alkaline fuel cell
Alkaline fuel cells (AFCs) were one of the first fuel
cell technologies developed, and they were the first type widely used
in the U.S. space program to produce electrical energy and water on-board
spacecrafts. These fuel cells use a solution of potassium hydroxide in water
as the electrolyte and can use a variety
of non-precious metals as a catalyst at the anode and cathode. High-temperature AFCs operate
at temperatures between 100°C and 250°C (212°F and 482°F).
However, newer AFC designs operate at lower temperatures of roughly 23°C
to 70°C (74°F to 158°F).
|An alkaline fuel cell consists of an alkaline electrolyte,
typically potassium hydroxide (KOH), sandwiched between an anode (negatively
charged electrode) and a cathode (positively charged electrode). The
processes that take place in the fuel cell are as follows: 1. Hydrogen
fuel is channeled through field flow plates to the anode on one side
of the fuel cell, while oxygen from the air is channeled to the cathode
on the other side of the cell. 2. At the anode, a platinum catalyst
causes the hydrogen to split into positive hydrogen ions (protons)
and negatively charged electrons. 3. The positively charged hydrogen
ions react with hydroxyl (OH-) ions in the electrolyte
to form water. 4. The negatively charged electrons cannot flow through
the electrolyte to reach the positively charged cathode, so they must
flow through an external circuit, forming an electrical current. 5.
At the cathode, the electrons combine with oxygen and water to form
the hydroxyl ions that move across the electrolyte toward the anode
to continue the process.
AFCs' high performance is due to the rate at which chemical reactions take
place in the cell. They have also demonstrated efficiencies near 60% in
The disadvantage of this fuel cell type is that it is easily poisoned by carbon dioxide (CO2).
In fact, even the small amount of CO2 in the air can affect this
cell's operation, making it necessary to purify both the hydrogen and oxygen used in the cell. This purification process is costly. Susceptibility
to poisoning also affects the cell's lifetime (the amount of time before
it must be replaced), further adding to cost.
Cost is less of a factor for remote locations, such as space or under the
sea. However, to effectively compete in most mainstream commercial markets,
these fuel cells will have to become more cost-effective. AFC stacks have
been shown to maintain sufficiently stable operation for more than 8,000
operating hours. To be economically viable in large-scale utility applications,
these fuel cells need to reach operating times exceeding 40,000 hours, something
that has not yet been achieved due to material durability issues. This obstacle
is possibly the most significant in commercializing this fuel cell technology.