Fuel cell principle:
Discovered in 1839 by an English physicist, Sir William Grove, the fuel cell principle relies on the simple fact that water could be split into hydrogen and oxygen by sending an electric current through it, a process which is called electrolysis. Therefore, by reversing the procedure you could produce electricity and water. He created a primitive fuel cell and called it a “gas voltaic battery”. After experimenting with his new invention, Grove proved his hypothesis. Fifty years later, scientists Ludwig Mond and Charles Langer invented the term “fuel cell” when they attempted to build a practical model to produce electricity.[i]
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The widening of fuel sources decreases certainly the "cleanliness" of the process, by reintroducing carbon emissions, but with no common measure however with the nuisances of internal combustion engines. On the other hand, the reforming considerably increased the interest of fuel cells by enabling hydrogen production processes widely mastered on the industrial sector.
Different types of fuel cells
The family of fuel cells is quite large. Fuel cells are usually classified on the type of electrolyte they use and their operating temperatures. Some fuel cells are more suitable for a stationary use, while others may be used for small portable applications or for powering cars. There are 6 main types of fuel cells:
Polymer exchange membrane fuel cell (PEMFC)
It is the most likely candidate for transportation applications since it has a high power density and a relatively low operating temperature (ranging from 60°C to 80°C). The low operating temperature implies that the fuel cell warms up quickly and swiftly begins to generate electricity. The US department of energy focuses on this type of fuel cell for transportation applications.
Solid oxide fuel cell (SOFC)
It is best suited for large-scale stationary power generators that could provide electricity for factories or towns. It operates at very high temperatures (between 700 and 1,000°C). This high temperature creates a reliability problem, since parts of the fuel cell can break down after cycling on and off repeatedly. This type of fuel cell is however very stable when in continuous use and has demonstrated the longest operating life of any fuel cell under certain operating conditions. The high temperature also produces steam, which can be channeled into turbines to generate more electricity. This process is called co-generation of heat and power (CHP) and it improves the overall efficiency of the system.
Alkaline fuel cell (AFC)
It is one of the oldest designs, in the US, space programs have used them since the 1960s. This type of fuel cell is very susceptible to contamination and therefore requires pure hydrogen and oxygen. It is also very expensive, so this type of fuel cell is unlikely to be commercialized.
Molten-carbonate fuel cell (MCFC)
It is also best suited for large stationary power generators. Since it operates at at 600°C, it generates steam that can be used to generate more power. Since they have a lower operating temperature than the SOFCs, it makes the design a little less expensive.
Phosphoric-acid fuel cell (PAFC)
The phosphoric-acid fuel cell has potential for use in small stationary power-generation systems. It operates at a higher temperature than PEMFCs, therefore has a longer warm-up time. This makes it unsuitable for use in cars.
Direct-methanol fuel cell (DMFC)
Methanol fuel cells are comparable to a PEMFC in regards to operating temperature, but are not as efficient. Also, the DMFC requires a relatively large amount of platinum to act as a catalyst, which...