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Hydrogen economy and storage

by Richard Lee 2011

Even though the first internal combustion engine burning hydrogen fuel was invented way back in 1807, the use of the term hydrogen economy, as a system of delivering energy, was not coined until 1970, in a talk given by John Bockris, at the General Motors (GM) Technical Center.

This hydrogen economy promotes hydrogen as a fuel for transportation, for the energy needs of buildings and industry; and for portable electronic devices. The current interest is understandable since the waste product from hydrogen combustion is simply water. However free hydrogen does not occur naturally in the atmosphere in any quantity, and must be produced from other energy sources. Hydrogen is therefore an energy carrier like electricity, and not a primary energy source, such as petroleum. The benefits of a hydrogen economy therefore depends on issues of energy sourcing, including fossil fuel use, climate change, and renewable energy generation.

Hydrogen energy applications can span a wide power range: from small scale use in fuel cells which could power your mobile phone; to hydrogen powered vehicles; and to large scale applications in electricity generation and storage.

The power plants of hydrogen vehicles convert the chemical energy of hydrogen to mechanical energy either by burning hydrogen in an internal combustion engine, or by reacting hydrogen with oxygen in a fuel cell to produce electricity to run electric motors. However, there are much higher purity requirements (99.99% or better) for fuel cell applications. Widespread use of high purity hydrogen for fuelling transportation is a key element of a proposed hydrogen economy.

With these mobile applications, fuel storage becomes one of the major challenges. The current technology includes the storage of liquefied or pressurised gas. Liquefaction requires large amounts of energy and also maintaining cryogenic temperatures using thermal insulation. Pressurised hydrogen gas has good energy density by weight, but poor energy density by volume versus hydrocarbons, hence it requires a large tank size. A large hydrogen tank will be heavier than the small hydrocarbon tank used to store the same amount of energy. Also tanks of hydrogen, especially in vehicle applications have inherent safety issues.

Hydrogen can also be stored as a chemical hydride phase where the hydrogen reacts to form the hydride and then decomposed when required, to provide the gas phase. Another well researched approach uses porous metal alloys as a solid-state storage method working as a sort of “hydrogen sponge”. This solid state storage may potentially use carbon nanotubes as storage media. The widespread use of hydrogen in vehicles will therefore need a widespread distribution network including hydrogen filling stations.

Remember that hydrogen is just the energy carrier and that a primary source of energy is needed. This can be from a renewable source such as biomass gasification or can be from fossil fuel sources (natural gas or coal) using the chemical reactions of steam reforming and water gas shift. Other methods can use electricity for water electrolysis. This electricity can again be from a (non-renewable) power station source or from a renewable photovoltaic solar cell system.

Also high temperature processes are possible (electrolysis and catalysis) using sources of high temperature heat. These can include nuclear fission reactors; concentrating solar mirror collectors; and geothermal sources.  There are also biotechnology approaches to generating hydrogen such as fermentation processes using bacteria, microbes and enzymes which can work on waste materials.

Hydrogen therefore only becomes a renewable low carbon fuel if it is generated from a renewable primary energy source. However it is still possible to produce a true clean source of hydrogen from fossil fuels if some form of carbon capture or carbon sequestration is performed during the hydrogen production process.

Major relevant Inspec thesaurus terms:

alkaline fuel cells
bioenergy conversion
biofuel
biotechnology
catalysis
combustion
direct alcohol fuel cells
direct carbon fuel cells
direct ethanol fuel cells
direct methanol fuel cells
electrolysis
fermentation
fuel cell power plants
fuel cell vehicles
fuel cells
fuel gasification
fuel processing
fuel processing industries
hydrogen
hydrogenation
hydrogen economy
hydrogen production
hydrogen storage
microbial fuel cells
molten carbonate fuel cells
phosphoric acid fuel cells
proton exchange membrane fuel cells
solid oxide fuel cells
steam reforming
syngas
water gas shift

Important classification codes:

 

A8610B Fossil and other fuels
A8630G Fuel cells
A8640K Hydrogen storage and technology
B8210 Energy resources
B8255 Fuel cell power plants
B8410G Fuel cells
B8470 Other energy storage
B8520 Transportation
E1525 Industrial processes
E3624 Fuel processing industry
E3628Biotechnology Industry