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Copy of Hydrogen Fuel Cells

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sonia az

on 22 April 2014

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Transcript of Copy of Hydrogen Fuel Cells

HYDR GEN
"is the future.....but when is the future"
FUEL CELLS
F
uel

C
ells
Fuel Cells are basically electrochemical devices which produce electricity, from the conversion of fuel (hydrogen or oxygen) into electricity. Generally, a fuel cell does not store electricity, it is only a converter. Just like a car engine converts chemical energy into kinetic energy, this pretty much does the same, but converts it into electrical energy. There are many types of fuel cells, such as
:

Alkaline Fuel Cell
Molten Carbonate Fuel Cells
Phosphoric Acid Fuel Cells
Polymer Electrolyte Membrane Fuel Cell
Solid Oxide Fuel Cell
Direct Methanol Fuel Cell

However they all share the same basic material, such as solution or liquid, and hydrogen.
Electric Energy
+ HYDROGEN
F
UEL
C
ELLS
=
Now...
ELECTRICITY
Hydrogen
Fuel Cells
Alkaline Fuel Cell
Molten Carbonate
Fuel Cell
One of the very first fuel cells made, and used. It was used by NASA for spacecrafts, to produce water and electricity. About 60% of space related technology uses these fuel cells. This type of fuel cell uses Potassium Hydroxide as their electrolyte. In addition, it has the ability of using other catalysts at the anode and cathodes which are not precious, unlike platinum. It can operate at as low as 23°C to 70°C (for newer designs) . It only down side, is that is could be poisoned by CO2 , even if it was a small amount. As a result, if this happens the oxygen and hydrogen in the cell have to be purified, which costs a lot of money. And even if they are purified, the cell’s lifetime just decreased a lot. This fuel cells aren’t in a good place to compete with the mainstream commercial markets, since it only has a lifetime of about 8,000 operating hours. And most competing technologies which are used in large-scale application can go up to 40,000 hours.
The main design features of all fuel cells are :
The electrolyte, used for transportation of ions.
The fuel used, most of the time is hydrogen.
Anode Catalyst, which breaks the hydrogen into electrons and ions.
Cathode Catalyst, which changes ion to waste products. (in our case H2O and heat).
This fuel cell is designed for large scale application only, due to its conditions. These fuel cells are high-temperature, which use an electrolyte made up of molten carbonate salt. Temperatures can go above 650°C, which is why it isn’t meant for normal use. However, these high temperature can be harvest and used for the same reason! , generating electricity. The high temperatures can generate steam, which can turn turbines, which in return can produce electricity from kinetic energy.About 85% heat efficient, meaning that the heat produced and 85% of it was used. This type of fuel cell doesn’t require precious metal to be used for it to operate, therefore, reducing cost. The major difference from other fuel cells, is that it doesn’t require an external reformer for hydrogen. Due to high operating temperatures, the MCFC (molten carbonate fuel cell) has one built in.
H2 + CO3= = H2O + CO2 + 2e-
Proton Exchange
Membrane Fuel Cell
Also known as Polymer Electrolyte Membrane Fuel Cell.One of the most popular fuel cell today! It is used and being developed for transportation means. It uses a polymer which is a proton conducting membrane, such as perfluorosulfonic acid polymer as the electrolyte. This polymer is porous, meaning it can pass solutions across. It has two electrodes, which are the polymer. On the other side of the electrode, is a coat of hydrophobic compound such as Teflon, which forms a wet proof coating. This help provide a gas diffusion path to the catalyst layer. At the anode, H2 gets strip of from its electrons. The protons can pass through the polymer, but the electrons can’t. This forces the electrons to go through the anode to an external circuit, which it powers, then come back to the cathode to meet up with the proton of H. The products of this reaction are H2O, and heat.
H2 = 2H+ + 2e-
At Anode
At Cathode
1/2 O2 + 2H+ + 2e- = H2O
Career in Hydrogen Fuel Cell
Project Engineer
Fuel Cell Product Development Engineers
Mechanical Design Technologist
Polymer/Fuel-Cell R & D Engineer
Fuel Cell Designer Job
Fuel Cell Systems Engineer
Fuel Cell Development Engineer
The End
History of
F
uel
C
ells !

Sir William Grove
Francis Bacon
In the late
's
N
A
S
A
needed a compact way to generate electricity for space missions like

APOLLO 13
What is
F
UEL
C
ELL?
Fuel Cells are electrochemical devices that uses Hydrogen (H2) together with Oxygen from air to produce
electricity
and
Heat
.
The Working Principle of
FC

The basic physical structure of a single cell consists of an electrolyte layer in contact with a porous anode
(-ve)
and cathode
(+ve)
on either side.
In a typical
f
uel
c
ell, gaseous fuels are fed continuously to the anode and an oxidant (i.e., oxygen from air) is fed continuously to the cathode compartment; the electrochemical reactions take place at the electrodes to produce an electric current.
The Electrochemical Reactions :
Anodic reaction: H2
2H + 2e
-
Cathodic reaction: 1/2
2
O
+ 2H +2e
+
-
H2O
Overall reaction: H2 + 1/2 H2O + heat
O
2
Types of
F
uel
C
ells :
Alkaline Fuel Cell (AFC)
Molten Carbonate Fuel Cells (MCFC)
Phosphoric Acid Fuel Cells (PAFC)
Polymer Electrolyte Membrane Fuel Cell (PEM)
Solid Oxide Fuel Cell (SOFC)
Direct Methanol Fuel Cell (DMFC)
Advantages
Disadvantages
High Efficiency
Low Emissions
Fuel Flexibility
Low Maintenance
Very Expensive
Some technical problems
Still under Development
H
ydrogen
H
ydrogen is the true working reactant to reduce agent being oxidized in the current producing reaction at the anode of most types of fuel cells.
- Theoretically: .03 kg of hydrogen (at pressure of 1 bar and 25°C) is needed to produce 1 kWh of electrical energy.
- Practically: 0.046 kg is needed to produce 1kWH.

Problems of using
H
ydrogen:
1-
H
ydrogen is not natural fuel
2-
H
ydrogen is rather complicated in its storage, and transport.


1-
Finding ways to convert natural fuels to hydrogen and to carbon monoxide.
2-
Finding chemical ways to produce hydrogen under conditions convenient for fuel cell–powered autonomous power plants.
3-
ways to purify hydrogen and carbon monoxide obtained as in targets 1 and 2, so as to be fit to be used in the various types of fuel cells.
4-
Finding ways for convenient handling, storage, and transport of hydrogen.
Several points are important for the development and spread of fuel cells:
1-
Compressed
H
ydrogen: best way to storage
and transport
2-
Liquefied
H
ydrogen: mainly used in U.S
space shuttles
3-
Metal Hydrides: Alloys containing rare earth metals such as alloy LiN5 able to Expulsion and Absorption Hydrogen.
Ways to storage and transport
H
ydrogen used in fuel cell:
Membranes
1-
preventing any direct electronic contact between the electrodes
2-
provides ionic contact between these electrodes
Have two functions:

High ionic conductivity.

Lack of electronic conduction.

High mechanical stability.

High chemical stability and heat resistance under the operating conditions of a fuel cell.

Availability and acceptable cost.

Convenient handling during fuel cell assembly.
Basic requirements to do these functions:
The most commonly used types of membranes is Nafion proton-conducting
1-
Proton conductivity and mechanical properties
2-
Cannot be used at temperatures higher than 130-150℃
3-
High permeability of methanol
4-
Deterioration that occurs to it during the time
5-
Very sensitive to heavy metal ions
The disadvantage of this type:
Stationary Power Plants

Two kinds of stationary power plants:
1- Large:
(more than 10 kW)
2- small:
(less than 10 kW)
Large
power plants are used for (Power production) and (Heat supply) for customers in nearby places.
Examples Of Large Stationary Power Plants In Real Life:
- The UTC American company: 200kW units using PAFCEs
-In JAPAN: Multimegawatt power plants
-The US company Fuel-Cell Energy: 2mW power plant using MCFCs in Santa Clara.
Hybrid power plants
High-Temperature Fuel cells + Gas turbines
-80% of the electrical power comes from the fuel cells
-20% from the gas turbine, which uses the heat evolved by the operating fuel cells.

-In a test, a 250kW Hybrid power plant operated for more than 6000 hours gave minimal Nitrogen Oxide emissions (less than 0.25 ppm) since the turbine was operated with heat from the fuel cells.
These results are now used as basis for building hybrid power plants of Megawatt size.
With improving the turbines
the Efficiency will be:-
Near term: 62%
Medium term: 67
Long term : 74%

With improving the fuel cells themselves
the Efficiency will be:-
Near term: 50%
Medium term: 57%

Small Stationary Power Plants
small power plants are most widely for supplying a combination of (electrical power) and (heat) for communities, especially for remote-areas and as back-up generators for customers who can't tolerate power interruptions.
Applications on
F
uel
C
ells
-fuel cells as a power source for automotive transport applications has been widely used because of the high rates of air pollution that mostly come from the cars which rely on internal combustion engines.
-Types of cars:
1- ICE cars
2- Storage battery cars
3- Hybrid cars
Problems of the use fuel cells:
1- Cost.
2- The production, storage and transport for the Hydrogen used in the fuel cells.
1-
TRANSPORT

2-
PORTABLES
Examples Of Fuel Cell Transport Applications In Real Life:
-a Program called "Clean Urban Transport For Europe":
2000-2006
This program began by involving (27) fuell-cell powered buses in (9) European cities.
It achieved and led to introducing this type of buses to other cities around the world.
-In Spacecrafts:
1-
The Gemini spacecraft in 1960s: 1kW PEMFC plants.
2-
The Apollo Spacecraft in 1970s: Three 1.5kW AFC plants.
3-
The Orbiter Space Shuttles in the present time: Three 12kW AFC plants.
Portables
Electrochemical Power Sources are usually used for Portable devices, especially Galvanic Cells(Batteries).
Rechargeable batteries were developed like Nickel-Cadmium ,Nickel-Hydride and Lithium-ion batteries.
The main problem of the usual rechargeable batteries is that even the most perfect rechargeable batteries hardly meet the desirable targets of
Operating time between recharges.

SOLID-OXIDE FUEL CELLS
Fuel cells of this class are built with solid electrolytes that have unipolar
O2− ion conduction. Best known among these electrolytes is yttria-stabilized zirconia (YSZ), that is, zirconium dioxide doped with the oxide of trivalent yttrium: ZrO₂+10%Y₂O₃ or (ZrO₂)ₒ‚₉₂(Y₂O₃)ₒ‚ₒ₈ . The conductivity of YSZ-type electrolytes becomes acceptable (with values of about 0.15 S/cm) only at temperatures above 900C. For this reason the working temperature of fuel cells having such an electrolyte is between 900 and 1000C.

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