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  • Methods of hydrogen storage for subsequent use span many approaches,

  • including high pressures, cryogenics, and chemical compounds that reversibly

  • release H2 upon heating. Underground hydrogen storage is useful to provide

  • grid energy storage for intermittent energy sources, like wind power, as well

  • as providing fuel for transportation, particularly for ships and airplanes.

  • Most research into hydrogen storage is focused on storing hydrogen as a

  • lightweight, compact energy carrier for mobile applications.

  • Liquid hydrogen or slush hydrogen may be used, as in the Space Shuttle. However

  • liquid hydrogen requires cryogenic storage and boils around 20.268 K.

  • Hence, its liquefaction imposes a large energy loss. The tanks must also be well

  • insulated to prevent boil off but adding insulation increases cost. Liquid

  • hydrogen has less energy density by volume than hydrocarbon fuels such as

  • gasoline by approximately a factor of four. This highlights the density

  • problem for pure hydrogen: there is actually about 64% more hydrogen in a

  • liter of gasoline than there is in a liter of pure liquid hydrogen. The

  • carbon in the gasoline also contributes to the energy of combustion.

  • Compressed hydrogen, by comparison, is stored quite differently. Hydrogen gas

  • has good energy density by weight, but poor energy density by volume versus

  • hydrocarbons, hence it requires a larger tank to store. A large hydrogen tank

  • will be heavier than the small hydrocarbon tank used to store the same

  • amount of energy, all other factors remaining equal. Increasing gas pressure

  • would improve the energy density by volume, making for smaller, but not

  • lighter container tanks. Compressed hydrogen costs 2.1% of the energy

  • content to power the compressor. Higher compression without energy recovery will

  • mean more energy lost to the compression step. Compressed hydrogen storage can

  • exhibit very low permeation. Automotive Onboard hydrogen storage

  • Targets were set by the FreedomCAR Partnership in January 2002 between the

  • United States Council for Automotive Research and U.S. DOE. The 2005 targets

  • were not reached in 2005. The targets were revised in 2009 to reflect new data

  • on system efficiencies obtained from fleets of test cars. The ultimate goal

  • for volumetric storage is still above the theoretical density of liquid

  • hydrogen. It is important to note that these

  • targets are for the hydrogen storage system, not the hydrogen storage

  • material. System densities are often around half those of the working

  • material, thus while a material may store 6 wt% H2, a working system using

  • that material may only achieve 3 wt% when the weight of tanks, temperature

  • and pressure control equipment, etc., is considered.

  • In 2010, only two storage technologies were identified as being susceptible to

  • meet DOE targets: MOF-177 exceeds 2010 target for volumetric capacity, while

  • cryo-compressed H2 exceeds more restrictive 2015 targets for both

  • gravimetric and volumetric capacity. = Established technologies =

  • Compressed hydrogen Compressed hydrogen is the gaseous state

  • of the element hydrogen which is kept under pressure. Compressed hydrogen in

  • hydrogen tanks at 350 bar and 700 bar is used for hydrogen tank systems in

  • vehicles, based on type IV carbon-composite technology. Car

  • manufacturers have been developing this solution, such as Honda or Nissan.

  • Liquid hydrogen BMW has been working on liquid tank for

  • cars, producing for example the BMW Hydrogen 7.

  • = Proposals and research = Hydrogen storage technologies can be

  • divided into physical storage, where hydrogen molecules are stored, and

  • chemical storage, where hydrides are stored.

  • Chemical storage Chemical storage could offer high

  • storage performance due to the strong interaction. However, the regeneration

  • of storage material is still an issue. A large number of chemical storage systems

  • are under investigation, which involve hydrolysis reactions,

  • hydrogenation/dehydrogenation reactions, ammonia borane and other boron hydrides,

  • ammonia, and alane etc. = Metal hydrides =

  • Metal hydrides, such as MgH2, NaAlH4, LiAlH4, LiH, LaNi5H6, TiFeH2 and

  • palladium hydride, with varying degrees of efficiency, can be used as a storage

  • medium for hydrogen, often reversibly. Some are easy-to-fuel liquids at ambient

  • temperature and pressure, others are solids which could be turned into

  • pellets. These materials have good energy density by volume, although their

  • energy density by weight is often worse than the leading hydrocarbon fuels.

  • Most metal hydrides bind with hydrogen very strongly. As a result, high

  • temperatures around 120 °C – 200 °C are required to release their hydrogen

  • content. This energy cost can be reduced by using alloys which consists of a

  • strong hydride former and a weak one such as in LiNH2, LiBH4 and NaBH4. These

  • are able to form weaker bonds, thereby requiring less input to release stored

  • hydrogen. However, if the interaction is too weak, the pressure needed for

  • rehydriding is high, thereby eliminating any energy savings. The target for

  • onboard hydrogen fuel systems is roughly

Methods of hydrogen storage for subsequent use span many approaches,

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B2 hydrogen storage energy density compressed liquid

Hydrogen storage

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    songwen8778 posted on 2016/07/22
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