About Hydrogen Car Technology
The hydrogen car is a family of alternative automotive technologies. The best-known branch is the hydrogen fuel cell, which showed a lot of promise in the 1990s but has since been largely supplanted by the hybrid electric car. Using hydrogen as a replacement for petroleum-based fuels has roots dating back two centuries. High-speed rocket cars have used hydrogen as a fuel source for decades; high-test hydrogen peroxide is one of the earliest forms of rocket fuel.
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Hydrogen Internal Combustion Engines
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Before the 1990s, talk of hydrogen-driven automobiles usually referred to the hydrogen internal combustion engine (HICEV). This was actually the modernization of an old idea, as the first internal combustion engine ever developed used hydrogen fuel. The technology works by substituting hydrogen for gasoline or diesel, and excluding a few changes to accommodate this, HICEVs are essentially conventional cars. They're so similar to their normal counterparts that kits exist for converting most any car to hydrogen fuel. However, when hydrogen is burned, it creates nitrous oxides as exhaust. Emitted into the open atmosphere, these can combine with organic compounds to become a dense, nasty smog.
Hydrogen Fuel Cells
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The term "hydrogen car" means a hydrogen fuel cell vehicle. Fuel cells are similar to batteries; both are electrochemical devices. They combine substances and use the reaction to generate electricity, but fuel cells differ from batteries in that the reactant substances come into actual contact and are consumed in the process. In hydrogen fuel cells, hydrogen is combined with oxygen, using platinum as a catalyst. The reaction creates electricity and water. The electricity is then used to drive an electric motor to provide the car's motive power.
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Hydrogen Fuel Cell Deficiencies
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Hydrogen fuel cells are beset with problems that have prevented them from becoming an economical substitute for petroleum-fired engines. They're usually too fragile for use on consumer and commercial vehicles. Most fuel cell designs require that the active water be in a vaporous state, so they function poorly in freezing weather. Finally, so long as platinum is used as the main catalyst for the fuel cell's reaction, the cells will be very expensive.
Hydrogen Fuel Economics
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The other limitation on hydrogen fuel cells is the hydrogen itself. Hydrogen is a very common element on Earth, bound up into a variety of substances that are easily accessed. There are also many means for extracting hydrogen out of whatever it's bound up in, such as water. However, all of those processes share one trait: They all require more energy to make than the yielded hydrogen could provide to a car. Whether it be in terms of petrol fuels or straight electricity, sending the energy directly to the car and not to hydrogen processing is always more efficient.
Rocket Cars
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The third and final way hydrogen is used to run car is in the specialized world of the rocket car. Ultrapure hydrogen peroxide, called "high test," is one of the oldest forms of rocket fuel. This hydrogen peroxide is dozens of times more concentrated than the stuff available on a pharmacy shelf. The high-test peroxide is injected onto a silver plate. The silver serves as the catalyst for the reaction, causing the extra oxygen atom in the hydrogen peroxide to split away. This creates water (as in the fuel cell reaction) and an enormous amount of heat. That heat boils the water into steam, resulting in a powerful jet of steam that provides the rocket engine's thrust.
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