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Fuel Cells

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Fuel Cell

What is a Cell?

A cell is a device that generates electricity through a chemical reaction.

What is a Wet Cell and a Dry Cell?

A wet cell is a device that produces electricity through a chemical process using the chemicals (electrolyte) present within it in a liquid form.

A dry cell is a device that produces electricity through a chemical process using the electrolyte present in it in a paste (dry) form.

What is a Fuel Cell?

A fuel cell is a device that generates electricity by chemical reactions. A fuel cell has two electrodes – Positive (cathode) and negative (anode). The chemical reactions take place at these electrodes. It is different from the dry cell as the fuel for the fuel cell is continuously supplied from outside the cell, and not stored within the fuel cell.

As long as a fuel cell is supplied with hydrogen and oxygen, it will generate electricity.

Every cell has an electrolyte. This carries the electrically charged particles from one electrode to the other. There are also catalysts which are added to speed up the chemical reactions at the electrodes.

The fuel cell generates a small amount of direct current (DC).

What fuel does the Fuel Cell use?

The basic fuel of the fuel cell is Hydrogen. Oxygen is also required by fuel cells to function.

What is the exhaust of a Fuel Cell?

Hydrogen and Oxygen combine to form water which is the exhaust of the fuel cell. Thus fuel cells generate electricity with no pollution.

How do Fuel Cells Work?

Anode end:

Hydrogen atoms enter a fuel cell at the anode. Here a chemical reaction removes electrons from the Hydrogen atoms. The atoms without the electrons are called Hydrogen Ions. ( [H]+ ).

These hydrogen ions carry a positive electrical charge and move towards the Cathode inside the fuel cell through the electrolyte.

The electrons are negatively charged. The electrons that are removed from the Hydrogen atom at the Anode travel through electric wires outside the fuel cell.

The electric wires connect the anode through the “Load” to the cathode outside the Fuel cell. The “load” is the work the electricity is supposed to do – like a fan, bulb, motor etc.

Cathode end:

The Hydrogen ions reach the Cathode from the Anode through the electrolyte. Here they combine chemically with Oxygen atoms and the electrons that have travelled (to complete the electric circuit) through the electric wires.

(In certain types of cells, the Oxygen atoms pick up electrons at Cathode and thereafter travel through the electrolyte inside the fuel cell, to the anode, to combine with the hydrogen ions.)

It is essential that the electrons travel through the electrical wires outside the fuel cell only. It should not flow directly inside the fuel cell, as it will stop the fuel cell from functioning.

To control the flow of appropriate ions / electrons between the anode and cathode, the electrolyte plays a major role. Fuel cells are mainly differentiated by the different types and properties of electrolyte used in them.

What are the different types of Fuel Cells?

Prototypes of many types and sizes of fuel cells have been developed in the search for greater efficiency. They are mainly different with respect to the type of electrolyte and the design of their electrodes.

Main electrolyte types are:

Liquid Electrolyte

  • Alkali Fuel Cells: operate on compressed hydrogen and oxygen. They generally use Potassium Hydroxide (KOH) solution as electrolyte. They require pure hydrogen fuel, and their platinum electrode-catalysts are expensive.
  • Molten Carbonate Fuel Cells (MCFC): use high-temperature salt carbonates (CO3) (eg. Sodium Carbonate) as the electrolyte. Their electrode-catalysts are of Nickel, which are comparatively inexpensive. But their high temperature sets limits to the materials and their safe uses. Also, carbonate ions from the electrolyte are used up, requiring injection of Carbon Dioxide to compensate the usage.
  • Phosphoric Acid Fuel Cells (PAFC): use phosphoric acid as the electrolyte. It is a corrosive acid, hence Platinum electrode-catalysts, and other internal parts able to withstand the corrosion are needed.

Solid Electrolyte

  • Proton Exchange Membrane (PEM) Fuel Cells work with a polymer electrolyte in the form of a thin, permeable sheet, which will not leak or crack. They operate at a low enough temperature making them suitable for homes and cars. The fuels must be purified, and also platinum catalyst is required thus raising operating costs.
  • Solid Oxide Fuel Cells (SOFC) use a hard, ceramic compound of metal (like calcium or zirconium) oxides as electrolyte. Operating temperatures are about 1,000 degrees C, which limits applications of SOFC units. They also tend to be of large size.

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