Learn more about electrolysis. Direct solar water splitting, or photolytic, processes use light energy to split water into hydrogen and oxygen. These processes are currently in various early stages of research but offer long-term potential for sustainable hydrogen production with low environmental impact.
Learn more about the following solar water splitting processes:. Microbes such as bacteria and microalgae can produce hydrogen through biological reactions, using sunlight or organic matter. The environmental impact and energy efficiency of hydrogen depends on how it is produced. Several projects are underway to decrease costs associated with hydrogen production. The carbon monoxide is reacted with water to produce additional hydrogen.
This method is the cheapest, most efficient, and most common. Natural gas reforming using steam accounts for the majority of hydrogen produced in the United States annually. A synthesis gas can also be created by reacting coal or biomass with high-temperature steam and oxygen in a pressurized gasifier.
This converts the coal or biomass into gaseous components—a process called gasification. The resulting synthesis gas contains hydrogen and carbon monoxide, which is reacted with steam to separate the hydrogen. Electrolysis : An electric current splits water into hydrogen and oxygen. If the electricity is produced by renewable sources, such as solar or wind, the resulting hydrogen will be considered renewable as well, and has numerous emissions benefits. Power-to-hydrogen projects are taking off, using excess renewable electricity, when available, to make hydrogen through electrolysis.
Renewable Liquid Reforming : Renewable liquid fuels, such as ethanol , are reacted with high-temperature steam to produce hydrogen near the point of end use. Poll and L. Wolniewciz, The quadrupole moment of the H 2 molecule, J.
Prigogine and S. Rice, eds. CrossRef Google Scholar. Bishop and L. Cheung, Static higher polarizabilities of H 2 , Phys. A20, — ADS Google Scholar.
Wolniewicz, Polarizability of the hydrogen molecule, J. Dunham, The energy levels of a rotating vibrator, Phys. Van Kranendonk and G. Karl, Theory of the rotational and vibrational excitations in solid parahydrogen, and frequency analysis of the infrared and Raman spectra, Rev. Baran and W. Kolos, Vibrational constants for the ground state of the hydrogen molecule, J. Stoicheff, High resolution Raman spectroscopy of gases.
Fink, T. Wiggins, and D. Rank, Frequency and intensity measurements of the quadrupole spectrum of molecular hydrogen, J. Foltz, D. Rank and T. Natural gas, essentially composed of methane CH 4 , contains sulfur which must be removed during a hydrodesulfurization step.
Once purified, the methane reacts with steam to form a synthesis gas containing carbon monoxide CO and hydrogen H 2.
Then, the water vapor reacts with the carbon monoxide of the synthesis gas to form carbon dioxide CO 2 and more hydrogen. This blend, rich in CO 2 and H 2 , is then purified to obtain about Separating the components water molecules makes it possible to produce hydrogen. Water molecules H 2 O is composed of two hydrogen atoms H and one oxygen atom O. To produce hydrogen, it is necessary to break the bonds of this molecule.
Different processes exist using an electric current or a succession of chemical reactions. The protons accept electrons in an oxidation reaction thus forming hydrogen gas. The electrolysis itself does not emit any CO 2. But in an overall calculation, the production of electricity must be taken into account.
In the case where the electricity used is produced from sources that do not emit CO 2 renewable energies, etc. This method is generally used to produce low volumes of hydrogen or near low-cost electric power sources hydroelectricity.
Currently, a lot of research is being done to improve the efficiency of electrolysis. One area of improvement is the high-temperature electrolysis of water vapor. This technology can, for example, be coupled with a set of solar mirrors which concentrate the Sun's rays to reach these very high temperatures, which would make it possible to produce hydrogen with virtually no greenhouse gases. The thermochemical cycles involve the phenomenon of decomposition of water into hydrogen and oxygen which takes place spontaneously at a very high temperature.
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