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8/9/2019 Unit 8-Hydrogen and Fuel Cells
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Introduction to AlternativeIntroduction to AlternativeEnergiesEnergies
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After completing this unit you will Understand what hydrogen is and how it
is used as an energy carrier Be able to explain various methods to
Be able to explain the concept of a fuelcell and different types of fuel cells
Have knowledge of different applicationsfor fuel cells
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What is Hydrogen
and how is it used as an energy
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What is Hydrogen? Taken from, Hydrogen Now!
http://www.hydrogennow.org/Facts/whatishydrogen.htm 4
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Its Simple! Hydrogen is the simplest,
lightest element in theuniverse
It is made up of one proton
an one e ectron Because of its simplicity, it is
believed by some thathydrogen is the root of allelements
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Its Light! When hydrogen escapes into
the atmosphere, it is so lightthat it scatters immediatelyupward in the air
It s 14 times ig ter t an air This means that a hydrogen
spill wont pool on theground, pollute groundwater,or soak into clothingitremoves itself!
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Its Everywhere! Hydrogen is the most
abundant element inthe universe, making upmore that 90% of all
On Earth, it is the thirdmost abundant element
in the Earths surface,found in water and allorganic matter
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Whats Its Nature? In its normal gaseous
state, hydrogen is
colorless, odorless, tasteless,colorless, odorless, tasteless,
which makes it
different from everyother common fuelwe use
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What Happens When Hydrogen Burns? Hydrogen burns readily with oxygen, releasing
considerable energy as heat and producingonly water as exhaust
When it burns in air, much fewer pollutants
are orme t an w en norma y rocar onfuels such as gasoline and diesel are burned Because no carbon is involved, using hydrogen
fuel eliminates carbon monoxide, carbondioxide, and does not contribute to globalwarming
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Hydrogen Hydrogen has the highest energy content of
any common fuel by weight (about three times more than gasoline)
But it has the lowest energy content by volume
(about four times less than gasoline)
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Interest in hydrogen hasgrown rapidly over the last50 years, partially due to its
potential as a fuel
Hydrogen is not theenergy itself but an
energy carrier, anavenue for potential energy
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An Energy Carrier A substance or system used to move
energy from one place to another The most common energy carrier today
Electricity carries the energy from coal,oil, gas, and other energy sources to our
industries and homes for use withequipment, appliances, etc.
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Similar to electricity, hydrogen is anenergy carrier
Different from electricity though,hydrogen can be easily stored andtransported
Energy can e store an transporte inhydrogen to be used when and whereneeded
Hydrogen can be used in places where itmay be difficult to get electricity to, suchas a moving automobile
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How can hydrogenbe produced and how is it stored
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Chemical Production of Hydrogen Historically, hydrogen was produced with
methods that involved passing steam over redhot iron filings
steam releasing the hydrogen
Later, hydrogen was produced by reacting iron
with sulfuric acid
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Today, modern production includesmethods such as reactingaluminum chips with caustic acid which is used for meteorological balloons
uses including the food industry,the production of ammonia, small
amounts used in fuel cells to power automobiles, and utilities
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The majority of the hydrogen used today is produced from fossil fuels
The hydrocarbons and alcohols can producehydrogen when submitted to partial oxidation,steam reforming, and thermal decomposition
T ese processes yie syngas , w ic is acombination of hydrogen and carbonmonoxide
There are many processes for hydrogenproduction including chemical, electrolytic,thermolytic, photolytic, and biological
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Electrolytic Hydrogen This process used in the early 1900s, but not
very economical at the time and replaced bythe less expensive fossil fuel plants
Today, with the fossil fuel cost increasing, this
as ecome a via e option Produces very pure, 99.999%, hydrogen and
popular in food and pharmaceutical industries The process shows potential for hydrogen gas
stations for refueling of fuel cells
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Thermolytic Hydrogen At high temperatures a small percentage of
water molecules will separate into hydrogenand oxygen
There are two different methods for the
issociation o water Direct dissociation uses very high temperatures,
over 2000 K to dissociate less than 1% of water,
and over 3000
K to get over 10 % Chemical dissociation does not require as high of
temperatures, 600 C to 850 C , using various
chemicals to aide in the reaction 21
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Photolytic Hydrogen Hydrogen can be produced using solar
light energy, with each step of the reactiontaking a specific amount of energy1. Hydrogen is first separated leaving one
hydrogen
2. Next the remaining hydrogen is separated from the oxygen
3. And in the final step, two oxygen combineand two hydrogen combine
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Photobiologic Hydrogen Production A relative new process being studied When exposed to light, plant species
produce oxygen, and in the dark theyconsume oxygen
In the dark, if the plant has waterand consumes oxygen, hydrogen willbe released
The amount of hydrogen released isminimal relative to the mass of biological material needed
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Hydrogen Production Plants Typically start with a fossil
fuel such as natural gas Large plants, such as those
production of ammonia,are present today
For automobiles, where there is great interestin fuel cells, a compact version of thishydrogen production plant is needed
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Hydrogen Storage There is great potential for hydrogen as a
future energy source It is capable of very high efficiencies, easy to
, The gas is easy to transform into usable
energy and relatively easy to acquire, but the
difficulty lies in the distribution and storageof the gas
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Distribution may not be too difficultas it can be moved similar to natural gas,
distributed through the existing pipelines toresidential and industrial sites
Although the bulk distribution of hydrogenwould not be a major hurdle, the problem liesin the motor vehicles
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Fuel cells are a potential power sourcefor the automobile or any other machinethat has a gasoline engine or similar
power source Getting hydrogen to the fuel cell on a
-difficulty lies
Hydrogen used by a moving vehicle must
either be created by the vehicle itself orsomehow conveniently stored on thevehicle, like gas in a gas tank
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Hydrogen can be stored in two different ways:1. As the gas alone in some sort of container
2. Extracted from a substance as needed for use Storing the hydrogen itself can be done
different ways: as a compressed gas ,re r gera e qu , or a com na on o o
Storage of hydrogen to be extracted is doneseveral different ways including absorption of
the gas on a given substrate or hydrogen richcompounds
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Cryogenic Hydrogen Although the concept of liquid
hydrogen was first developed in1898, it wasnt until just recentlythat the concept was looked at for
Recently looked at by NASA forstoring hydrogen as a fuel for space
craft, with largest storage unit of this type at Cape Canaveral holding240,000 kg of liquid hydrogen
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Storage by Absorption Hydrogen molecules can be readily absorbed
by carbon, and are held in place by weak Vander Waals forces which take little energy toseparate when using as a fuel source
Many i erent systems ave een trie orthis technology The drawback at this time for these systems is
that they require high pressure and lowtemperatures
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Hydrogen Storage-Carriers One way to store hydrogen is with carriers,
material that is synthesized rich in hydrogen When hydrogen is needed, the material is
chemically reformed
This process also is of great interest to the fuelcell vehicles with few difficulties to overcomeas a viable solution
The efficiencies of this system are relativelylow, for example, methanol at only 55%
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Metal hydrides A number of elements that can be used as
metal hydrides include magnesium, iron,titanium, zirconium, with others
Hydrides are formed when hydrogen is
com ine wit t ese e ements an arereferred to as binary This exchange of hydrogen gas with the
elements is referred to as absorption whenthe hydrogen is taken in and desorption whenthe hydrogen is released
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Compared to gasoline (4700MJ per 100 kg) a hydride canhave 515 MJ per 100 kg
Accounting for the higher efficiency of hydrogen, it takesabout 3 times the wei ht o a
hydrate to produce an equal amount of energy compared togasoline
Also promising for hydrides is the fact thatthey need less time to regenerate compared to batteries
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Hydride Heat Pumps Since a hydride absorbs heat when it releases
hydrogen, it is possible to use them as a heatpump
In actuality, the containers would be fixed and
t ere wou e a mec anism to move t efluid from inside to out. This system couldalso be used as a refrigerator
Storage is a key factor in the innovation of hydrogen and the use of fuel cells
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How does a fuel cell work and what are some different
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From reactions to energy A mechanical heat engine uses a fuel such as
gasoline, oil, or wood which is burned creatinga chemical reaction
various mechanisms is transferred to someusable energy such as electricity
The overall process is limited and very inefficient
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Converting electricity directly from thechemical reaction is much more efficientEspecially since the chemical bond of most
molecules is electric in nature Devices that convert chemical energy directly
electrochemical cellselectrochemical cells
Because they convert chemical energy directlyinto electricity, they are much more efficient
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Electrochemical cells can be batteries used intoys, automobile batteries, and fuel cells The terms cell and battery are basically
the same with Cell typically referring to a single unit
And battery referring to a series of units Terminology is not consistent though as in the
example of a 9 volt battery which is a singlecell or a fuel cell which is typically a series of cells or a battery
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There are two categories of batteries or cells Expendable are batteries that we get at the
store, use for toys or other devises, thendispose when they are dead
Non-expendable are either rechargeable orre ue a e
Rechargeable devises would be like our car battery, or cell phone batteries
Refuelable devices would be the fuel cells , devicesthat have a consumable fuel, typically a liquid,that needs replenished
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Electrochemical (Fuel) Cells Consists of a source and a sink of electrons The reaction that takes place in an
electrochemical cell is made up of two half
The two regions are separated by anelectrolyte that allows the conduction of ions
but not electrons
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The source region (anode) contains asubstance such as hydrogen that releaseselectrons; the release of electrons is referred
to as oxidation The electrons flow from the source region to
that gains electrons; the gaining of electrons isreferred to as reduction
A current capable of doing work is thengenerated in the opposite direction of theelectron flow, from the cathode to the anode
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If conductors (electrodes) are present on eachside and are connected, the electrons will flowfrom one side to the other
The external circuit is only a path though, anddoes not force the electrons to flow
T e circuit cou e t oug t o as a pipe
The pipe would be a path but the water would have to be forced to flow through the pipe by some means
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There are several kinds of fuel cells eachoperating a bit differently
In general, a hydrogen fuel cell operates Hydrogen atoms enter a fuel cell at the anode
electrons The hydrogen atoms are now ionized, and
carry a positive electrical charge The negatively charged electrons provide the
current through wires to do work
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Some of the more common fuel cells
Solid Oxide
Phosphoric Acid and P.E.M.
Alkali
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What are somedifferent applications for
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Fuel Cell Applications Fuel cells are in the innovation growth stage, a
time with new and radical developments With these developments, new applications
The two main currentapplications are
stationary power plants and theautomobile
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Power plants Fuel cells are very attractive bringing
advantages such as very little noise and pollutants
Other advantages
mass and volumecompared tooutput of thesystems and thehigh efficiencies
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Automobiles Advantages are
similar for the
automobile, but thedisadvantage is the
the fuel cells Just comparing the power source, fuel cells
have the advantage with higher efficiencies,less weight, less size, less noise, and fewer pollutants
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The disadvantage for fuel cellscomes from the high cost of production
The current gasoline engine used forthe automobile is mass produced
Fuel cells do not have any of thiscurrently and the cost to develop
this industry makes the entry costfor fuel cells very high
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Work Cited Da Rosa, A. V. (2005). Fundamentals of Renewable Energy Processes. Burlington, MA,
USA: Elsevier Inc.
http://www.fctec.com/fctec_basics.asp
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