Catalysts
A catalyst is defined as a substance, usually used in small amount relative to the reactions, that modifies and increases the rate of a reaction without being consumed in the processes. Fuel cells which run at low temperatures require efficient catalysts.
The majority of catalysts are made primarily of platinum (Pt). Due to the rarity of this metal, scientists are experimentating with doping Pt with such metals as palladium (Pd) or ruthenium (Ru) and complexes of cobalt and nitrogen to help reduce the cost of producing a purely platinum catalyst. It has been estimated that if PEM fuel cells (See Fuel Cell Types) replaced the internal combustion engine, there wouldn’t be enough platinum in the world to cover demands for catalyst production. Additionally, the United States produces very little platinum. Most of the world's platinum comes from the former Soviet Union and other politically unstable areas.
The Pt catalyst, or alloys containing it, is deposited in a thin sheet on top of each electrode. Research is currently focused on reducing the amount of platinum needed in each fuel cell by increasing the utilization efficiency. A new deposition technique for these catalytic electrode metals is diagrammed below. With this technique, a chamber containing the electrode is pressurized with argon, a high voltage is applied and the catalyst is deposited in layers only a few atoms thick. Techniques such as sputtering (pictured below) help decrease the amount of catalyst used, reducing production prices and increasing the feasibility of the fuel cell.
In addition to the scarcity of Pt on earth, repeated replacement of the Pt catalyst may be needed due to the purity of the fuel source used. It has been shown that a hydrogen fuel source containing as little as 10-20 ppm of CO could poison the catalyst. This poisoning results from the CO binding with the Pt, rendering it useless as a catalyst. Thus, the future technology of better refinement of hydrogen fuel could increase the life of Pt within the fuel cell.
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