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Most hydrogen is produced from fossil fuels, resulting in carbon dioxide emissions. [169] Hydrogen produced by this technology has been described as grey hydrogen when emissions are released to the atmosphere, and blue hydrogen when emissions are captured through carbon capture and storage (CCS).
Hydrogen can be produced from many different sources in different ways to use as a fuel. The two most common methods for producing hydrogen are steam-methane reforming and electrolysis (splitting water with electricity). Researchers are exploring other hydrogen production methods, or pathways.
Hydrogen can be produced using a number of different processes. Thermochemical processes use heat and chemical reactions to release hydrogen from organic materials, such as fossil fuels and biomass, or from materials like water.
Using a renewable source, hydrogen could be produced by electrolysis, biohydrogen, thermochemical cycles, photocatalysis, and plasmolysis. Amongst hydrogen production technologies, electrolysis contributes the highest 4% of the total world’s energy demand.
Hydrogen use today is dominated by industry, namely: oil refining, ammonia production, methanol production and steel production. Virtually all of this hydrogen is supplied using fossil fuels, so there is significant potential for emissions reductions from clean hydrogen.
Hydrogen can be produced from diverse, domestic resources, including fossil fuels, biomass, and water electrolysis with electricity. The environmental impact and energy efficiency of hydrogen depends on how it is produced.
Electrolysis is a promising option for carbon-free hydrogen production from renewable and nuclear resources. Electrolysis is the process of using electricity to split water into hydrogen and oxygen. This reaction takes place in a unit called an electrolyzer.
There are several ways to use hydrogen for energy once it is produced. The most prominent is in fuel cells, which convert the chemical energy stored in hydrogen and oxygen into electricity. Unlike with gasoline-fueled engines, there are no harmful emissions like carbon dioxide.
The most important industrial method for the production of hydrogen is the catalytic steam–hydrocarbon process, in which gaseous or vaporized hydrocarbons are treated with steam at high pressure over a nickel catalyst at 650°–950° C to produce carbon oxides and hydrogen: C n H 2n+2 + n H 2 O → n CO + (2 n + 1)H 2; C n H 2n+2 + 2 n H 2 O→ n CO 2 ...
Hydrogen production is technically and economically feasible from biomass and residual wastes, given the existing technology and economic conditions in many developed countries. It has been stated that biomass will cover the energy demand by more than 25% by 2050.