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FUEL CELL

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MINOR-2 ASINGNMENT

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content Introduction Fuel Cell Operation Hydrogen Fuel Cell Efficiency Parts of a Fuel Cell Working Advantages/Disadvantages of Fuel Cells Applications

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Introduction

What is fuel cell?A Fuel cell is a electrochemical device that converts chemical energy into

electrical energy.

Every fuel cell has two electrodes, one positive and one negative,called respectively, the cathode and anode. The reactions that produce electricity take place at the electrodes.

In all types of fuel cell, hydrogen is used as fuel and can be obtained from any source of hydrocarbon.

The fuel cell transform hydrogen and oxygen into electric power,emitting water as their only waste product.

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Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes.

A single fuel cell generates a tiny amount of direct current (DC) electricity.

A converter is used to produce AC current

In practice, many fuel cells are usually assembled into a stack. Cell or stack, the principles are the same.

In 1932, Francis Bacon developed the first successful FC. He used hydrogen, oxygen, an alkaline electrolyte, and nickel electrodes.

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Fuel Cell Operation

Pressurized hydrogen gas (H2) enters cell on anode side. Gas is forced through catalyst by pressure.

When H2 molecule comes contacts platinum catalyst, it splits into two H+ ions and two electrons (e-). Electrons are conducted through the anodeMake their way through the external circuit (doing useful work such as turning a motor) and return to the cathode side of the fuel cell.

On the cathode side, oxygen gas (O2) is forced through the catalystForms two oxygen atoms, each with a strong negative charge. Negative charge attracts the two H+ ions through the membrane, Combine with an oxygen atom and two electrons from the external circuit to form a water molecule (H2O).

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Hydrogen Fuel Cell Efficiency

1. 40% efficiency converting methanol to hydrogen in reformer. 2. 80% of hydrogen energy content converted to electrical energy.3. 80% efficiency for inverter/motor4. Converts electrical to mechanical energy5. Overall efficiency of 24-32%

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Parts of a Fuel Cell

AnodeNegative post of the fuel cell. Conducts the electrons that are freed from the hydrogen molecules so that they can be used in an external circuit. Etched channels disperse hydrogen gas over the surface of catalyst.CathodePositive post of the fuel cellEtched channels distribute oxygen to the surface of the catalyst.Conducts electrons back from the external circuit to the catalystRecombine with the hydrogen ions and oxygen to form water. ElectrolyteProton exchange membrane.Specially treated material, only conducts positively charged ions.Membrane blocks electrons. Catalyst Special material that facilitates reaction of oxygen and hydrogenUsually platinum powder very thinly coated onto carbon paper or cloth.Rough & porous maximizes surface area exposed to hydrogen or oxygenThe platinum-coated side of the catalyst faces the PEM.

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Working

The Fuel gas (hydrogen rich) is passed towards the anode where the following oxidation reaction occurs:

H2 (g) = 2H+ + 2e-

The liberated electrons from hydrogen in anode side do not migrate through electrolyte.

Therefore, they passes through the external circuit where work is performed, then finally goes into the cathode.

On the other hand, the positive hydrogen ions (H+) migrate across the electrolyte towards the cathode.

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At the cathode side the hydrogen atom reacts with oxygen gas (from air) and electrons to form water as byproduct according to:

The overall cell reaction isfuel + oxidant product + Heat

H2 + 1/2 O2 +2e- = H2O + Heat

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The liberated electrons from the hydrogen are responsible for the production of electricity. The water is produced by the combination of hydrogen, oxygen and liberated electrons and is sent out from the cell.

The DC current produced by fuel cell is later converted into AC current using an inverter for practical application.

The voltage developed in a single fuel cell various from 0.7 to 1.4 volt.More power can be obtained by arranging the individual fuel cell as a stack. In this case, each single cell is sandwiched with one another by a interconnect.

Therefore, electricity power ranging from 1 kW to 200 kW can be obtained for domestic as well as industrial application.

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Hydrogen Oxygen

Electrical power production by fuel cell

Rotating shaft connected to generator for electricity production

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Advantages/Disadvantages of Fuel Cells

• Zero Emissions: a fuel cell vehicle only emits water vapour. There fore, no air

pollution occurs.

• High efficiency: Fuel cells convert chemical energy directly into electricity without the combustion process.As a result, Fuel cells can achieve high efficiencies in energy conversion.

• High power density: A high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space

constraints.

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Applications 1. Portable applications

They used in portable appliances and power tools .

They can be used in small personal vehicles .

They are used Consumer electronics like laptops, cell phones can be operated.

They can be used in Backup power .

2. Transportation applications

They can be used for transport application in the following areas.

Industrial transportation.

Public transportation.

Commercial transportation (truck, tractors).

Marine and Military transportation.

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Power distribution application

• Fuel cells can be used for the distribution of power in various

fields such as,

• Homes and small businesses

• Commercial and industrial sites

• Remote, off-grid locations (telecom towers, weather stations)