Electrical applications of carbon fiber –fuel cells

Fuel cells have become a most promising new technology for providing energy and a rapid growth in usage in predicted. A fuel cell is an electrochemical energy device that converts hydrogen fuel, in the presence of O2 from the air, into electrical energy, heat and water. The attributes of fuel cells are zero emissions of particulates, CO2, CO, NOx, as well as being virtually noiseless.

Hydrogen is the primary fuel source for a fuel cell and can be used directly or derived from a hydrocarbon fuel such as natural gas, mechanol and hydrocarbon fuels through the process of reforming. The reforming process converts the fuel source to H2 using steam:

CH4 + H2O →/←CO + 3H2

And can be undertaken external to the cell, or internally, where the products introduced into the cell are electrochemically oxidized. Hydrogen can also be derived from organic matter of plant and animal origin.

The purity of H2 supplied to a given fuel cell system will depend on that particular fuel cell technology. Each cell is limited to about 1.23 V, so to achieve the necessary power requirement, a number of cells are stacked and a collection of these fuel cell stacks can be used to produce a power plant. The conversion of the chemical energy of a fuel into electrical energy without combustion is quite efficient and remarkably clean.

In the search for a fuel cell for a new generation of vehicles, there has been a concerted effort for the development of partnerships, with vehicle manufacturers working closely with government departments and research organizations to overcome technical barriers with innovative approaches to produce fuel cells suitable for use in concept vehicles, such as the Daimler Chrysler Jeep commander, Ford P2000 and the GM precept. Simutaneously, there have been improvements in the clean-up of emissions like CO and S, which are also pertiment for running the fuel cells more efficiently. In an automobile, H2 can be stored as a metal hydride, or as a cryogenic liquid and finally, as a compressed gas. Since there is no established distribution system for H2, fuel cell cars will initially use a catalytic reformer to generate H2 from a liquid fuel such as methanol.

If a reformate is used, catalytic converters can remove emissions which cause smog, but CO2 cannot be readily removed from on board the vehicles.

Carbon fibers have featured in several aspects of this work, but due to its proprietary nature, only brief details are available. Certainly, by looking at the recent patent literature, the field of using carbon fiber for fuel cells is very active- The university of California have used treated carbon fibers to improve performance; Hyperion catalysts have used carbon fibrils for Li battery electrodes; Sandia corp describe a method of preparing carbon materials for use as electrodes in rechargeable batteries; Mitsubishi Chemical detail an electrode material for a non-aqueous solvent secondary battery; Mitsubish Gas chemical describe a method of producing isotropic pitch carbon fibers and carbon materials for non-aqueous solvent secondary battery; and Petoca describe the use of mesophase pitch based carbon fiber for use as the negative electrode of a secondary batter.

There are basically five types of fuel cells, which are characterized by the type of electrolyte used.

 

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