| What is a Fuel Cell?
A fuel cell has four basic
components, two electrodes called anode and cathode, one electrolyte and a catalyst or
enzyme between the electrodes and the electrolyte in the center. These components are made
of different kinds of materials in different types of fuel cells. The process of
generating electricity from a fuel cell requires four basic steps. First, hydrogen enters
the fuel cell through the anode electrode. Then, the catalyst splits the electron and
proton apart in the hydrogen and produces a hydrogen ion. (2H2 --> 4H+ + 4e-) After
that, the proton travels to the cathode through the electrolyte while the hydrogen ion
creates a flow of electricity. After the energy has been utilized, the electron is sent
back to the cathode and it is combined with the proton and oxidizes to form a water
molecule (4e- + 4H+ + O2 --> 2H2O).
The table below contains a list and
description of some of the various types of hydrogen fuel cells:
Phosphoric Acid |
This fuel cell is the most commercially developed. It operates at
about 204 degrees C. The normal energy efficiency of this type of fuel cell is around 40%,
but the cell can achieve as high as 85% provided the steam produced from the cell is used
properly. |
|
Proton Exchange Membrane (PEM) or Solid Polymer |
This type of fuel cell is named after the material used for the
electrolyte, polymer membrane. The catalyst of a PEM cell is made of platinum. This type
of cell has the most potential on small applications according to the Department of Energy
of the United States of America. The reasons they have such comments is that this type of
cell can vary its output. This type of fuel cell also operates at a relatively low
temperature, 85 degrees C, when compared with the other types of fuel cells. The
Vancouver-based Ballard Power Systems are currently using PEM fuel cells. |
|
Molten Carbonate |
This is a pretty new technology had its first test and demonstration in
California in 1996. It operates at about 1,200 degrees F. The ability of consuming
coal-based fuel is the unique characteristic of the Molten Carbonate Fuel Cell. |
|
Solid Oxide |
Similar to the PEM fuel cell, this type of fuel cell got its name
from its electrolyte material. The Solid Oxide Fuel Cell uses hard ceramic material for
the electrolyte. This type of fuel cell can generate large amounts of energy at the
efficient rate of 60%, which are suitable for power-plant type of operations. However, the
cell's operating temperature is extremely high, around 1,800 degrees C. |
Alkaline |
NASA uses alkaline Fuel Cells for space missions because it can achieve up to 70%
of fuel-to-electricity efficiency. However, this cell has a big disadvantage, which is the
extremely costly alkaline potassium hydroxide electrolyte. |
Direct Methanol (DMFC) |
Although this is a relatively new technology, it still uses polymer membrane as
its electrolyte. The main difference between a DMFC and PEM fuel cell is that DMFC does
not require pure hydrogen as fuel, and it can consume liquid methanol directly without a
"fuel reformer." The efficiency of this cell is around 40% at 120-190 degrees F.
However, higher efficiency has been achieved at higher temperatures. |
Regenerative |
This is a technology combining solar electrolysis with fuel cells.
Solar electrolysers separate hydrogen from oxygen in water. The oxygen and hydrogen are
combined at the fuel cell, turned back into water and go back to the electrolyser. |
Aluminium Oxygen |
This type of fuel cell uses Aluminium Anodes as fuel, and with the
combination of oxidant, the cell is "air-independent." This cell is best suited
for underwater operations. The energy production of Aluminum Oxygen Semi-Fuel Cells are 3
times, 10 times and 6 to 7 times greater than silver zinc battery, lead acid battery and
NiCad battery respectively. |
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