For decades, converting primary energy sources into useful forms of energy has been of great interest to governments, private businesses, and academic institutions. These primary energy sources include non-renewable sources such as oil, natural gas, and coal, and renewable sources such as solar and wind. Renewable energy is friendly to our environment since the others cause air pollution by releasing a great deal of carbon dioxide gas. This carbon dioxide gas traps radiation coming from sunlight, which in turn becomes heat, causing the earth's temperature to rise, thus the infamous greenhouse effect and global warming. It is obvious that we need energy sources that work without harming the environment. A promising candidate for this purpose is fuel cells. A fuel cell is a device that converts chemical energy directly to electrical energy without the thermal combustion of the fuel.

Fuel cells are very promising chemical energy conversion devices. Though the first fuel cell was made by William Grove in 1839, they're just now being explored as a real energy alternative (1). Let's take a look at how they work: in a fuel cell, electricity is generated by the reaction of hydrogen and oxygen, which forms water. They are similar to batteries and internal combustion engines (ICEs): just as in a combustion engine, where fuel is oxidized, the oxidization of hydrogen generates energy. They'll work as long as fuel is provided.

Despite these similarities there are some differences that make fuel cells more attractive than batteries and ICEs. A fuel cell works more efficiently and quietly than engines do. When hydrogen is used as fuel, power and drinking water are produced as by-products (2). Having safe by-products answers our concerns regarding older power sources. A battery is dead if it is not re-chargeable; however a fuel cell can be continually reused.

Fuel cells are generally defined by the type of electrolyte used in the cell, and they operate at different temperatures. Alkaline fuel cells (AFCs), proton exchange membrane fuel cells (PEMFCs), and direct methanol fuel cells (DMFCs) are called low-temperature fuel cells. Phosphoric acid fuel cells (PAFCs) are an intermediate-temperature fuel cell. Molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs) are called high-temperature fuel cells (3, 4).

They have been mainly used for stationary, transportation, and portable applications. Since the need for electricity in daily life has dramatically increased, reliable and efficient power supplies have become necessary. Over 2,000 stationary fuel cell systems have been built in hotels, schools, and hospitals. Stationary power generation is considered more commercialized among the other fuel cell applications. Today, these systems have reached an efficiency of 40% when a hydrocarbon is used as fuel. Fuel cell systems are also used in telecommunication systems, and these cells provide power between 1 and 5 kW (5).

Fuel cells have been identified as the most probable alternative power source for transportation applications in place of internal combustion engines (ICEs). There are two distinct features of fuel cells that make them a better choice than ICEs. First, their carbon dioxide gas emissions are nearly zero. Second, fuel cells are much more efficient than ICEs – about two to three times (6). Ballard Power Systems have been developing zero-emission-vehicles by using PEMFCs, which have low operating temperatures and a higher power density.

NASA decided to use fuel cells on American spacecrafts in the 1960s. The advantage of using them in spacecraft was that while they were generating electric power, they produced drinkable water for the astronauts. A fuel cell was used as an integral part of the power supply PEMFCs (1kW) in the Gemini crafts and AFCs (1kW) in the Apollo crafts, both of which were a part of NASA's human spaceflight programs (6).

Portable applications of fuel cells offer electrical power when reaching the electrical grid is not possible. When they are used as power sources outdoors, they help to avoid air and noise pollution (4). Because these portable fuel cells are lighter and more durable than batteries, they have been considered as alternative power sources for mobile phones, laptop computers, and some electronic devices (5). They are also used by the military in battle. A 4 kW PEM generator was built for the U.S. military by Intelligent Energy Ltd., out of Europe (7). Since direct methanol fuel cell systems are much lighter than the indirect systems, they are mostly used as portable power systems.

Although fuel cells have benefits when compared to other power sources, they are not widely used because of their high cost. In 2010, the Energy Information Administration released that the cost of fuel cells is $6.83 per installed watt, which is almost 7 times more expensive than a natural-gas turbine generator plant (8). In 2008, the Honda Clarity produced one of the first hydrogen-powered automobiles; these require very expensive catalysts: platinum (9). A catalyst makes the chemical reactions occur faster. Platinum is still the best catalyst, so this explains the prohibitive cost. A cheaper substitute for platinum is needed for use in automobiles. Another problem is that hydrogen is widely used as fuel for transportation applications. Until there is a sufficient hydrogen infrastructure, car manufacturers will find it hard to mass produce cars that use fuel cells.

Cetin is a freelance science writer.

References
1. Grove, W. R. (1839). On voltaic series and the combination of gases by platinum. Philosophical Magazine and Journal of Science, Series 3,14, 127-130.
2. Hoogers, G. (2003). Fuel Cell Technology Handbook. Boca Raton, FL: CRC Press.
3. Mekhilef, S., Saidur, R., Safari, A. (2012). Comparative study of different fuel cell technologies. Renewable and Sustainable Energy Reviews 16, 981-989.
4. Gencoglu, M. T., Ural, Z. (2009). Design of a PEM fuel cell system for residential application. International Journal of Hydrogen Energy 34, 5242-5248.
5. Andujar, J., Segura, F. (2009). Fuel cells: History and updating. A walk along two centuries. Renewable and Sustainable Energy Reviews 13, 2309-2322.
6. Iovine, John. "Fuel Cells.(composition, energy-generating processes and industry developments and innovations)." Poptronics. Poptronix, Inc. 2001. Retrieved May 17, 2012 from High Beam Research: http://www.highbeam.com/doc/1G1-69015426.html
7. Cowey, K., Green, K., Mepsted, G., Reeve, R. (2004). Portable and military fuel cells. Current Opinion in Solid State and Materials Science 8, 367-371.
8. Administration, U. E. (2010, November). Updated Capital Cost Estimates for Electricity Generation Plants. Retrieved from http://205.254.135.24/oiaf/beck_plantcosts.
9. Muller, R. A. (2012). Energy for Future Presidents: The Science Behind The Headlines. New York: W.W. Norton Company, Inc.

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