See polarization below.
The point in time when a reaction occurs. You know how it is when the school bully picks
on you. It takes a while, but after a bit, you blow up. That's the point of "activation"
for you. The conditions are right for activation, but you don't activate until that
particular point in time. So it is with chemical reactions. The time it takes between
when conditions are right for the reaction to occur and the time the reaction actually
occurs, is activation time.
Adobe is a computer imaging company that has chosen to give away its PDF (portable
document format) reader. Thus, most of the internet community puts out documents in
PDF format. The reader automatically loads into the browser when the browser tries to
load a file with the extension .pdf if adobe acrobat reader is installed on the computer.
for a free download of the Adobe Acrobat Reader. If your browser does not load acrobat
when you click on a pdf file, try loading acrobat first. Generally it can be recognized
by the browser if it is already loaded and running.
Caveat: it is not the purpose of Thinkquest to recommend products or to sell products
on the internet. The purpose of this link is a convenience for our readers.
Alkaline fuel cells
This cell was used in the Apollo and Shuttle Orbiter craft. It uses potassium hydorxide
as an electrolyte. It needs fuel free of carbon dioxide (the hydrogen and oxygen must
be pure). The problem of slow reaction due to low operating temperature is cured through
pressure, porous electrodes, and platinum catalyst. Hydroxide ions (OH-) flow from
cathode to anode. The reactions are like so:
These are negative ions, such as OH- (hydroxide) ions in the alkaline fuel cells.
An electrode in a fuel cell. The electrons flow from the anode to the cathode. In
the alkaline fuel cell, the hydroxide ions (OH-) flow from the cathode to the anode.
It is where oxidation occurs.
This is a popular term used in climate change discussions. It describes a link between
changes in the environment, climate, or eco-systems due to human action. In other
words, it is when humans are responsible for these changes, i.e., greehnouse gas emissions.
BAU - Business as usual
Emission levels in the absence of any new policies or measures to limit the growth
of greenhouse gas emissions.
Biomass is organic waste material.
Most often this term is used to refer to the cellulose coming from paper and wood
products. Certain bacteria feed on this material and produce hydrogen and hydrocarbons
(such as methane or natural gas).
One of the problems in fuel cells is voltage drop on the electrodes as fuel is used
on their surface. To provide a more equal distribution of fuel over the electrodes,
bipolar plates are used, which consist of groves, where hydrogen is blown through the
groves north to south with oxygen being blown through the groves east to west. This gives
greater coverage of the fuel distribution on the electrode surfaces.
Anything used in the fuel cell to increase gas pressure. Blowers are also used to
remove heat from the fuel cell. The blower pumps hydrogen to the anode, oxygen to the
cathode, and cooling gas - all through different groves in the
British thermal unit. Amount of heat to raise one pound of water 1°F.
To separate or break off a piece of an ice mass so that it becomes
The global exchange of carbon between atmosphere, oceans, vegetation, soils, and earthly
The fixing of carbon dioxide by ontake in trees and plants, where carbon dioxide is
A reservoir that stores carbon, such as trees or the ocean.
Tax on fossil fuels proportional to the carbon content of each fuel.
Any chemical substance that speeds up the reaction. It is not chemically changed, itself,
in the reaction. Its effect is to enable the reaction to occur with less heat. It
effectively lowers the activation
The cathode is always the electrode into which electrons flow.
These are positively charged particles. Hydrogen protons fit this definition in fuel
CCAP - Climate Change Action Plan
President Clinton's 50 voluntary federal programs designed to reduct
greenhouse gases to 1990 levels by 2000. It complied with the terms
of the Framework Convention on Climate Change.
These are fuel cell systems that operate with high voltage and current and at high
Circuit - An electrical circuit is a path over a conductive surface where electrons move
from a power supply from its anode to the cathode. Circuits are rated like so:
High voltage - more than 600 volts
Low voltage - 31 to 600 volts
Extra low voltage - up to 30 volts
COP - Conference of the Parties
A meeting of the nations that ratified the
FCCC (Framework Convention on CLimate Change).
Electrical current is a flow of electrons from the anode to the cathode of an electrical
Change of forests to non-forest through either harvesting or burning. The net result
is an increase in the greenhouse gas, carbon dioxide.
You know how you are really fresh in the morning? As the day wears on, you wear out, to the
point where you need to rest again in the night. You know how those batteries you bought
for the boombox wear down over time? So it is for the fuel cell. A new fuel cell will
be 25% over its rated voltage. Over time it wears down to below its rated voltage, at
which time it has to be replaced. This is called degradation. The time it takes (time used)
is called the rate of degradation. It is measured in volts per time unit. In other words,
my fuel cell for my boombox has a degradation rate of .5 volts per 4,000 hours of use.
Direct internal reforming
See reforming below. In a process like
this, the temperature is so high, that the hydrocarbon fuel is broken down as it enters
the fuel cell chamber. All that's necessary is to feed the hydrogen to the anode. Hydrocarbons
used are gasoline, methanol, methane, etc.
This is a measure of the amount of energy applied to produce work (work in the context of a
fuel cell is moving electrons through the anode to the cathode) compared with the total
energy applied. The difference is called
entropy, or wasted energy (usually in the form of heat), like so:
Efficiency = Energy doing work ÷ Total energy used
Sadi Carnot, the father of thermodynamics, came up with this concept studying steam
engines in Napoleonic France.
Either of the two conductors of an electrical power source. The anode is the positive
terminal and the cathode is the negative terminal. Electrons flow from the anode to
A substance that allows the flow of ions,
which enable it to conduct a limited amount of
electrical current. It can be liquid, gas or solid - depending on the type of
fuel cell (see our discussion of fuel cells in the hydrogen section).
This means girl child in Spanish. It causes warm weather to change to cold weather and
back again to warm. It draws thunderstorms. La Niña is caused by winds blowing westward
from the equator to the eastern Pacific Ocean. Upwelling occurs, which moves cold water
from the bottom. So La Niña cools down the air.
This means the boy in Spanish. It was so named for the Christ child, because these
types of storms appeared first during the Christmas season. The effect is a shifting
of the direction of winds and an increase in temperature. The areas affected are the
Pacific. The United States, North America, and Central America are interested in
study of El Niño. This is caused by warming the Pacific Ocean at the equator. It
makes the northern United States hot and dry, and the southern United States wet and stormy.
A reaction that needs a heat supply. The reaction takes or uses heat.
In doing work, energy is used. Entropy is the energy in that process that cannot be
used to perform that mechanical work. Entropy arises from friction in most machinery,
for instance. The energy that goes into entropy is wasted, as it were. In cases where
the energy that is not converted to work can be captured and run back through the system
it be a part of the process of doing work, is called
In external reforming, hydrogen is
made from hydrocarbon source gases (propane, methanol, natural gas, gasoline, etc.)
before it enters the fuel cell, as opposed to
direct reforming, where the conversion happens inside the fuel cell.
FCCC - Framework Convention on Climate Chante
The United Nations Conference on Environmental Development (UNCED) held a convention in
Rio June 1992 for the signing of a treaty to decrease
greenhouse gas emissions. 155 countryies have ratified this treaty.
Connecting one system to another. The result is positive (where one enhances the effect
of the other) or mitigating (where they quiet each other's effect).
Geologic deposits of carbon stores in reduced organic form and of biological origin.
Examples are coal, natural gas, oil shales, and tar sands. When these are burned
for energy needs, they contribute greenhouse gas to the atmosphere.
That which removes water from an alkaline fuel cell or carbon dioxide from an alkaline
fuel cell. Filters remove either gases or liquids that are not needed or that are at
too high a concentration from the fuel cell. Water has to be removed from liquid fuel
cells. Water is produced in the fuel cell as a byproduct.
An environmental footprint is evidence that human beings have impacted the ecological
systems, climate change, or environment. It usually has negative connotations.
Electrical power source that oxidizes a fuel and produces electricity without moving parts.
This source is attractive because it facilitates operating a car with the polluting
nitrogen oxides. Fuel cells are identified by their electrolyte and fuel, like so:
The increase of 1%#176;F over the past 140 years in temperature on the earth's surface
atmosphere. Greenhouse gases
cause the earth to warm.
Any gas that absorbs infra-red solar radiation. They include carbon dioxide,
methane, nitrous oxide, halogenated fluorocarbons, hydrofouorocarbons, ozone,
perfluorinated carbons, and water vapor,
This is a compound (see our compound discussion) containing carbon and hydrogen bonded
together. Such compounds are fossil fuels, methane, propane, butane, etc.).
An electrically charged particle of an atom or an atom in whole (see our discussion of the
polymer used in PEM fuel cells in the fuel cell section of the hydrogen section).
Materials that allow ions to pass discrimantly, like hydrogen proton through the
solid electrolyte plastic of a PEM fuel cell are by their logically cute name of "ionomers"
by some scientist in the fuel cell industry.
IPCC - Interbovernmental Panel on Climate Change
Established in 1988 by the United Nations Environment Programme and the World Meteorological
Organization by 60 nations to study and assess climate change.
This is emissions trading on an international scale (well, sort of). It is one of the allowed
alternatives in the Kyoto Protocol where one country can implement projects that
reduce emissions in another country to count towards its own share of emissions
This is a term one sees all over the fuel cell literature. It is more than just another
word for electrode, really. More so, it includes the whole sandwich. These things are getting
smaller and smaller, like computer chips. And the assembly process is very similar to that
of computer chips. The MEA consists of the anode, cathode, and the solid electrolyte
bipolar plates for gas diffusion, and catalystic coatings.
Generally a polymer that is placed between the anode and cathode of a fuel cell. It
serves as an electrolyte. It allows ion exchange between the anode and cathode as fuel
and oxygen comes in through each of these terminals. The membrane block the mixing of
the gases, keeping them separated (fuel to anode and oxygen to cathode in most fuel
DMFC - direct methanol fuel cell
This is a fuel cell where methanol (CH3OH) is oxidized directly at the anode, with no
reformation of hydrogen in the process,
Emission from vehicles which combines with ozone to produce smog. It contains one
nitrogen molecule and one or more oxygen molecules. It is classed a pollutant.
N2O. This is a powerful greenhouse gas. Fossil fuel and boimass combustion
produce nitrous oxide.
OCV - open circuit voltage
This is the voltage of a fuel cell circuit when it has no
load is attached.
This is the loss of power in the fuel cell. We measure it by voltage drop. It occurs
by resistance in a conductor. In fuel cells, resistance to flow of electrons or
other ions, such as hydroxide in the alkaline fuel cell, occur in both the electrode
materials and in the electrolyte.
O3 contains three oxygen atoms bound together. It protects us from from
dangerous ultraviolet radiation. Ozone is found to be 90% of the
stratosphere. It forms smog in the
PAFC = phosphoric acid fuel cell
These systems operate at high temperature and were the first commercially used fuel cells.
They operate at 428°F and use reforming to get hydrogen fuel. Reforming uses CH
4 (methane) and produces carbon
dioxide as a byproduct. This is done externally. The fuel cell operates similarly to the
PEM fuel cell. The fuel cell uses
phosphoric acid (H3PO4). The reaction is like so:
joint implementation schemes (this is where one country pays for programs to contract
emissions in another country for "emissions credits" for the emissions saved.
solutions to contract emissions sources
You know how after a while you hear a rumbling in your car from the ball bearings going out
on a pump that recycles exhaust back to convert the CO to CO2. The same thing
applies in the reformation process
in fuel cell technology. On first pass, one gets a lot of carbon monoxide, rather than
carbon dioxide. On first pass, rather than getting water, one gets hydrogen. One second
pass, the oxidation produces water and carbon dioxide. Partial oxidation is superior
to passing steam over carbon (coal) because it releases heat rather than using heat from
an outside source.
PEM or Proton Exchange Membrane
Proton exchange membrane fuel cell, named for the fact that a hydrogen proton (H+) can
pass through the membrane in an solid polymer fuel cell. Hydrogen gas comes in through
a porous anode. The electron flows through the anode wire to the cathode. The proton
passes through the anode membrane, combines with oxygen on the cathode. So water is
only produced on the cathode electrode in this type of fuel cell. PEMs are also known as
acid fuel cells.
The process of converting polyethylene to polytetrafluoroethylene by substituting
fluorine for hydrogen.
A process where plants produce a reservoir of carbon dioxide by fixing it in sugars.
The plant gives off oxygen and water in the process.
Polarization (or activation polarization)
If you apply heat to a piece of paper, at a point in time it ignites. It might remain
in a state of non-combustion for a while, but when the conditions are right (heat high enough
and oxygen available), after it passes an "activation barrier," it catches on fire. So
it is with the fuel cell. When the
kinetics of the reaction on
the electrodes are slow, the charges (pre-reaction) have built up. As the electrons move
and the protons (if an acid cell) bond with oxygen and accept the electron flowing to
the cathode from the anode, the reaction "activates" again. So polarization puts a
bottleneck in the reaction, slowing it down, which we call "voltage drop."
PTFE = polytetraflouroethylene
This is polymer that has been perfluorinated or that has had the hydrogen molecules
replaced with fluorine molecules. We call it Teflon. It allows hydrogen protons to
pass through it and it repels water. It is perfect for an electrolyte in a fuel cell.
It goes between the anode and cathode.
QUELROs - Quantitative emission limitation and reduction objectives
This was coined by IPCC people.
This works with the premise that wealth comes from using fossil fuels. This wealth and
use is equated to a big "cake." There are two considerations here:
how big should the cake be
how to fairly divide up the cake among the nations
The second consideration gets into the following three things:
equiy - the cake is divided on a per capital (per head, per population) basis
differentiation - the cake is divided with per capital going to some nations than
others. The disparity brings a cost, where the differentiation is paid out from the
higher per capita consumer to the lesser consumer nation.
This is the use of fossil fuel or
hydrocarbon compounds to produce a fuel cell fuel or to make hydrogen for the
fuel cell fuel. In the one case, steam converts carbon to hydrogen and carbon dioxide.
The hydrogen is used as a fuel.
See direct reforming above.
See external reforming above.
Reversible fuel cell
The concept of reversibility has two meanings in the fuel cell world. First, in
the thermodynamics of fuel cells it is the ability to capture lost energy in a reaction
and recycle it to produce work. In the second sense, it means that the fuel cell can
be recharged. This is when hydrides are used to release hydrogen when exposed to
water, as in power balls (see our sources of hydrogen discussion). The reaction to
produce the hydrogen is like so:
NaH + H2) -> NaOH + H2
The waste NaOH solution is exposed to heat, hydrogen, and pressure, like so:
NaOH + H2 + heat -> NaH + H2O
Of course the water float off to the clouds through evaporation, so actually you get
a drying effect.
Process that removes carbon dioxide from the atmosphere and retain it for some time in
a carbon sink (i.e., trees).
The voltage of a single fuel cell is 1.2 volts in
an open circuit and about .7 volts in a closed circuit with a
load. To increase the voltage, just like is done to
increase battery voltage, one hooks the circuits up in series. With fuel cells, this is
a bit different, because the idea is to increase the surface where the reactants are.
So rather than hook up a single point on the electrode, there are several "interconnecting"
The voltage of a fuel cell is around .7 volts when the circuit is closed. To increase
the voltage, the cells are connected in a series, or a stack.
The layer of atmosphere above the
troposphere. It runs from 11 mile to 31 miels up.
The lowest layer of the atmosphere, six to nine miles up.
Zero emission vehicle
The state of California USA passed a law in 1990 that required that 10% of the vehicles
in the state would have to have zero emissions (of nitrogen oxides, lead, and other
pollutants) by 2003. This has generated a hubbub and has really helped focus the rest
of the world on the whole issue of alternatives to fossil fuels. So the exciting time
to see in the future will occur around 2003 or 2004.