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About Fuel Cells
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About Fuel Cells

What is a Fuel Cell?

A fuel cell is an electrochemical device that combines hydrogen and oxygen to produce electricity , with water and heat as the by-products. A fuel cell is similar in structure to a battery but it does not run down, nor does it require recharging — as long as hydrogen is supplied, it will continue to operate. The conversion of the fuel (hydrogen) to energy takes place without combustion ; therefore the process is highly efficient , clean and quiet.

Electrochemistry of Fuel Cells
Fuel cells are really a family of technologies. Five major types, characterized by their electrolytes, have been developed: Proton Exchange Membrane (PEMFC) , Alkaline (AFC) , Phosphoric Acid (PAFC) , Molten Carbonate (MCFC) and Solid Oxide (SOFC) . Direct Methanol Fuel Cells (DMFCs) are a type of PEMFC that directly uses methanol as the fuel.
 

Fuel Cell Basics

Fuel cell power systems convert the chemical energy of a fuel and an oxidant directly into electrical energy and heat using electrochemical processes—not combustion. In a fuel cell system, individual fuel cells can be combined in series into a fuel cell "stack" to achieve the desired voltage. The fuel cell "stack" is the principal component of a fuel cell power system. The total fuel cell power system consists of:

  Fuel Cell "Stack" or Fuel Cell Power Section
     
  Balance-of-plant
   
  Fuel Reformer or Processor—to extract hydrogen from the fuel.
  Power Conditioner—to condition DC voltage to meet AC electrical load requirements.

Perhaps the simplest system, a Proton Exchange Membrane Fuel Cell (PEMFC), combines hydrogen fuel with oxygen from the air to produce electricity, water, and heat. This process is essentially the reverse of electrolysis of water. The electricity results from free electrons liberated from hydrogen at the anode flowing through an external electrical circuit before recombining with hydrogen ions and oxygen at the cathode to produce water.

Picture Source: “Fuel Cells – Green Power”, Los Alamos National Laboratory.

A Basic Proton Exchange Membrane Fuel Cell consists of 3 components: an anode (a negative electrode that repels electrons), an electrolyte in the centre, and a cathode (a positive electrode that attracts electrons).

As hydrogen flows into the fuel cell on the anode side, a platinum catalyst facilitates the separation of the hydrogen gas into electrons and protons (hydrogen ions). The hydrogen ions pass through the membrane (the centre of the fuel cell) and, again with the help of a platinum catalyst, combine with oxygen and electrons on the cathode side, producing water. The electrons, which cannot pass through the membrane, flow from the anode to the cathode through an external circuit containing an electric load, which consumes the power generated by the cell.

The voltage from one single cell is about 0.7 volts – just about enough for a light bulb. When the cells are stacked in series, the operating voltage increases to 0.7 volts multiplied by the number of cells stacked.