A fuel cell is an energy conversion device that generates electricity and heat by electrochemically combining a gaseous fuel and an oxidizing gas via an ion conducting electrolyte. The chief characteristic of a fuel cell is its ability to convert chemical energy directly into electrical energy without the need for combustion, giving much higher conversion efficiencies than conventional thermo-mechanical methods (eg steam turbines). Consequently fuel cells have much lower carbon dioxide emissions than fossil fuel-based technologies for the same power output.
Fuel cells can potentially be used to power everything from cars and laptop computers to manufacturing plants. Commercially available fuel cells produce electricity from hydrogen through a non-combustion chemical reaction rather that direct firing. As a result, they are quiet, clean and efficientand produce energy in the form of electricity and heat when fuel is supplied, discharging benign byproducts like water. Residential fuel cells supply between 2-5 kilowatts of power and are mostly in the experimental stage. Meanwhile, those used for commercial enterprises can generate 200-plus kilowatts and are implemented if businesses need uninterruptible power or where access to the transmission grid is limited.
Every major automaker is investing in fuel cells, not to mention the major fuel cell makers: Ballard, FuelCell Energy, Siemens-Westinghouse and International Fuel Cells. In 2003, Dow Chemical Co. and General Motors Corp. partnered to foster the development of fuel cellsa deal which could lead to the buying or leasing of 500 more units by 2010.
The current fuel cell market is slow because of price and technology. Advances in technology could accelerate market acceptance, but the industry is having difficulty getting needed economies of scale because it is fragmented. To help kick start the fuel cell industry, President Bush has called for $1.7 billion over five years to research and develop fuel cells.
A solid oxide fuel cell (SOFC) unit consists of two electrodes (an anode and cathode) separated by the electrolyte (Figure 1). Hydrogen, H2, arrives at the anode, where it reacts with oxygen ions from the electrolyte, thereby releasing electrons (e-) to the external circuit. On the other side of the fuel cell, oxidant (eg O2 or air) is fed to the cathode, where it supplies the oxygen ions (O2-) for the electrolyte by accepting electrons from the external circuit. The electrolyte conducts these ions between the electrodes, maintaining overall electrical charge balance. The flow of electrons in the external circuit provides useful power.
Again, Hydrogen gas (H2) flows into channels on one face of the cell and migrates through that electrode, while the same occurs with oxygen gas (O2, typically from the ambient air) along the opposite electrode. Spurred by a catalyst, favorable chemistry causes the hydrogen to oxidize into hydrogen protons and give up its electrons to the neighboring electrode, which thereby becomes the anode. This buildup of negative charge then follows the path of least resistance via the external circuit to the other electrode (the cathode). It is this flow of electrons through a circuit that creates electricity.
This would not continue for long without a complete electrochemical cycle. As the electrical current begins to flow, hydrogen protons pass through the membrane from the anode to the cathode. When the electrons return from doing worklighting your house, charging a battery, or powering your car's motor, for examplethey react with oxygen and the hydrogen protons at the cathode to form water. Heat emits from this union (an exothermic reaction), as well as from the frictional resistance of ion transfer through the membrane. This thermal energy can be utilized outside the fuel cell.
Several types of fuel cells are now being developed around the world, the chief difference between them being the material used for the electrolyte (and thus also their operating temperature). Small, alkaline fuel cells (utilizing a liquid electrolyte) were developed by NASA and improved versions are still used on the Space Shuttle today. Solid oxide fuel cells (SOFCs), in contrast, are constructed entirely from solid-state materials; they utilize a fast oxygen ion conducting ceramic as the electrolyte, and operate in the temperature range 900-1000oC.
While nearly all fuel cells are currently utilizing natural gas as their fuel source, other companies are looking for alternatives. A California-based company, Scientific Applications & Research Associates, Inc. (SARA), has successfully tested a fuel cell that runs on carbon, which is derived from one of the Unites States' most abundant natural resources, coal. To progress the technology, SARA and American Electric Power (AEP) have formed a Joint Industry Program (JIP) to enable the scale-up of the Direct Carbon Fuel Cell to commercial viability.
The markets that are driving the demand for all types of fuel cells and particularly stationary ones are in Asia where electricity prices run high. Hoku Scientific, for example, plans to introduce its first innovation to Asia in 2005. Hoku is developing a high-efficiency fuel cell that will generate electricity and hot water for the family home. Vancouver, Canada-based Ballard Power Systems recently launched a pre-commercial one-kilowatt combined heat and power fuel cell generator to be used in the residential market in Japan.
Hydrogen is produced mainly from natural gas using steam reformationa method that does nothing to limit the reliance on fossil fuels or the infrastructure that must carry them. Running electricity through water (electrolysis) can also create hydrogen. Unfortunately, the amount of energy used to make hydrogen is more than the amount of power produced by fuel cells and pollutes when fossil fuels are used. Renewable sources could create the electricity to produce hydrogen but is not reliable or cost effective. Nuclear power is the best way to generate the hydrogen needed to power fuel cells.
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