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Renewable Energy Sources.

Fuel Cells

SJSU-E10

S-2008John Athanasiou

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What is A Fuel Cell?

• A fuel cell is an electrochemical energy conversion device.

• It produces electricity from external supplies of fuel (anode side) and oxidant (cathode side).

• A fuel cell is similar to a battery in that an electrochemical reaction is used to create electric current.

• Fuel cells are different from batteries in that they consume reactant, which must be replenished, while batteries store electrical energy chemically in a closed system.

• (Recall that Solar cells are not electrochemical)

R. Chang: Fuel_Cell_technology_F07

3http://www.greenjobs.com/Public/images/fuel-cell.jpg

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Fuel Cell Applications

• Fuel cells are very useful as power sources in remote locations, such as spacecraft, remote weather stations, large parks, rural locations, and in certain military applications.

• A fuel cell system running on hydrogen can be compact, lightweight and has 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.

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Toyota FCHV PEM FC fuel cell vehicle

A hydrogen fuel cell public bus accelerating at traffic lights in Perth, Western Australia

The world's first certified Fuel Cell Boat (HYDRA), Karl-Heine Kanal in Leipzig, Germany

Micro-fuel cell developed by Fraunise ISE for use in applications such as cellular phones

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• Fuel cells have as reactants gases (hydrogen and oxygen) that are combined in a catalytic process.

• Since the gas reactants can be fed into the fuel cell and constantly replenished, the unit will never run down like a battery.

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How does a fuel cell work?

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A fuel cell consists of an anode, cathode, and electrolyte

A fuel cell consists of two electrodes (an anode and a cathode) that sandwich an electrolyte (a specialized material that allows ions to pass but blocks electrons).

CA

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Solid Oxide Fuel Cells ( SOFCs )

A solid oxide fuel cell is a device that converts gaseous fuels

(hydrogen, natural gas, gasified coal) via an Electrochemical

process directly into electricity.

Air is supplied to the cathode (air electrode)

At the cathode, the O2 molecules are ionized

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In SOFCs oxygen ions react with H2 from the

fuel The ionized oxygen diffuses across the electrolyte

At the anode, the O2- ions react with H (in the fuel).

H2 + O2- H2O + 2e-

The reaction produces electrons to do work and water.

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SOFC -- passing oxygen ions across a solid

electrolyte.1. SOFC has a ceramic cathode that ionizes

oxygen. The cathode needs to be porous to allow air in.

2. The oxygen ions diffuse across a solid, dense, ceramic electrolyte.

3. At the anode, the oxygen ions react with hydrogen to form water and electrons.

4. The electrons can not flow through the electrolyte so they leave through the load.

Cath.Anod.

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• A typical cell running at 0.7 V has an efficiency of about 50%.• Therefore 50% of the energy content of the hydrogen is converted into electrical energy;

• The remaining 50% will be converted into

heat.

Fuel Cell Efficiency

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Fuel Cell Lab Exercise

Charging

Discha

rging

Mod

e

motor

Fuel cell

H2 tank

O2 tank

plug

Power meter

Prop up the front wheels

Discharging Mode

Distilled Water Syrin

ge

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Q1. The major difference between fuel cells and batteries is:

A. Fuel cells generate hydrogen gas, whereas batteries consume stored solid or liquid

B. Fuel cells generate oxygen gas, whereas batteries consume electricity

C. Fuel cells consume hydrogen gas, whereas batteries consume stored solid or liquid

D. Fuel cells consume oxygen gas, whereas batteries consume stored solid or liquid

E. Fuel cells consume water, whereas batteries consume stored solid or liquid

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Q2. Which of the following is the by-product of

a fuel cell reaction? A. Water

B. Hydrogen

C. Oxygen

D. Electrolyte

E. All of the above

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Q3. Which of the following is not a reactant of a fuel cell?

A. Bio-diesel

B. Methane

C. Methanol

D. Air

E. Gasoline

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Q4. Which of the following describes the function of a fuel cell in a discharge mode?

A. Air is supplied to the cathode side.

B. Air is supplied to the anode side.

C. Water is supplied to the cathode side.

D. Water is supplied to the anode side.

E. Hydrogen gas is supplied to the cathode side.