When the anode and cathode are connected with a conductor, the electrons will move around the separator to the cathode, which is exposed to the oxidizer. The chemical reaction is completed; water is created as the byproduct. An electrical load can be connected between the anode and cathode, and therefore work can be done. This is what allows the fuel-cell to be a power source.
It's important to note that this is an exothermic chemical reaction, which means that a substantial amount of heat is given off.
The potential between anode and cathode is on the order of 0.7V; and so just as in the case of batteries or photo-voltaic cells, the fuel-cells can be connected together in series and parallel, making a system with higher-voltage and greater current capability.
The type of fuel-cell that uses pure hydrogen for the fuel is known as the proton-exchange membrane fuel-cell. (The proton-exchange membrane makes up the separator I referred to above.). There is another type of PEMFC that uses other hydrocarbons as fuel; the waste byproducts are then CO2 and water. (More on those below.) Operating temperature of a PEMFC is between 50 and 220 degrees Celsius.
One key component to a PEMFC is the catalyst, which is typically platinum or palladium. There is another type of fuel-cell, known as a solid-oxide fuel cell (or SOFC) that operates at a much higher internal temperature — 600 to 1000 degrees C. One advantage is that it does not need the catalyst on either the anode or cathode. The separator (as the name suggests) is ceramic. At these high temperatures, disassociated oxygen ions will move through the ceramic to oxidize the fuel on the anode side. Again, water is a byproduct. Connecting the cathode and anode together with a conductor allows electrons to flow; they can be used to do work just like any other electrical generator.
As I mentioned above, it isn't necessary to use pure hydrogen as fuel for a PEM fuel-cell.
Some manufacturers have worked to develop PEMFCs that use methanol as the fuel source. Methanol can be used to generate about 4.4kWh per liter of fuel. However, Lilliputian Systems of Wilmington, MA, has spent five years developing a matchbook-size SOFC that uses butane as its fuel. Butane, according to Lilliputian, is a better source of energy, since you can generate about 7.4kWh of power with one liter.
They make use of the intense heat to crack the butane molecules into hydrogen and carbon. The entire SOFC is enveloped in glass under a vacuum — much like a light bulb. Lilliputian expects to market the SOFC in 2009.
The Direct Methanol Fuel Cell type is an offshoot of the PEMFCs discussed herein. MTI Micro Fuel Cells of Albany, NY, has produced and demonstrated prototypes of its DMFC, mainly for use as battery replacements for electronic cameras and camcorders. Like Lilliputian, MFI expects their fuel-cell to reach the marketplace in 2009.
Toshiba has touted its DMFC fuel-cell technology for several years and has shown it at various technology showcases during that time. It showed a new cell-phone at CEATEC just this fall that uses a small DMFC to charge the lithium-ion battery that goes with the telephone. It has commenced mass production of the DMFC technology.
Panasonic (which recently officially changed its name from Matsushita) is producing a PEMFC for home use, with an output of 120Vac and a power capability of 1kW.
Panasonic has tested these units in Japanese households since 2005, and expects production in 2010. Some of its more interesting specifications: lifetime is 40,000 hours with 4,000 startup cycles (good enough for 10 years of service). It holds up to 200 liters of fuel (assuming you can find it) and it weighs 275 pounds — so don't get too excited about buying one for use at remote broadcasts. Not yet anyway.
For the last three or four years, the introduction of the mass-production of small fuel-cells has been “right around the corner” so the current claims of all parties that 2009 is their target year need to be taken with the proverbial grain of salt. With the energy crisis of 2008, and the strong desire for more green technology from more and more consumers, and the ever-present desire to be freed from the tyranny of rechargeable batteries, it's only a matter of time before small fuel-cells reach the market for real.
Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at firstname.lastname@example.org.
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