Fuel cell How does it work?

A fuel cell generates electrical power by continuously converting the chemical energy of a fuel into electrical energy by way of an electrochemical reaction. The fuel cell itself has no moving parts, making it a quiet and reliable source of power. Fuel cells typically utilize hydrogen as the fuel, and oxygen (usually from air) as the oxidant in the electrochemical reaction. The reaction results in electricity, by-product water, and by-product heat.

Because the fuel is converted directly to electricity, a fuel cell can operate at much higher efficiencies than internal combustion engines, extracting more electricity from the same amount of fuel.

When hydrogen gas is introduced into the system, the catalyst surface of the membrane splits hydrogen gas molecules into protons and electrons. The protons pass through the membrane to react with oxygen in the air (forming water). The electrons, which cannot pass through the membrane, must travel around it, thus creating the source of DC electricity.  

Individual fuel cells can be then combined into a fuel cell "stack". The number of fuel cells in the stack determines the total voltage, and the surface area of each cell determines the total current. Multiplying the voltage by the current yields the total electrical power generated.

• The PEMFC stack is the heart of the fuel cell system. It is made up of a membrane electrode assembly (MEA) sandwiched between two gas diffusion layers (GDLs) with bipolar plates on each side.
  
• The reformate arriving from the CO cleanup system feeds the fuel side of the fuel cell. The hydrogen in the fuel passes through the GDL, which typically serves three functions within a PEM fuel cell:
  

1. Diffuse the reactant gases across the surface of the membrane
2. Manage the water around the membrane
3. Provide a highly conductive path between the membrane and bipolar plate

The MEA ionizes the hydrogen, passes the hydrogen ions, and combines the ions with oxygen to form water. MEA catalysts are typically made of precious metals such as platinum. The improvement in platinum application to the MEA is one major reason for decreasing the costs of a fuel cell.

• The fuel processor portion of a fuel cell system has two operating components.
  

1. The fuel reformer processes a hydrocarbon fuel, such as natural gas, into a hydrogen-rich gas known as reformate. Reformate contains heavy concentrations of CO so a CO cleanup system is applied to reduce the CO concentrations to acceptable levels (under 50 ppm).
   
2. The carbon monoxide (CO) cleanup unit.
   

• The last step is the power conditioner. The power conditioner first converts the low-voltage direct current (DC) produced by the PEMFC to a high-voltage alternating current (AC).
  
• Batteries are used to ensure that power surges from such things as air conditioner start-ups can be handled.
  Batteries also meet any extended peak period of demand, which is higher than stack peak output.

Graphic by Marc Marshall, Schatz Energy Research Center

Benefits include:
1. Zero greenhouse gas or toxic emissions from fuel cells
2. Hydrogen is an abundant, ubiquitous source of energy
3. Hydrogen is a non-toxic fuel
4. Light molecular weight of hydrogen means it dissipates quickly reducing risk of concentrated and long-lasting fire
5. Scalable size of fuel cells allows them to be used in thousands of applications
6. Can be used for stationary and mobile uses
7. Reduced dependence on fuel from politically volatile regions

Standalone Fuel Cell Controller with 220VAC inverter driver at PBP Fuel Cell Technology Center

Click to enlarge