Technology

 

What is a Fuel Cell?

A fuel cell operates quite like a battery but unlike a battery, a fuel cell does not discharge or require recharging. It produces energy in the form of electricity and heat as long as hydrogen is being supplied. A fuel cell consists of two electrodes with a polymer electrolyte membrane (PEM) sandwiched between two electrodes. Oxygen passes over the cathode and hydrogen passes over the anode, generating electricity, heat and water.

 


The hydrogen atom splits into a proton and an electron; they then take different paths to the cathode. The proton can pass through the PEM. The electrons then create a separate current that can be utilized before they are allowed to return to the cathode, to be joined again with the hydrogen and oxygen to reform to a molecule of water.

The various types of fuel cells

Proton Exchange Membrane (PEM) Efficiency is 40 to 50 percent at about 80 degrees C. Cell output ranges from 500W to 250 kW. The electrolyte is a flexible polymer. Their relatively low operating temperature and flexible electrolyte make them ideal for automotive use.

Alkaline (AFC) Operate at about 70 percent efficiency at temperatures between 150 and 200 degrees C. Cell output range is 300W to 5kW and they use a liquid electrolyte of potassium hydroxide (KOH) and water and can potentially leak.

Molten Carbonate (MCFC) Operate at about 60 to 80 percent efficiency at temperatures of about 650 degrees C. Cell output is about 200 MW. Carbonate ions from the electrolyte are depleted in the reactions and require the injection of additional carbon dioxide.

Phosphoric Acid (PAFC) Efficiency ranges from 40 to 80 percent at about 150 to 200 degrees C. Cell output is around 200 kW. The phosphoric acid electrolyte is corrosive to internal cell parts.

Solid Oxide (SOFC) Operational efficiency is about 60 percent at temperatures of 980 degrees C. Cell output is up to 100kW. The Solid electrolyte is prone to cracking.

How Fuel Cells Work:

Fuel cells produce electricity through an electrochemical reaction within the fuel cell stack using reverse electrolysis, which releases the energy produced as a direct result of the oxidation of hydrogen in the form of electricity.

The reaction combines hydrogen and oxygen to form water vapour, heat and electricity. All of these by-products of the reverse electrolysis reaction can be further utilized by the fuel cell system.

Waste heat can be used for heating and cooling. The water vapour can be captured and re-used for additional hydrogen generation and the electricity is used in an external circuit where it is used by the household.

The benefits of Fuel Cells:

  • Environmentally friendly fuel cells achieve high fuel efficiencies while emitting extremely very low emissions.
  • Fuel cells operate on a wide variety of fuels, using electrochemical reactions. These features make them simple to operate, quiet and extremely reliable.


One advantage of fuel cells is their fuel flexibility. With the correct reforming technology, fuel cells can utilise hydrogen from a wide variety of currently available fossil fuels (e.g. natural gas, methanol, etc.) from fossil fuels. Fuel cells require one natural element as their fuel, hydrogen, the most abundant element on Earth. In addition to fossil fuels, hydrogen can be generated renewably from water and solar.

For video on fuel cells: http://www.youtube.com/watch?v=Dcomfck7xDg&feature=related

For more technical information click on this link: http://www1.eere.energy.gov/hydrogenandfuelcells/fc_publications.html#fc_general

For how they work in cars: http://www.youtube.com/watch?v=QBk1sDculpM&feature=youtube_gdata_player

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