Fuel Cells technology

8/3/2019 Fuel Cells technology

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Hatim Ksissou

by: Hatim Ksissou

SEM3511: Introduction to Physics for En

Fuel Cell Technology


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2 Fuel Cell Technology | by: Hatim Ksissou

Table of Contents

i. What is a fuel cell? ...................................................................................................................... 3

a. Definition: ............................................................................................................................... 3

ii. How do they work? ..................................................................................................................... 3

a. The theoretical process ............................................................................................................ 3

iii. Where does hydrogen comes from? ............................................................................................ 4

iv. Why cant we buy a fuel cell?..................................................................................................... 5

a. Limitations .............................................................................................................................. 5

b. What's holding back use of fuel cells? .................................................................................... 6

c. Can I use a fuel cell to power my home? ................................................................................ 6

v. Types of fuel cells. ...................................................................................................................... 7

a. Alkali Fuel Cells...................................................................................................................... 7

b. Molten Carbonate fuel cells .................................................................................................... 7

c. Phosphoric Acid fuel cells....................................................................................................... 7

d. Proton Exchange Membrane fuel cells.................................................................................... 8e. Solid Oxide fuel cells .............................................................................................................. 8

vi. Applications ................................................................................................................................ 8

a. Telecommunications............................................................................................................ 9

b. Transportation ......................................................................................................................... 9

vii. Advantages: ........................................................................................................................... 10

viii. Disadvantages........................................................................................................................ 12

ix. Case Problem ............................................................................................................................ 13

Bibliography ..................................................................................................................................... 14


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i. What is a fuel cell?a. Definition:

A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has twoelectrodes, one positive and one negative, called, respectively, the anode and cathode. The

reactions that produce electricity take place at the electrodes. 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.

Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that

they generate electricity with very little pollutionmuch of the hydrogen and oxygen used in

generating electricity ultimately combine to form a harmless byproduct, namely water.

One detail of terminology: a single fuel cell generates a tiny amount of direct current (DC)

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

principles are the same.

ii. How do they work?a. The theoretical process

In principle, a fuel cell operates like a battery. Unlike a battery, a fuel cell does not run down or

require recharging. It will produce energy in the form of electricity and heat as long as fuel is

supplied.


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The fuel cell works by injecting molecular hydrogen (H2) molecules into the anode. The

hydrogen molecules react with the catalyst. The catalyst is usually a thin coat of powdered

platinum on carbon paper. This breaks up the hydrogen into a proton and an electron. The

proton goes across the electrolyte, while the electron is fed through the circuit and goes to work,

whether it be powering your oven or providing horsepower to your new ustang.

Upon finishing their job, the electrons return to the cell through the cathode. There, the catalyst

assists the oxygen molecules, the hydrogen protons and the hydrogen electrons in making water.

The chemical reactions are the following:

Anode:

2H2 => 4H+ + 4e-

Cathode:O2 + 4H

++ 4e

-=> 2H2O

The whole reaction ends up looking like this:

2H2 + O2 => 2H2O

This reaction only creates about 0.7 volts. Because of this, there are several cells built into a

stack. This multiplies the voltage up to useable levels.

iii. Where does hydrogen comes from?A fuel cell system which includes a "fuel reformer" can utilize the hydrogen from any

hydrocarbon fuel - from natural gas to methanol, and even gasoline. Since the fuel cell relies

on chemistry and not combustion, emissions from this type of a system would still be much

smaller than emissions from the cleanest fuel combustion processes.

Reformers - Fuel cells generally run on hydrogen, but any hydrogen-rich material can serve

as a possible fuel source. This includes fossil fuelsmethanol, ethanol, natural gas, petroleum

distillates, liquid propane and gasified coal. The hydrogen is produced from these materials

by a process known as reforming. This is extremely useful where stored hydrogen is not

available but must be used for power, for example, on a fuel cell powered vehicle. One

method is endothermic steam reforming. This type of reforming combines the fuels with

steam by vaporizing them together at high temperatures. Hydrogen is then separated out using


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membranes. One drawback of steam reforming is that is an endothermic process meaning

energy is consumed. Another type of reformer is the partial oxidation (POX) reformer. CO2 is

emitted in the reforming process, which makes it not emission-free, but the emissions of

NOX, SOX, Particulates, and other smog producing agents are probably more distasteful than

the CO2. And fuel cells cut them to zero.

Enzymes - Another method to generate hydrogen is with bacteria and algae. The

cyanobacteria, an abundant single-celled organism, produces hydrogen through its normal

metabolic function,. Cyanobacteria can grow in the air or water, and contain enzymes that

absorb sunlight for energy and split the molecules of water, thus producing hydrogen. Since

cyanobacteria take water and synthesize it to hydrogen, the waste emitted is more water,

which becomes food for the next metabolism.

Solar- and Wind- powered generation - By harnessing the renewable energy of the sun and

wind, researchers are able to generate hydrogen by using power from photovoltaics (PVs),

solar cells, or wind turbines to electrolyze water into hydrogen and oxygen. In this manner,

hydrogen becomes an energy carrierable to transport the power from the generation site to

another location for use in a fuel cell. This would be a truly zero-emissions way of producing

hydrogen for a fuel cell.

iv. Why cant we buy a fuel cell?a. Limitations

The basic workings of a fuel cell may not be difficult to illustrate. But building inexpensive,

efficient, reliable fuel cells is a far more complicated business.

Scientists and inventors have designed many different types and sizes of fuel cells in the search for

greater efficiency, and the technical details of each kind vary. Many of the choices facing fuel cell

developers are constrained by the choice of electrolyte. The design of electrodes, for example, and

the materials used to make them depend on the electrolyte. Today, the main electrolyte types are

alkali, molten carbonate, phosphoric acid, proton exchange membrane (PEM) and solid oxide. The

first three are liquid electrolytes; the last two are solids.


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The type of fuel also depends on the electrolyte. Some cells need pure hydrogen, and therefore

demand extra equipment such as a reformer to purify the fuel. Other cells can tolerate some

impurities, but might need higher temperatures to run efficiently. Liquid electrolytes circulate in

some cells, which require pumps. The type of electrolyte also dictates a cells operating

temperaturemolten carbonate cells run hot, just as the name implies.

Each type of fuel cell has advantages and drawbacks compared to the others, and none is yet cheap

and efficient enough to widely replace traditional ways of generating power, such coal-fired,

hydroelectric, or even nuclear power plants.

b. What's holding back use of fuel cells?Many technical and engineering challenges remain; scientists and developers are hard at work

on them. The biggest problem is that fuel cells are still too expensive. One key reason is that

not enough are being made to allow economies of scale. When the Model T Ford was

introduced, it, too, was very expensive. Eventually, mass production made the Model T

affordable.

c. Can I use a fuel cell to power my home?Fuel cells are ideal for power generation, either connected to the electric grid to provide

supplemental power and backup assurance for critical areas, or installed as a grid-independentgenerator for on-site service in areas that are inaccessible by power lines. Since fuel cells

operate silently, they reduce noise pollution as well as air pollution and the waste heat from a

fuel cell can be used to provide hot water or space heating.

There are three main components in a residential fuel cell system - the hydrogen fuel

reformer, the fuel cell stack and the power conditioner. Many of the prototypes being tested

and demonstrated extract hydrogen from propane or natural gas. The fuel cell stack converts

the hydrogen and oxygen from the air into electricity, water vapor and heat. The powerconditioner then converts the electric DC current from the stack into AC current that many

household appliances operate on. The initial price per unit in low volume production will be

approximately $1,500 per kW. Once high volume production begins, the price is expected to

drop to $1,000 per kW, with the ultimate goal of getting costs below $500 per kW. Fuel cell

developers are racing to reach these cost targets.


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Many companies are developing and testing fuel cells for stationary and residential

applications, working together with utilities and distributors to bring them to market. Even

automakers such as GM, Honda and Toyota are branching beyond vehicles and spending

money on research and development for stationary applications.

v. Types of fuel cells.The following list describes the five main types of fuel cells.

a. Alkali Fuel CellsTheyoperate on compressed hydrogen and oxygen. They generally use a solution of potassium

hydroxide (chemically, KOH) in water as their electrolyte. Efficiency is about 70 percent, and

operating temperature is 150 to 200 degrees C, (about 300 to 400 degrees F). Cell output ranges

from 300 watts (W) to 5 kilowatts (kW). Alkali cells were used in Apollo spacecraft to provide

both electricity and drinking water. They require pure hydrogen fuel, however, and their platinum

electrode catalysts are expensive. And like any container filled with liquid, they can leak.

b. Molten Carbonate fuel cellsThey use high-temperature compounds of salt (like sodium or magnesium) carbonates

(chemically, CO3) as the electrolyte. Efficiency ranges from 60 to 80 percent, and operating

temperature is about 650 degrees C (1,200 degrees F). Units with output up to 2 megawatts (MW)

have been constructed, and designs exist for units up to 100 MW. The high temperature limits

damage from carbon monoxide "poisoning" of the cell and waste heat can be recycled to make

additional electricity. Their nickel electrode-catalysts are inexpensive compared to the platinum

used in other cells. But the high temperature also limits the materials and safe uses of MCFCs

they would probably be too hot for home use. Also, carbonate ions from the electrolyte are used up

in the reactions, making it necessary to inject carbon dioxide to compensate.

c. Phosphoric Acid fuel cells


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They use phosphoric acid as the electrolyte. Efficiency ranges from 40 to 80 percent, and

operating temperature is between 150 to 200 degrees C (about 300 to 400 degrees F). Existing

phosphoric acid cells have outputs up to 200 kW, and 11 MW units have been tested. PAFCs

tolerate a carbon monoxide concentration of about 1.5 percent, which broadens the choice of fuels

they can use. If gasoline is used, the sulfur must be removed. Platinum electrode-catalysts are

needed, and internal parts must be able to withstand the corrosive acid.

d. Proton Exchange Membrane fuel cellsThey work with a polymer electrolyte in the form of a thin, permeable sheet. Efficiency is

about 40 to 50 percent, and operating temperature is about 80 degrees C (about 175 degrees F).

Cell outputs generally range from 50 to 250 kW. The solid, flexible electrolyte will not leak or

crack, and these cells operate at a low enough temperature to make them suitable for homes andcars. But their fuels must be purified, and a platinum catalyst is used on both sides of the

membrane, raising costs.

e. Solid Oxide fuel cellsThey use a hard, ceramic compound of metal (like calcium or zirconium) oxides (chemically,

O2) as electrolyte. Efficiency is about 60 percent, and operating temperatures are about 1,000

degrees C (about 1,800 degrees F). Cells output is up to 100 kW. At such high temperatures a

reformer is not required to extract hydrogen from the fuel, and waste heat can be recycled to make

additional electricity. However, the high temperature limits applications of SOFC units and they

tend to be rather large. While solid electrolytes cannot leak, they can crack.

vi. ApplicationsMore than 2500 fuel cell systems have been installed all over the world in hospitals,

nursing homes, hotels, office buildings, schools, utility power plants - either connected to the

electric grid to provide supplemental power and backup assurance for critical areas, or

installed as a grid-independent generator for on-site service in areas that are inaccessible by

power lines.


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Fuel cell power generation systems in operation today achieve 40 percent fuel-to-electricity

efficiency utilizing hydrocarbon fuels. Since fuel cells operate silently, they reduce noise

pollution as well as air pollution and when the fuel cell is sited near the point of use, its waste

heat can be captured for beneficial purposes (cogeneration). In large-scale building systems,

these fuel cell cogeneration systems can reduce facility energy service costs by 20% to 40%

over conventional energy service and increase efficiency to 85 percent

a. Telecommunications:With the use of computers, the Internet, and communication networks steadily increasing,

there comes a need for more reliable power than is available on the current electrical grid, and

fuel cells have proven to be up to 99.999% (five nines) reliable. Fuel cells can replace

batteries to provide power for 1kW to 5kW telecom sites without noise or emissions, and are

durable, providing power in sites that are either hard to access or are subject to inclement

weather. Such systems would be used to provide primary or backup power for telecom switch

nodes, cell towers, and other electronic systems that would benefit from on-site, direct DC

power supply.

b. Landfills/Wastewater Treatment Plants/Breweries/Wineries-Fuel cells currently operate at landfills and wastewater treatment plants across the country,

proving themselves as a valid technology for reducing emissions and generating power fromthe methane gas they produce. They are also installed at several breweries and a winery-

Sierra Nevada, Kirin, Asahi and Sapporo and Napa Wine Company. Untreated brewery

effluent can undergo anaerobic digestion, which breaks down organic compounds to generate

methane, a hydrogen rich fuel.

c. TransportationCars - All the major automotive manufacturers have a fuel cell vehicle either in development

or in testing right now, and several have begun leasing and testing in larger quantities.

Commercialization is a little further down the line (some automakers say 2012, others later),

but every demonstration helps bring that date closer.

Buses - Over the last four years, more than 50 fuel cell buses have been demonstrated in

North and South America, Europe, Asia and Australia. Fuel cells are highly efficient, so even


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if the hydrogen is produced from fossil fuels, fuel cell buses can reduce transit agencies CO2

emissions. And emissions are truly zero if the hydrogen is produced from renewable

electricity, which greatly improves local air quality. Because the fuel cell system is so much

quieter than a diesel engine, fuel cell buses significantly reduce noise pollution as well.

Trains - Fuel cells are being developed for mining locomotives since they produce no

emissions. An international consortium is developing the worlds largest fuel cell vehicle, a

109 metric-ton, 1 MW locomotive for military and commercial railway applications.

Planes - Fuel cells are an attractive option for aviation since they produce zero or low

emissions and make barely any noise. The military is especially interested in this application

because of the low noise, low thermal signature and ability to attain high altitude. Companies

like Boeing are heavily involved in developing a fuel cell plane.

Boats - For each liter of fuel consumed, the average outboard motor produces 140 times the

hydrocarbons produced by the average modern car. Fuel cell engines have higher energy

efficiencies than combustion engines, and therefore offer better range and significantly

reduced emissions. 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.

vii. Advantages:The main advantages of fuel cells are:

Efficiency - Fuel cells are generally more efficient than combustion engines as they are not limited

by temperature as is the heat engine. Because they make energy electrochemically, and do not

burn fuel, fuel cells are fundamentally more efficient than combustion systems. When the fuel cell

is sited near the point of use, its waste heat can be captured for beneficial purposes (cogeneration).

In large-scale building systems, these fuel cell cogeneration systems can reduce facility energy

service costs by 20% to 40% compared to conventional energy service.


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Fuel cell power generation systems in operation today achieve 40% to 50% fuel-to-

electricity efficiency utilizing hydrocarbon fuels.

Systems fueled by hydrogen can consistently provide more than 50 percent efficiency.

Even more efficient systems are under development.

In combination with a turbine, electrical efficiencies can exceed 60 percent.

When waste heat is put to use for heating and cooling, fuel utilization can

exceed 85 percent.

Fuel cell passenger vehicles are expected to be up to three times more efficient than

internal combustion engines, which now operate at 10 to 16 percent efficiency.

Simplicity - Fuel cells are essentially simple with few or no moving parts. High reliability may be

attained with operational lifetimes exceeding 40,000 hours (the operational life is formally over

when the rated power of the fuel cell is no longer satisfied) [3-5].

Low emissions - Fuel cells running on direct hydrogen and air produce only water as the

byproduct.

Engine Type Water Vapor/mile Carbon Dioxide/mile

Gasoline Combustion 0.39 lb. 0.85 lb.

Fuel Cell Running on Hydrogen from Gasoline 0.32 lb. 0.70 lb.

Fuel Cell Running on Hydrogen from Methane 0.25 lb. 0.15 lb.

Fuel Cell Running on Renewable Hydrogen 0.25 lb. 0.00 lb.


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Silence - The operation of fuel cell systems are very quiet with only a few moving parts if any.

This is in strong contrast with present combustion engines.

Flexibility - Modular installations can be used to match the load and increase reliability of the

system. Most fuel cells run on hydrogen and will continue to generate power as long as fuel is

supplied. The fuel cell doesn't care where the hydrogen comes from, so a fuel cell system that

includes a "fuel reformer" can generate hydrogen from diverse, domestic resources including fossil

fuels, such as natural gas and coal; alcohol fuels, such as methanol or ethanol; from hydrogen

compounds containing no carbon, such as ammonia or borohydride; or from biomass, methane,

landfill gas or anaerobic digester gas from wastewater treatment plants . Hydrogen can also be

produced from electricity from conventional, nuclear or renewable sources such as solar or wind.

viii. DisadvantagesThe principal disadvantages of fuel cells, however, are the relatively high cost of the fuel cell, and

to a lesser extent the source of fuel. For automotive applications a cost of US$10 to $50 per kW

and an operation life of 4000 hours is required in order to compete with current internal

combustion engine technology. For stationary combined heat and power systems a cost of

US$1000 per kW and an operation life of 40,000 hours is required. The current cost of a fuel cell

system is around US$3000 per kW for large systems with additional costs required for the heat


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exchanger in the combined heat and power systems. The cost of fuel cells will be brought down

with mass manufacture and costs of US$100 per kW have been predicted as the production of fuel

cells expand over the following few years.

ix. Case ProblemWhat type to use for continuous production of 1 MW?

Alkali Type: cannot be used since the cell output range is limited to a maximum of 5KW.

->Molten Carbonate: can have an output up to 2 MW, so it is the one suitable if we want

to produce continues 1MW of electricity. but it requires high temperature input.

The remaining types: cannot be used since their output range is limited and do not reach 1

MW.


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Bibliography

A Basic Overview of Fuel Cell Technology. n.d. 25 November 2011

.

Fuel For the Futur. n.d. 1 December 2011

.

The online Fuel Cell information Ressource. n.d. 25 November 2011 .

J. Larminie, and A. Dicks, Fuel Cell Systems Explained, John Wiley and Sons, November 2000.

Holland, Zhu, & Jamet. Fuel cells technology and applications. Retrieved

from:http://services.eng.uts.edu.au/cempe/subjects_JGZ/eet/AUPEC01_111.pdf
http://services.eng.uts.edu.au/cempe/subjects_JGZ/eet/AUPEC01_111.pdfhttp://services.eng.uts.edu.au/cempe/subjects_JGZ/eet/AUPEC01_111.pdfhttp://services.eng.uts.edu.au/cempe/subjects_JGZ/eet/AUPEC01_111.pdfhttp://services.eng.uts.edu.au/cempe/subjects_JGZ/eet/AUPEC01_111.pdf

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