- The hydrogen fuel cell car is what most people mean by "hydrogen car." Fuel cells are like batteries in that they are electrochemical devices. They combine substances and use the reaction to generate electricity, but they differ from batteries in that the reactant substances are consumed in the process. In a hydrogen fuel cell, hydrogen is combined with oxygen, using platinum as a catalyst and creating electricity. The sole waste product is water. Most fuel cell designs require the active water be in a vaporous state and therefore function poorly in freezing weather.
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Hydrogen fueling nozzle.Before the 1990s, when people talked about hydrogen-driven automobiles, they meant the Hydrogen Internal Combustion Engines (HICEV). This engine works by substituting hydrogen for gasoline in what's an otherwise conventional car. This is actually a very old idea, as the first internal combustion engine, developed at the beginning of the 19th century, was a hydrogen burner. These engines are so similar to their conventional, gasoline-powered counterparts that kits exist for converting most any car to hydrogen. However, when burned with regular air, hydrogen is not as clean and creates nitrous oxides as waste. Emitted into the atmosphere, these can combine with organic compounds to become a dense, nasty smog. - The third way hydrogen is used to power a car is in the niche field of the rocket car. The normal way to build a hydrogen rocket is to inject very pure hydrogen peroxide onto a silver plate. The silver serves as the catalyst. It causes the extra oxygen atom in the hydrogen peroxide to split off, creating water as a waste product (as in the fuel cell), as well as an enormous amount of heat energy. That heat boils the water into steam, resulting in a powerful jet of steam that provides thrust.
