which a solid, liquid, or gaseous substance is

homogeneously mixed with a liquid or sometimes a gas or solid, b : a homogeneous mixture

formed by this process; especially : a single-phase liquid system, c : the condition of being

dissolved

Theoretical maximum efficiency

The energy efficiency of a system or device that converts energy is measured by the ratio

of the amount of useful energy put out by the system ("output energy") to the total amount of

energy that is put in ("input energy") or by useful output energy as a percentage of the total input

energy. In the case of fuel cells, useful output energy is measured inelectrical energyproduced

by the system. Input energy is the energy stored in the fuel. According to the U.S. Department of

Energy, fuel cells are generally between 4060% energy efficient. This is higher than some other
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systems for energy generation. For example, the typical internal combustion engine of a car is

about 25% energy efficient. In combined heat and power (CHP) systems, the heat produced by

the fuel cell is captured and put to use, increasing the efficiency of the system to up to 8590%.

The theoretical maximum efficiency of any type of power generation system is neverreached in practice, and it does not consider other steps in power generation, such as production,

transportation and storage of fuel and conversion of the electricity into mechanical power.

However, this calculation allows the comparison of different types of power generation. The

maximum theoretical energy efficiency of a fuel cell is 83%, operating at low power density and

using pure hydrogen and oxygen as reactants (assuming no heat recapture).

According to the World Energy Council, this compares with a maximum theoretical

efficiency of 58% for internal combustion engines. While these efficiencies are not approached

in most real world applications, high-temperature fuel cells (solid oxide fuel cells ormolten

carbonate fuel cells) can theoretically be combined with gas turbines to allow stationary fuel

cells to come closer to the theoretical limit. A gas turbine would capture heat from the fuel cell

and turn it into mechanical energy to increase the fuel cell's operational efficiency. This solution

has been predicted to increase total efficiency to as much as 70%.

Applications

Power

Stationary fuel cells are used for commercial, industrial and residential primary and

backup power generation. Fuel cells are very useful as power sources in remote locations, such

as spacecraft, remote weather stations, large parks, communications centers, rural locations

including research stations, and in certain military applications. A fuel cell system running on

hydrogen can be compact and lightweight, and have no major moving parts. Because fuel cells

have no moving parts and do not involve combustion, in ideal conditions they can achieve up to

99.9999% reliability. This equates to less than one minute of downtime in a six-year period.

Fuel cells can be used with low-quality gas from landfills or waste-water treatment plants

to generate power and lower methane emissions. A 2.8 MW fuel cell plant in California is said to

be the largest of the type.
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Cogeneration

Combined heat and power (CHP) fuel cell systems, includingMicro combined heat and

power (MicroCHP) systems are used to generate both electricity and heat for homes (seehome

fuel cell), office building and factories. The system generates constant electric power (selling

excess power back to the grid when it is not consumed), and at the same time produces hot air

and water from thewaste heat.As the result CHP systems have the potential to save primary

energy as they can make use of waste heat which is generally rejected by thermal energy

conversion systems.

The waste heat from fuel cells can be diverted during the summer directly into the ground

providing further cooling while the waste heat during winter can be pumped directly into the

building. The University of Minnesota owns the patent rights to this type of system

Fuel cell electric vehicles (FCEVs)

TheToyota FCV concept,unveiled at the 2013Tokyo Motor Show,is a practical concept

of thehydrogen fuel cell vehicle Toyota plans to launch around 2015.

Element One fuel cell vehicle.
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Automobiles

Although there are currently nofuel cell vehicles available for commercial sale, over 20

fuel cell electric vehicle (FCEV) prototypes and demonstration cars have been released since

2009.

Despite this, several major car manufacturers have announced plans to introduce a

production model of a fuel cell car in 2015. TheObama Administration sought to reduce funding

for the development of fuel cell vehicles, concluding that other vehicle technologies will lead to

quicker reduction in emissions in a shorter time.

Buses

Toyota FCHV-BUS at theExpo 2005

Notable Projects Include:

12 Fuel cell buses are being deployed in the Oakland and San Francisco Bay area of

California.

Daimler AG,with thirty-six experimental buses powered byBallard Power Systems fuel

cells completed a successful three-year trial, in eleven cities, in January 2007.

Airplanes

Boeing researchers and industry partners throughout Europe conducted experimental

flight tests in February 2008 of a manned airplane powered only by a fuel cell and lightweightbatteries. The fuel cell demonstrator airplane, as it was called, used a proton exchange membrane

(PEM) fuel cell/lithium-ion battery hybrid system to power an electric motor, which was coupled

to a conventional propeller. In 2003, the world's first propeller-driven airplane to be powered

entirely by a fuel cell was flown. The fuel cell was a unique Flat Stack design, which allowed the

fuel cell to be integrated with the aerodynamic surfaces of the plane.
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Boats

The world's first certified Fuel Cell Boat (HYDRA), in Germany

The world's first fuel-cell boatHYDRA used an AFC system with 6.5 kW net output.

Iceland has committed to converting its vast fishing fleet to use fuel cells to provide auxiliary

power by 2015 and, eventually, to provide primary power in its boats. Amsterdam recently

introduced its first fuel-cell-powered boat that ferries people around the city's famous and

beautiful canals.

Submarines

The Type 212 submarines of the German and Italian navies use fuel cells to remain

submerged for weeks without the need to surface.

Type 212 submarine with fuel cell propulsion of theGerman Navy in dry dock

The U212A is a non-nuclear submarine developed by German naval shipyard

Howaldtswerke Deutsche Werft. The system consists of nine PEM fuel cells, providing between30 kW and 50 kW each. The ship is silent giving it an advantage in the detection of other

submarines. A Recent naval paper has theorized about the the possibility of a Nuclear-Fuel Cell

Hybrid whereby the fuel cell is used when silent operations are required and then replenished

from the Nuclear reactor (and water). Such a system could potentially give a submarine weeks of
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stealth capability at a time with the endurance of a Nuclear reactor. It is not known if any such

submarines have been built.

Other applications

Providing power forbase stations orcell sites

Distributed generation

Emergency power systems are a type of fuel cell system, which may include lighting,

generators and other apparatus, to provide backup resources in a crisis or when regular

systems fail. They find uses in a wide variety of settings from residential homes to

hospitals, scientific laboratories,and data centers.

Telecommunication equipment and modern naval ships.

Base load power plants

Solar Hydrogen Fuel Cell Water Heating

Hybrid vehicles,pairing the fuel cell with either an ICE or a battery.

Notebook computers for applications whereAC charging may not be readily available.

Portable charging docks for small electronics

Smartphones,laptops and tablets.

Small heating appliances
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REFERENCES

1.

Engineering ChemistryVijay

2.

Advanced Physical Chemistry- Gurudeep Raj

3.

Physical Chemistry-Puri Sharma

4. Physical Chemistry-Pathaniya

5.

Understanding Batteries - R M Dell, David Antony

6. College Chemistry

7.

DiagramsWikipedia

8.

Material ScienceKurmi R S

Documents

Battery and Fuel Cells Complete 12-11-2014