Hydrogen Fuel Cell
The first person to invent a hydrogen fuel cell was William Grove in 1839. Grove's
fuel cell
was an alkaline type.
Fuel cells are typed by the kind of
electrolyte they use (as will be explained below).
Fuel cells
are of two general types: mobile (portable, as in cars, flashlights, boom boxes,
lap tops, and cell phones) and stationary (fixed, structural - like a power plant).
Many types of fuel cells will be explained in this section.
Fuel cells produce electrical
energy from hydrogen without any moving parts.
Alkaline fuel cells
- potassium hydroxide electrolyte - the first kind - used in
Apollo space vehicles. This is diagrammed immediately below.
Alkaline fuel cells operate at
temperatures between 122°F and 392°F.
Proton exchange membrane
- a solid polymer fuel cell using a
perfuluorosulfonic acid
plastic, which allows hydrogen protons to pass through.
PEMs operate at temperatures
between 122°F and 212¯F.
Phosphoric acid fuel cells
- these were the earliest commercial cells developed because
they worked best in handling the carbon produced in producing the hydrogen from
reforming
carbon sources like fossil fuel or methane gas.
PAFC
CHP systems operate at
around 428°F. They can generate 200,000 watts of electrical power.
Solid oxide fuel cells
- use hot ceramic material for ionic
flow. The high temperature makes
reforming methane easier for producing the hydrogen
needed for the
process. They operate between 932°F and 1,832°F.
SOFCs generate power from
2,000 watts to several megawatts.
Alkaline fuel cell
What follows is an explanation of the
alkaline fuel cell.
The anode
and cathode are made of porous materials.
In such materials, like a sponge, the two gasses
soak into the materials. While the
electrolyte
is not a good conductor, it produces OH- or
hydroxyl ions,
which facilitate the oxidation
reaction and produce electron flow, which generates
an electrical current.
Hydroxyl ions meet with
hydrogen coming in through the porous
anode, to produce water. After the
water formation, the electrons are released and
flow through the anode.
The chemical
equation is as follows:
Today production and research is turning away from the
alkaline fuel cell to the
PEM.
NASA used the alkaline
and gave it fame in the Apollo and space shuttles.
The problem is the reaction:
2KOH + CO2 ® K
2CO3 + H2O
Potassium hydroxide is changed to potassium carbonate and water. So, unlike
PEM, air
with carbon dioxide cannot be used. One must use pure hydrogen. So we need a process
to get rid of the carbon dioxide and the water.
One solution to the water removal is to circulate hydrogen. But then, what if the
gases get mixed (i.e., hydrogen on the
cathode and oxygen migrating to the
anode)?
This generates a short
circuit, because the electrons will not flow through the
anode
to the cathode,
but flow directly to the cathode
through the electrolyte.
The next solution is to make the
electrolyte
solid (to avoid the pumping of the liquid
electrolyte with its related problems).
A variation is to use hydrazine (H2NNH2) or methanol
(CH3OH) as fuels. The reaction for methanol is:
CH3OH + 6OH- ®
5H2O + CO2 + 6e-
The production of nitrous oxide and carbon dioxide is not exactly a total "clean"
environmental optimal situation.
PEM fuel cells
PEMFC
stands for proton exchange
membrane fuel cell. This is because the
electrolyte
is a
solid polymer (like plastic, we'll explain below).
The polymer we're going to eventually make allows hydrogen protons to pass through it. But guess what, the electron
is striped off to flow through the
anode. We explain how this works below.
Polyethylene is multiple ethylene molecules bound together, like so:
H H H H H H H H H
| | | | | | | | |
-C-C-C-C-C-C-C-C-C-
| | | | | | | | |
H H H H H H H H H
In perfluorination the fluorine is substituted for the hydrogen, like so:
F F F F F F F F F
| | | | | | | | |
-C-C-C-C-C-C-C-C-C-
| | | | | | | | |
F F F F F F F F F
Next the polytetrafluoroethylene (PTEE) is sulphonated by the acid HSO2
(sulphonic acid). This adds a side chain SO2
- ion which attracts the hydrogen proton, like so:
F F F F F F F F F
| | | | | | | | |
-C-C-C-C-C-C-C-C-C-
| | | | | | | | |
F F F O F F F F F
|
F-C-F
|
F-C-F
|
O
|
F-C-F
|
F-C-F
|
O=S=O
|
O-
H+
Solphonation is a familiar process used in making detergent, where the chain repels
water (hydrophobic) and clings to the dirt. You notice that this is an "
acid" fuel
cell. The sulphonated fluoroethylene is called
perfluorosulphonic acid. Dupont has
the patent on Nafion, and other fluorosulphonate
ionomers. These compounds, like
Teflon, are tough and chemically resistant. They can be made in thin films. This
reduces the distance between the anode
and cathode,
thus reducing the ohmic
resistance, which causes voltage drops (as so with any electrical or electronic
circuit). They
absorb large quantities of water. They allow H+ ions to pass through without the
electron passing through.
The basic structure of Nafion 117 is:
CF2=CFOCF2CFOCF2CF2SO3H
|
CF
3
This is an illustration of ionic
bonding (see our chemistry/valence discussion in the
carbon section earlier).
REF: Pyle, Walt; Spivak Alan; Cortez, Reynaldo; and Healy, Jim; Making Electricity
with Hydrogen; Home Power Magazine; Issue #35; June/July 1993.
The above article tells you step by step how to build a
fuel cell with Nafion 117. You
can reach Walt Pyle at 510-237-7877. Alan Spivak is at 510-525-4082. Reynaldo Cortez
can be reached at 510-237-9748. Jim Healy can be reached at 510-236-6745. The cost
of Nafion for the project has dropped from $100 to $80 since 1993.
Notice in acid fuel cells
like this, the acid will corrode the less precious metals. This
is a challenge: how to develop
electrodes that use cheaper metals.
Some technical development challenges in fuel cell technology
Getting the best bang for the buck - this is the goal of anything in life.
When it comes to fuel cells, we call it "
efficiency."
Efficiency
was studied by Sadi Carnot (that was his nickname, his real name was Nicolas-leonard-sadi
Carnot) in the time of Napoleon in working with steam
engines around 1824. To understand this, we have the first two laws of thermodynamics.
Thermodynamics studies the state or condition of matter with respect to temperature.
Have you ever wondered how heat pumps work? When gases are expanded they cool; when
gases are compressed, they give off heat. The first law of thermodynamics deals with
energy conservation.
To apply the first law of thermodynamics, when work is done in any system, there are
energy loses in the form of heat. This reduces efficiency unless the heat is
"reversed"
and put back into the system to be used to do work.
In the case of fuel cells,
the work done is moving electrons from the
anode to the
cathode. The heat loss is energy used, but not
to move electrons on the anode.
When the circuit is
open on a fuel cell (called
OCV - open
circuit voltage), the
voltage (measuring potential energy) might be as high as 1.2 volts. When the
circuit is closed
and energy is delivered to a load
(motor, light bulb, boom box, etc.), the
voltage drops to .7 volts. Why?
This gets into the second law of thermodynamics and a concept known as "
entropy."
Entropy
is like a lazy teenager. The more pressure that is applied to get work out of
the lazy teenager, the more the resistance and reaction against moving from a state
of rest. This is not exactly the same as inertia. The teen may be moving or doing
an activity (like video games) and be in a state of equilibrium with that activity.
He/she doesn't respond to those forces that interrupt that state of equilibrium or
direction in his activity (the forces of change). In fact the word
entropy comes
from the Greek word entrope, which means change.
Entropy
is the energy that is not transferred into work in a system, like so:
Energy ® Work + Entropy
REF: Schneider, Eric and Kay, James; Classical Thermodynamics;
Life as a manifestation of the second law of thermodynamics; JK Publications;
Mathematical and Computer Modeling; Volume 19, Number 6-8; Pages 25-48.
http://www.fes.uwaterloo.ca/u/jjkay/pubs/Life_as/text.html#RTFToC3
For Carnot, this loss was manifested in heat, reduced when pistons and moving parts
were well lubricated.
The closed circuit in the
fuel cell measures
the kinetic energy,
rather than the
potential energy. Voltage drops in the fuel cells are caused by:
Polarization
- as protons move from the anode
to the cathode, charge builds up.
This positive charge repels further proton movement, until the proton is united with
oxygen and electrons arriving at the
cathode to neutralize this
polar charge.
Fuel crossing over to the other
electrode. This happens when oxygen shows up at
the anode and hydrogen
gas shows up at the
cathode. Thus, the electron does not flow
from anode to the
cathode, but ends up
flowing from cathode
to cathode. This, we call
a short circuit. No
work is done and all of the energy is
entropy.
Transport holes - when fuel is consumed at the
electrode, until more fuel arrives
at the site, a reaction "hole" exists where no electrons split off from protons on
the anode.
This causes a drop in the potential and
kinetic energy. Pressure and
concentration of pure gas relieve this problem.
Ohmic
losses - This is normal resistance to electron flow. The more electrons
one tries to ram through the circuit,
the lower the voltage drops. The equation is like so:
Voltage = current * resistance
Needless to say, the entropy
theory results in production of heat. If you were to
try to pass a lot of current
through a resisting circuit
at high voltage, you would get
the "flash bulb" effect. The
circuit would overload, smoke, and ultimately burn.
The solution in fuel cells
is to use metals with good conductivity and low resistance.
The electrolyte
provides resistance, so make it thin and reduce the distance of
anode
and cathode.
The problems mentioned above with voltage drop are solved by making the cell parts
smaller. This is a good thing, according the Robert G. Hockaday, founder of Energy Related Devices, Inc.,
because fuel cell
production can use the similar production schemes used in computer
chip manufacture, to which we say, can you see the day when Intel makes
fuel cells?
Reading his company's web page is interesting in and of itself. We found out he blew
up his mother's stove in the 1970's baking his
fuel cellelectrodes.
Notice that he left Los Alamos labs to pursue his dream of imitating nature in the production
of hydrogen. We wonder how much money and profitability has influenced his direction when
you see him lean towards fossil fuel reformation to produce hydrogen. Has he sold out to
avoid the kind of research expense involved to bring nature's methods to production?
We could not find work with algae or bacteria in the site, but the solar discussion was
interesting. See our hydrogen sources section for a larger discussion of these issues.
Follow the URL below to investigate his site
(good through 8/15/2000):
Fuel reforming
Any hydrocarbon (gasoline, methanol, methane, propane, butane) can be reformed to
produce hydrogen and carbon monoxide, like so:
CxHy + xH2)
® (x + y/2) x H2 + xCO
The disadvantage is that there are sulfur compounds in these hydrocarbons that give off
undesirable emissions. These can be removed by using nickel-molybdenum oxide or
cobalt-molybdenum oxide as a
catalyst.
H2S is removed using zinc oxide like so:
Carbon monoxide poisons platinum
catalysts. Later we can apply a water gas shift
at a different temperature to the carbon dioxide
produced in the first reaction, like so:
CO + H2O ® CO2 + H2
For really high temperatures, the hydrocarbon can be oxidized or reformed using oxygen,
rather than water (steam). Get it hot enough, (2,192°F to 2,732°F) and the
reaction occurs without a catalyst.
The reaction is like so:
2CH4 + O2 ®
2CO + 4H2
Steam reacts with pure carbon (such as graphite or coal) to produce hydrogen, like so:
C + H2O ® CO + H2
Another "clean" problem with fuel cells
We have seen how reforming above produces carbon dioxide. Another problem with
fuel cells that use air for an oxygen supply is that when hydrogen is burned in
air, the byproduct is N2O, which causes environmental problems, which
we'll consider in a later policy tab.
Is hydrogen safe?
Most people have heard of the Hindenburg, a big blimp that was filled with hydrogen. It blew up
while in flight. If you are unfamiliar with it, it was a German luxury cruising blimp filled
with 7 million cubic feet of hydrogen. It could go 84 miles an hour and was three football
fields (804 feet) in length. It had a dining salon, lounges, and staterooms. On May 6, 1937, it
crashed in New Jersey after crossing the Atlantic. It had 61 crewmembers and 36 passengers.
36 died.
William D. Van Vorst, a UCLA professor and retired NASA scientist concluded that the
coating of the skin of the Hindenburg blimp, not hydrogen was the cause of the crash.
The cotton skin was treated with iron oxide, cellulose acetate, and aluminum powder was
as explosive as rocket fuel. He concluded this, because the explosion happened
with flames coming down. Hydrogen, being light, burns upward. The explosion was
colored; hydrogen burns clearly. He concludes that hydrogen is no more dangerous than
gasoline.
REF: Bain, Addison and Schmidtchen, Ulrich; Afterglow of a Myth - Why and how the Hindenburg burnt;
Deutscher, Wasserstoff, Verband.
http://www.dwv-info.de/pm/hindbg/hbe.htm
1889 - fuel cell
was named by Ludwig Mond and Charles Langer. They use platinum
catalysts to increase
the reaction rate.
REF: The Natural Gas Fuel Cell; Fuel Cell Commercialization Group;
The Natural Gas Information and Educational Resources website; May 19, 1998.
http://www.naturalgas.org/FUELCELL.HTM
1932 - Francis T. Bacon of Cambridge, England demonstrated an
alkaline
fuel cell,
although others had presented them as early as 1902, but not as serious power producers.
He worked on the catalysts
and used less expensive nickel. In 1959 he used a 5-kilowatt
fuel cell to power a welding machine.
1959 - Harry Karl Ihrig invented the Allis Chalmers 20 hp tractor powered by a
fuel cell.
REF: The Natural Gas Fuel Cell; Fuel Cell Commercialization Group;
The Natural Gas Information and Educational Resources website; May 19, 1998.
http://www.naturalgas.org/FUELCELL.HTM
1963 - NASA used
fuel cells in the Gemini space missions
REF: Walter, Katie; The Unitized Regenerative Fuel Cell;
Lawrence Livermore National Laboratory; University of California, USA; May 1997.
http://www.llnl.gov/str/Mitlit.html
Auto manufacturers got on the bandwagon in the 1960s and have come to the 21st century
with major million and billion dollar commitments to the development of this technology.
Their history is listed on
tab 5 of this section.
