Hydrogen Fuel Cells

A fuel cell is a device that uses hydrogen and oxygen to create electricity. Fuel cells are more efficient than combustion engines and the hydrogen used to power them can come from a variety of sources. If pure hydrogen is used as a fuel, fuel cells emit only heat and water, eliminating air pollutants or greenhouse gases.

Fuel Cell Stack
One of the more common types of fuel cell is the Polymer Electrolyte Membrane (PEM) fuel cell. The PEM fuel cell consists of an electrolyte membrane sandwiched between an anode and a cathode.

The PEM is a thin, solid, organic compound, typically the consistency of plastic wrap and about as thick as 2-7 sheets of paper. This membrane functions as an electrolyte: a substance that conducts charged ions (in this case protons), but does not conduct electrons. This allows the solution to conduct electricity. This membrane must be kept moist to conduct particles through it.

The anode is the electrode at which oxidation (loss of electrons) takes place. In a fuel cell, the anode is electrically negative.

The cathode is the electrode at which reduction (gaining of electrons) takes place. In fuel cell, the cathode is electrically positive.

Flow Plates
Flow plates perform several important functions:
  1. They channel hydrogen and oxygen to the electrodes,
  2. They channel water and heat away from the fuel cell, and
  3. They conduct electrons from the anode to the electrical circuit and from the circuit back to the cathode.

The Chemical Process

Hydrogen fuel (H2) is channeled to the anode, where the catalyst separates the hydrogen’s negatively charged electrons from the positive protons.

The membrane allows the positively charged protons to pass through to the cathode, but not the negatively charged electrons.

The negatively charged electrons must flow around the membrane through an external circuit. This flow of electrons forms an electrical current.

At the cathode, the negatively charged electrons and positively charged hydrogen ions (protons) combine with oxygen to form water (H2O) and heat.

Fuel Cell
The amount of power produced by a fuel cell depends on several factors, including fuel cell type, cell size, temperature at which it operates, and pressure at which the gases are supplied to the cell. A single fuel cell produces less than 1.16 volts – barely enough to run the smallest applications.

Fuel Cell Stacks
To increase the amount of electricity generated, individual fuel cells are combined in series, into a fuel cell “stack.” A typical fuel cell stack may consist of hundreds of fuel cells.

Other types of fuel cells:

Source:   http://www.fueleconomy.gov/feg/fcv_PEM.shtml


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