How a Fuel Cell Works

A fuel cell is a device that creates electric power from a chemical reaction involving hydrogen and oxygen.  It is quiet, efficient and emits pure water (H₂O) as an exhaust.  It can be used like a battery that continuously produces power as long as there is a supply of hydrogen gas and oxygen (from the air).

A fuel cell is made up of four basic parts:

1. Hydrogen electrode
2. Proton Exchange Membrane (PEM)
3. Oxygen electrode
4. Circuitry connecting the electrodes

An electrode is a thin piece of metal that conducts electricity very well.  A proton exchange membrane (PEM) is a thin, plastic sheet that is coated on each side with highly dispersed metal particles (usually platinum).  The metal particles act like a catalyst and split apart the positive and negative ions by allowing the positive ions to pass through the membrane but blocking the negative ions.  The two electrodes sandwich the PEM making a flat thin panel.  The size of this panel varies and affects the amount of power that the fuel cell is capable of producing.

When the regenerative fuel cell is producing power it is said to be operating in the “fuel cell” mode.  In this mode, hydrogen is introduced to the hydrogen electrode.  The PEM only allows the positive ions to pass through it.  So it separates the hydrogen gas into positive ions (H⁺) and negative ions (e^-).  The positive ions pass through the PEM to the oxygen electrode.  The negative ions (electrons) are forced to travel through an external circuit to get to the now positive oxygen electrode.  This produces electrical power.  The positive and negative ions meet at the oxygen electrode and react with the oxygen in the air to produce water.  (see figure 1.)

Figure 1.


The Regenerative Fuel Cell

This process is also reversible.  This means that if water and an electric current are supplied to the fuel cell, hydrogen gas can be produced.  A regenerative fuel cell is a completely reversible fuel cell.  When there is power supplied to the unit, it begins “charging” by producing hydrogen gas for later use.  When there is a power need, the process reverses and the fuel cell produces electricity from the stored hydrogen gas.

The regenerative fuel cell is “charging" when it is in hydrolysis mode (figure 2).  Hydrolysis is when water is broken down into oxygen and hydrogen.  In the regenerative fuel cell, water is supplied to the oxygen electrode and electric power is supplied to the circuit.  Once again, the PEM separates the water into hydrogen ions and oxygen.  The positive hydrogen ions pass through the PEM to the hydrogen electrode.  Electrons from the power source react with the hydrogen ions to form hydrogen gas.  The gas is then stored in a tank for later use.

Figure 2.

Fuel Cell Advantages:

• Extremely high efficiencies.
  • 40%-90% if surplus heat is utilized.
• Environmentally friendly.
  • Creates power through a chemical reaction : no emissions.
• Operate on a variety of fuels: hydrogen, natural gas.                                        
• Low operating temperatures (80^oC to 1000^o C).
  • Note: internal combustion engine at 2300^o C.         
• Quiet, small, and can be located in a variety of areas.
• Quick response to load variations (unlike batteries).
• No moving parts.

The regenerative fuel cell can be used just like a battery and it has the following advantages:

• It is more environmentally safe.
• It can produce more power than a battery of the same size.
• The power storage is limited only by the size of the hydrogen storage tank, so it can store a greater amount of power.
• It has quick response to load variations by simply increasing or decreasing the flow rate of hydrogen.
• It is the future!

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