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Hydrogen
Hydrogen is the most abundant gas in the universe and the simpliest element. Hydrogen, however, is not found freely in nature. It is combined with other elements, like oxygen to create water or carbon to make up the many forms of fossil fuels or hydro-carbons, like natural gas, oil and coal. In fact as we move to "cleaner" fuels, with less carbon, from coal to oil to natural gas, we also move to fuels with a greater percentage of hydrogen. Hydrogen represents the final step in the de-carbonization of energy.
Hydrogen must be isolated in order to put it to use, for this reason hydrogen can be thought of as an energy carrier, similar to electricity, rather than an energy source. Hydrogen has some advantages over electricity because it can be more easily stored and can be used both directly as a fuel through combustion or to produce electricity in a fuel cell.
Hydrogen is most often produced through steam reformation of natural gas, which releases carbon dioxide. It can also be produced from the electrolysis of water using electricity from any source of electricity- including renewables. It can also be extracted from sewage gas, naptha or biogas.1 Research is currently underway to produce renewable hydrogen directly from sunlight as well as from microbes.
Production
Hydrogen is currently predominantly produced via the catalytic steam reforming of methane to give hydrogen and carbon dioxide. However, natural gas is not a renewable source of fuel and ultimately contributes to the worldwide increase in global emissions of carbon dioxide.
Perhaps the most promising method of producing hydrogen is simply by the electrolytic splitting of water (electrolysis), in which an electric current is passed through water, decomposing it into hydrogen at the negatively charged cathode and oxygen at the positive anode. If the electricity used to split the water is generated from a renewable source such as solar, wind, biomass, wave, tidal, geothermal or hydropower then there is the potential to produce hydrogen sustainably in a non-polluting manner.
Photoelectrochemical (PEC) production uses semiconductor technology in a one-step process that utilises the energy from sunlight to produce an electric current which electrolyses water in a single device. Other methods of renewable hydrogen production include the high temperature gasification and low-temperature pyrloysis of biomass (agricultural waste, wood, domestic organic waste). In pyrolysis, biomass is broken down into highly reactive vapours and a carbonaceous residue, or char. The vapours can then be steam reformed to produce hydrogen.
There is also considerable interest in the photobiological production of hydrogen by microbes.2
Applications
Hydrogen gas is the primary fuel for fuel cells to produce electricity for industrial, transport and domestic use. It has been the fuel used to provide electricity for the space shuttle for the last two decades via on-board fuel cells that combine hydrogen and oxygen to generate electricity; the exhaust from the fuel cell – pure water – is used by the crew as drinking water.3
Hydrogen can also be combusted as a fuel to drive a vehicle and to heat water.
Hydrogen can also be combusted for use in a gas turbine to replace natural gas.
Footnotes
1http://www.tn.gov.in/spc/tenthplan/CH_11_2.PDF
Resources
International Partnership for a Hydrogen Economy was established in 2003 to accelerate the transition to a hydrogen economy. The IPHE undertakes coordinated research, development and deployment. The resources page on this site has a large amount of basic educational material as well as more technical reports.
International Energy Agency Hydrogen Implementing Agreement The IEA HIA pursues collaborative research and development and information exchange among member countries. This site offers links to a number of national hydrogen programs, case studies, and technical reports.
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