Ebiz247.com Fuel Cell Technology

What is a Fuel Cell?
A proton exchange membrane fuel cell is an electrochemical device in which the energy of a chemical reaction is converted directly into electricity.

By combining hydrogen fuel with oxygen from air, electricity is formed, without combustion of any form. Water and heat are the only by-products when hydrogen is used as the fuel source.

Although hydrogen is considered the primary fuel source for fuel cells, the process of fuel reforming allows for the extraction of hydrogen from other fuels including methanol, natural gas, petroleum, or renewable sources. Unlike a battery, a fuel cell does not run down or require recharging; it operates as long as a fuel is supplied.

Fuel Cell History
Fuel cells were invented in 1839 by Sir William Grove, and were first used in practical applications in the 1960s to provide electricity on spacecraft in the Gemini and Apollo space programs.

During the 1970s, fuel cell technology was developed for systems on earth. And during the 1980s, it began to be tested by utilities and automobile manufacturers.

There are several types of fuel cells, distinguished by the type of electrolyte material used. The predominant types of fuel cells include the following:

Alkaline Fuel Cells
Alkaline fuel cells have been used since the mid-1960s by NASA in the Apollo and space shuttle programs, to power electrical systems on spacecraft.

They were considered appropriate for small-scale aerospace and defense applications. However, their use in commercial applications is limited because they must operate with pure hydrogen and with pure oxygen, or air from which the carbon dioxide has been removed.

Phosphoric Acid Fuel Cells
Phosphoric acid fuel cells have been field tested since the 1970s. They are the most developed fuel cell technology for stationary power applications, with existing installations in buildings, hotels, hospitals, and electric utilities in Japan, Europe, and the United States.

The principal use of these systems is expected to be mid-to-large stationary power generation applications.

However, the corrosive liquid electrolyte and high operating temperature (200 degrees Celsius) require complex system design and negatively impact operating life and cost.

Molten Carbonate Fuel Cells
Molten carbonate fuel cells operate at very high temperatures (650 degrees Celsius) that allow them to use fuel directly without the need for a fuel processor.

Their system design is more complex than phosphoric acid fuel cells due to their higher operating temperature and their utilization of a molten electrolyte. They require significant time to reach operating temperature and to respond to changes in electricity demand, and therefore are best suited for the provision of constant power in large utility applications.

They have been built in small numbers in the United States and Japan and a prototype 1.8-megawatt power plant has been demonstrated in the United States.

Solid Oxide Fuel Cells
Solid oxide fuel cells operate at extremely high temperatures (700 degrees Celsius - 1,000 degrees Celsius). As a result, they can tolerate relatively impure fuels, such as those obtained from the gasification of coal.

Their relatively simple design (because of the solid electrolyte and fuel versatility), combined with the significant time required to reach operating temperature and to respond to changes in electricity demand, make them suitable for large to very large stationary power applications. They have been demonstrated in laboratory settings and in early field trials.

Proton Exchange Membrane (PEM) Fuel Cells
PEM fuel cells use solid polymer membrane (a thin plastic film) as an electrolyte. They are compact and produce a powerful electric current relative to their size.

The first practical application for PEM fuel cells was in the Gemini space program. Most automakers believe that PEM fuel cells are the only fuel cell appropriate for providing primary power on-board a vehicle.

PEM fuel cells deliver higher power density, resulting in reduced weight, cost and volume and improved performance. An immobilized electrolyte also simplifies sealing in the production process, reduces corrosion, and provides for longer cell and stack life.

PEM fuel cells operate at low temperatures (less than 100 degrees Celsius), allowing faster start-ups and immediate responses to changes in the demand for power. They are ideally suited to transportation and smaller stationary applications. PEM fuel cells have been demonstrated in systems ranging in size from 1 watt to 250 kW.

See how the Ballard PEM Fuel Cell System works.
(Information courtesy of Ballard Power Systems, Inc .)