Fuel cell

A fuel cell is an electrochemical cell (much like a battery) in which fuels are consumed as energy is released.

A fuel cell can be considered as a battery that operates on flowing reactants. Typical reactants are hydrogen on the anode side and oxygen on the cathode side. Batteries consume their reactants and, once these reactants are depleted, must be discarded or recharged with electricity by running the chemical reaction backwards. Fuel cells do not retain the reaction products themselves. They can continue to operate as long as they are supplied with a continuous flow of reactants.

Fuel cells are attractive for their high efficiency and low pollution. They have been suggested for a number of applications, including baseload utility power plants[?], emergency backup generators, off-grid power storage, portable electronics, and vehicles.

Their use is controversial in some applications. The hydrogen typically used as a fuel isn't a primary source of energy. It is usually only a source of stored energy that must be manufactured using energy from other sources. Some critics of the current stages of this technology argue that the energy needed to create the fuel in the first place may reduce the ultimate energy efficiency of the system to below that of highly efficient gasoline internal-combustion engines; this is especially true if the hydrogen is generated from electrolysis of water by electricity. On the other hand, hydrogen can be generated from methane (the primary component of natural gas) with approximately 80% efficiency. The methane conversion method releases greenhouse gases, however, and the ideal environmental system would be to use renewable energy sources to generate hydrogen through electrolysis. Other types of fuel cells don't face this problem. For example, biological fuel cells take glucose and methanol from food scraps and convert it into hydrogen and food for the bacteria.

There are practical problems to be overcome as well. Although the use of fuel cells for consumer products is probable in the near future, most current designs won't work if oriented upside down. They currently can not be scaled to the small size needed by portable devices such as cell phones. Current designs require venting and therefore can not operate under water. They may not be usable on aircraft because of the risk of fuel leaks through the vents. Technologies for safe refueling of consumer fuel cells are not yet in place.

Table of contents 1 Science 2 History 1 The fuel cell industry 2 External links

Science

Fuel cells are electrochemical devices, so they are not constrained by the maximum thermal (Carnot) efficiency as combustion engines are. Consequently, they can have very high efficiencies in converting chemical energy to electrical energy.

In the archetypal example of a hydrogen/oxygen polymer electrolyte membrane (PEM) fuel cell, a proton-conducting polymer membrane separates the anode ("fuel") and cathode sides. Each side has an electrode, typically carbon paper coated with platinum catalyst.

On the anode side, hydrogen diffuses to the anode catalyst where it dissociates into protons and electrons. The protons are conducted through the membrane to the cathode, but the electrons are forced to travel in an external circuit (supplying power) because the membrane is electronically insulating.

On the cathode catalyst, oxygen molecules react with the electrons (which have travelled through the external circuit) protons to form water.

In this example, the only waste product is water vapor.

History

The first fuel cell was developed in the 19th century by British scientist Sir William Grove. A sketch was published in 1843. But fuel cells did not see practical application until the 1960s, where they were used in the U.S. space program to supply electricity and drinking water (hydrogen and oxygen being readily available from the spacecraft tanks). Extremely expensive materials were used and the fuel cells required very pure hydrogen and oxygen. Early fuel cells tended to require inconveniently high operating temperatures that were a problem in many applications.

Further technological advances in the 1980s and 1990s, like the use of Nafion as the electrolyte, and reductions in the quantity of expensive platinum catalyst required, have made the prospect of fuel cells in consumer applications such as automobiles more realistic.

The fuel cell industry

Ballard Power Systems is a major manufacturer of fuel cells and leads the world in automotive fuel cell technology. Ford Motor Company and DaimlerChrysler are major investors[?] in Ballard. As of 2003, the only major automobile companies persuing internal development of fuel cells for automotive use are General Motors and Toyota; most others are customers of Ballard.

United Technologies[?] (UTX[?]) is a major manufacturer of large, stationary fuel cells used as co-generation power plants in hospitals and large office buildings[?].

External links

• Fuel Cells Hydrogen Technology News and Events (http://www.fuelcell-info.com/)
• BBC News, 16 June, 2000: Fuel cells get even cooler (http://news.bbc.co.uk/hi/english/sci/tech/newsid_793000/793485.stm)
• PhysicsWorld: Fuel cells (http://physicsweb.org/article/world/11/7/2)
• PhysicsWorld: Fuel cells: power for the future (http://physicsweb.org/article/world/11/8/11) Quote: "... The high efficiency of fuel cells, which can range from 40% to 70%, and the possibility of improving the overall efficiency of such systems using combined heat and power (CHP) designs would significantly reduce emissions...."