How Fuel Cells Work
The Benefits of Fuel Cells
Types of Fuel Cells
Portable Fuel Cell(picture taken from http://www.nfcrc.uci.edu/fuelcellinfo_index.htm)
|Efficiency of Vehicles
Pictures of Different Fuel Cells
A fuel cell is a lot like a battery. It has two electrodes where the reactions take place and an electrolyte which carries the charged particles from one electrode to the other. In order for a fuel cell to work, it needs hydrogen (H2) and oxygen (O2). The hydrogen enters the fuel cell at the anode. A chemical reaction strips the hydrogen molecules of their electrons and the atoms become ionized to form H+. The electrons travel through wires to provide a current to do work. The oxygen enters at the cathode, usually from the air. The oxygen picks up the electrons that have completed their circuit. The oxygen then combines with the ionized hydrogen atoms (H+), and water (H2O) is formed as the waste product which exits the fuel cell. The electrolyte plays an essential role as well. It only allows the appropriate ions to pass between the anode and cathode. If other ions were allowed to flow between the anode and cathode, the chemical reactions within the cell would be disrupted.
The reaction in a single fuel cell typically produces only about 0.7 volts. Therefore, fuel cells are usually stacked or connected in some way to form a fuel cell system that can be used in cars, generators, or other products that require power.
The reactions involved in a fuel cell are as follows:
Cathode side (a reduction reaction):
O2 + 4H+ + 4e- => 2H2O
Net reaction (the "redox" reaction):
2H2 + O2 => 2H2O
Like anything else in the world fuel cells are not perfect. They face several limitations
that hold the fuel source back. Probably the biggest problem faced is that in order for fuel
cells to work a source of hydrogen is needed. As long as there is hydrogen available to the fuel cell, the fuel cell will be able to operate (Daugherty and Hoffman, 10-11). Hydrogen is not, however, something you can go get at
your local grocery market or gas station. So far there are no hydrogen gas stations. The
main reason for this is that hydrogen is difficult to store and distribute.
There have been solutions proposed to counter this limitation. A "reformer" has been
considered a solution because it can convert hydrocarbons (fossil fuels) or alcohol fuels (such as methanol or ethanol) into hydrogen.
In otherwords, it allows a convenient source of hydrogen. Below shows two possible pathways of the fuel for a fuel cell and the reformer's position in converting the fossil fuels to hydrogen.
The other problem with fuel cells is that they are expensive. It is complicated to be able to build inexpensive, reliable, and efficient fuel cells. The membrane of a fuel cell is used as an electrolyte in order to conduct protons. One especially large stumbling block is the designing of appropriate proton-exchange membranes for fuel cells. The problem is it is difficult to find a membrane that is impermeable to hydrogen and oxygen, while still being an efficient conductor of protons. Another major problem with membranes is that they become soggy, which makes them weaker and unproductive. Gore-Tex, a water-repelling mesh normally used in sport clothing, is both strong and porous which makes it a great ion exchange membrane while not becoming soggy. For this reason, it is one leading candidate for the fuel cell membrane (Voss, 684).
Phosphoric Acid Fuel Cell-Is available today -There have been over 200 fuel cells of this type already installed all over the world -in hospitals, nursing homes, hotels, schools, utility power plants -Provides 40% efficiency -Operates at temperatures around 400o F
Proton Exchange Membrane (PEM) Fuel Cell-Operates at relatively low temperatures -Oxygen is pumped into cathode from air for reaction with hydrogen -The main types used in vehicles
Molten Carbonate Fuel Cell-Promises high fuel-to-electricity efficiencies -Operates at 1,200o F
Solid Oxide Fuel Cell-Could be used in big, high-power applications -industrial -large scale, central electricity-generating situations
Alkaline Fuel Cell-Used by NASA -Since 1960s -Power-generating efficiencies of up to 70% -Too expensive right now to be built for public use
Direct Methanol Fuel Cell-Polymer membrane as electrolyte -Anode catalyst draws the hydrogen directly from liquid methanol (no reformer needed) -40% efficiency (higher at higher temperatures)
Regenerative Fuel Cell-Water separated into hydrogen and oxygen by solar-powered electrolyser -Hydrogen and oxygen fed into fuel cell -Products: electricity, heat, and water -Water is then recycled through the system -Being researched by NASA
For more information on fuel cell types...
Fuel Cell powered -Fuel cell engines are capable of utilizing up to 60% of the power generated if the hydrogen is directly converted to electricity -without pure H2 efficiency drops to 30-40% -With all sources of energy loss accounted for, the overall efficiency is 24-32% -15-25% energy loss from converting methanol or gasoline to hydrogen -The 10-20% increase in weight of the vehicle causes more energy to be used (Ogden et al., 6). Gas powered -Internal combustion engines only utilize about 25% of the power generated -main loss is due to exhaust = wasted energy Battery powered -72% efficiency just accounting for battery -If account for how electricity for a battery is made, overall efficiency is 26% -fossil fuels burned in powerplant are needed in order to charge battery
Iceland is set to create the world's first hydrogen economy. In February of 1999 they made a $1 million joint venture called the Icelandic New Energy. This was set up to promote increased use of renewable resources to produce hydrogen. The Icelandic government has set a goal to make the full transition to hydrogen energy between the years of 2030 and 2040. Other places around the world such as Canada and Germany have shown uses of hydrogen as energy. The future of hydrogen as a fuel is so conceivable that by the year 2050 the world may be considered to be in the Hydrogen Age (Dunn, 97).
There also have been other uses for fuel cells. Fuel cells have been used in watches, prototype homes, and space craft. To see different types of fuel cell use click the following link:
Links for Fuel Cells
|Origins||How they work|
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