Inside a Fuel Cell

Inside a Fuel Cell

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Description: The red Hs represent hydrogen molecules (H2) from a hydrogen storage tank. The orange H+ represents a hydrogen ion after its electron is removed. The yellow e- represents an electron moving through a circuit to do work (like lighting a light bulb or powering a car).

The green Os represent an oxygen molecule (O2) from the air. The blue drops at the end are for pure water--the only byproduct of hydrogen power.

 
Author: The University of Vermont  | Visits: 279 | Page Views: 427
Domain:  Green Tech Category: Battery & Fuel Cell 
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Contents:
Inside a Fuel Cell
The red Hs represent
hydrogen molecules (H2)
from a hydrogen storage
tank.
The orange H+ represents a
hydrogen ion after its electron
is removed.
The yellow e- represents an
electron moving through a
circuit to do work (like lighting
a light bulb or powering a
car).
The green Os represent an
oxygen molecule (O2) from
the air.
The blue drops at the end are
for pure water--the only
byproduct of hydrogen power.

Types of Fuel Cells
-Alkaline•

Operate on compressed hydrogen
and oxygen.



Uses an alkaline electrolyte such
as potassium hydroxide.



Efficiency is about 70 percent, cell
output being 300 watts-5 kW



Originally used by NASA on space
missions, specifically in Apollo to
provide electricity and drinking
water.



It is now finding applications in
hydrogen-powered vehicles.

Molten Carbonate


The molten carbonate fuel cell
uses a molten carbonate salt as
the electrolyte. It has the
potential to be fueled with coalderived fuel gases or natural gas.



Efficiency ranges from 60-80
percent with an output of 2 MW.



They operate at around 1,200
degrees Fahrenheit, making them
too hot for home use.

Phosphoric Acid


A phosphoric acid fuel cell (PAFC)
consists of an anode and a
cathode made of a finely
dispersed platinum catalyst on
carbon paper, and a silicon
carbide matrix that holds the
phosphoric acid electrolyte.



This is the most commercially
developed type of fuel cell and is
being used in hotels, hospitals,
and office buildings. The
phosphoric acid fuel cell can also
be used in large vehicles, such as
buses.



Efficiency is 40-80 percent with
outputs of 200kW

Proton Exchange Membrane


The proton-exchange membrane
(PEM) fuel cell uses a
fluorocarbon ion exchange with a
polymeric membrane as the
electrolyte.



The PEM cell appears to be more
adaptable to automobile use than
the PAFC type of cell. These cells
operate at relatively low
temperatures and can vary their
output to meet shifting power
demands.



Efficiency is about 40 to 50
percent with outputs generally
ranging from 50 to 250 kW

Solid Oxide


Solid oxide fuel cells (SOFC)
currently under development use
a thin layer of zirconium oxide as
a solid ceramic electrolyte, and
include a lanthanum manganate
cathode and a nickel-zirconia
anode.



This is a promising option for
high-powered applications, such
as industrial uses or central
electricity generating stations.



Efficiency is about 60 percent
with outputs of 100kW

What do you get when
you cross a fuel cell,
an ear of a corn and a
fuel injector from a
stray jalopy?

Ethanol as a Fuel Source
• Ethanol is produced by converting biomass like
cornstarch, sugarcane, sugar beets, and some trees
and grasses to sugar, then fermenting it.


In the United States each year, approximately 2 billion
gallons are added to gasoline to increase octane and
improve the emissions quality of gasoline

It's not cheaper than natural gas or coal...
but it's cleaner, and renewable
-Lanny Schmidt

Ethanol and Fuel Cells


Though hydrogen is the most abundant element on Earth, most
of it is locked up with other elements in forms such as
hydrocarbons and water. It takes a lot of energy to get significant
quantities of hydrogen from water alone, so the most practical
sources from which to liberate hydrogen are fossil fuels such as
natural gas, diesel fuel or gasoline. But using fossil fuels as a
hydrogen source removes some of the “green” appeal of fuel
cells.



University of Minnesota’s Lanny Schmidt was able to produce
hydrogen from ethanol after two simple adjustments to a process
already used to get hydrogen from methane, natural gas and
gasoline.

•Ethanol is fairly flammable, and the process of extracting hydrogen from ethanol destroys
the catalyst traditionally used to extract hydrogen from hydrocarbons like oil.
•The first step was to use an automotive fuel injector to vaporize an ethanol-water mix.
The second required altering the composition of the reactor’s ceramic catalyst material,
a combination of the elements rhodium and cerium, for the vaporized ethanol to pass
through and be converted

Why Ethanol is better…


Conversion of biomass materials such as ethanol into
hydrogen is a more cost-efficient method to power fuel
cells.



“Ethanol in car engines is burned at 20% efficiency
because you have to remove the water first. But if you
use ethanol to produce hydrogen, the efficiency is 50 to
60% because you don’t need to remove the water.
Hydrogen comes from the ethanol and the water.”



Ethanol is relatively easy to make, transport and store,
and it's renewable.



Ethanol reduces our dependence on foreign oil because it
can be produced domestically.



Ethanol is low in reactivity and high in oxygen content,
making it an effective tool in reducing ozone pollution.

Why it hasn’t
happened yet…
• “We’re not going to be switching tomorrow, because there’s not
enough corn out there. If you took it all, you could replace maybe 40
percent of our petroleum needs."
• The energy that goes into raising corn and making ethanol makes it
less attractive than natural gas as a source for hydrogen. (It's only if
you make the ethanol from a cellulosic material with not much
energy going into it that it becomes even plausible as an option for
hydrogen)
• The potential for the new reactor, in its current form, is also
restricted by an existing fossil-fuel dependent infrastructure.