N°30 I quarterly I july 2013 Focus | 25 w Hydrogen has considerable advantages that could make it a significant source of energy in the future. With three times the energy potential of petroleum, this gas can be used in a fuel cell to produce totally clean electricity: the only by-product of the reaction is water vapor. But it also has a considerable drawback: because it is the lightest of all gases, hydrogen is very difficult to store, especially in on-board systems like those found in cars. To fill a vehicle with four kilos of hydrogen—enough to travel 400 kilometers—its tank would have to hold 45,000 liters of the gas stored at atmo- FUEL CELL. A system in which electricity is produced by the combination of a combustible gas and oxygen. The reaction emits only heat and water. 17 Operating principle of a fuel cell: electricity is produced from hydrogen and oxygen, with water vapor as the only by-product. 18 This robot can manufacture a tank for composite hydrogen, capable of resisting an internal pressure of 700 bars as well as external stress (falling, shearing, chemical products, fire, etc.). spheric pressure. To shrink this volume, hydrogen needs to be compressed, as in most hydrogen-powered electric vehicles. The method is the same as that used to store other energy-producing gases like methane, except that hydrogen requires much higher levels of pressure (about 700 bars) and the compression process itself consumes large amounts of energy. Research is now underway to perfect an alternative storage method: storing hydrogen in solid form. With this system, the gas is chemically bonded to a solid material. “It makes it possible to store as much hydrogen in a given volume as would be by compression, but at more 18 17 © CEA Platef orme Al hyance Inn ovati on, Le Rip ault , 37 © CEA/C. Beurte y A Tankful of H ydrogen
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