| ABOUT
| CATEGORIES
| Worlds of David Darling |
ADVERTISING | CONTACT |
PEM fuel cell
 |
| A PEM fuel cell consists of a polymer electrolyte
membrane 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 Polymer Electrolyte Membrane (PEM) allows
only the positively charged ions to pass through it to the cathode.
The negatively charged electrons must travel along an external circuit
to the cathode, creating an electrical current. 4. At the cathode,
the electrons and positively charged hydrogen ions combine with oxygen
to form water, which flows out of the cell. |
Polymer electrolyte membrane fuel cells operate at relatively low temperatures, around 80°C (176°F). Low-temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen's electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to carbon monoxide (CO) poisoning, making it necessary to employ an additional reactor to reduce CO in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This also adds cost. Developers are currently exploring platinum/ruthenium catalysts that are more resistant to CO.
PEM fuel cells are used primarily for transportation applications and some stationary applications. Due to their fast startup time, low sensitivity to orientation, and favorable power-to-weight ratio, PEM fuel cells are particularly suitable for use in passenger vehicles, such as cars and buses.
A significant barrier to using these fuel cells in vehicles is hydrogen storage. Most fuel cell vehicles (FCVs) powered by pure hydrogen must store the hydrogen on-board as a compressed gas in pressurized tanks. Due to the low-energy density of hydrogen, it is difficult to store enough hydrogen on-board to allow vehicles to travel the same distance as gasoline-powered vehicles before refueling, typically 300–400 miles. Higher-density liquid fuels, such as methanol, ethanol, natural gas, liquefied petroleum gas, and gasoline, can be used for fuel, but the vehicles must have an on-board fuel processor to reform the methanol to hydrogen. This requirement increases costs and maintenance. The reformer also releases carbon dioxide (a greenhouse gas), though less than that emitted from current gasoline-powered engines.
Related category
• FUEL CELLSSource: U.S. Department of Energy
Also on this site:
Encyclopedia of Science
Encyclopedia of History