There is a whole range of hydrogen “colors.” The color indicates the production method and carbon footprint of the hydrogen; however, there is no uniform international or industry-wide definition for these colors. Some hydrogen colors have the same meaning, while some meanings are assigned to multiple colors. Here is an overview of the common colors and their meanings.
Generally speaking, hydrogen colors are divided into three categories:
- Fossil
- Low-carbon
- Renewable
Fossil Hydrogen
Gray hydrogen isproduced from fossil fuels. Often, no distinction is made between different types of fossil fuels. Essentially, the term “gray” hydrogen means that it was produced from fossil hydrocarbons such as natural gas. This is done either “traditionally” through steam reformingor through electrolysis using electricity generated from fossil fuels.
In steam reforming, methane reacts with highly heated steam toform carbon monoxide and oxygen. In a second step, known as the water-gas shift reaction, the carbon monoxide reacts again with steam,producing more hydrogen andCO2 . This CO2 escapes unused into the atmosphere. Producing one metric ton of hydrogen in this way generates about 10 metric tonsof CO2. Today, about 90% of the hydrogen produced in Germany still comes from fossil sources. Of this, about 40% is produced via steam reforming, and another approximately 50% is produced as a byproduct of refining and chemical processes.
Upon closer examination, fossil hydrogen is further classified as follows:
Black hydrogen isproduced through the gasification of bituminous coal.
Brown hydrogen isproduced through the gasification of lignite.
Hydrogen is either golden or white when it is extracted from natural deposits. These deposits can form in various ways:
- through the bacterial breakdown of organic material
- through the transformation of water during the decay of radioactive elements in the Earth's crust
- through serpentinization—a process in which mantle rock reacts with water, forming new minerals and hydrogen
Natural hydrogen reservoirs have hardly been studied to date, which is why only a few deposits are known. In theory, naturally occurring hydrogen could be extracted using fracking technologies. However, extraction methods still need to be studied further.
Low-carbon hydrogen
Hydrogen is classified as “yellow” when grid electricity—typically a mix of renewable and fossil fuels—is used to power the electrolysers. Sometimes the term “yellow hydrogen” is also used to refer to hydrogen produced using nuclear power.
The term "blue hydrogen" refers to hydrogenproduced in a process where theCO2 generated is separated, captured, and stored so that it does not enter the atmosphere. Because of this storage (CCS = Carbon Capture and Storage), the production is consideredcarbon-neutral on a net basis.
Turquoise hydrogen is produced through the thermal cracking of methane, a process known as methane pyrolysis. In this process, methane is broken down into its components—hydrogen and carbon—in the absence of oxygen. As a result, solid carbon is produced instead ofCO2. The process isCO2-neutral if the high-temperature reactor is heated using renewable energy sources and the carbon is permanently sequestered. Alternatively, the solid carbon can be used as a raw material in the chemical industry, among other applications.
Pink, red, or violet hydrogenis produced when nuclear power is used to power the electrolysis process.
Renewable Hydrogen
Green hydrogenis produced through the electrolysis of water. In this process, water is broken down into its components: hydrogen and oxygen. However, the hydrogen is considered "green" only if the electricity used comes exclusively from renewable energy sources. Production is thereforeCO2-free. Hydrogen produced through the gasification and fermentation of biomass, as well as through the steam reforming of biogas, is sometimes also considered green hydrogen.
Hydrogen isreferred to as “orange”when bioenergy is used in its production. This hydrogen is therefore produced from organic materials such as biomass, biofuel, biogas, and biomethane. The organic materials are typically derived from waste and residues from agriculture and forestry, as well as from households and industry. This is carbon-neutral energy. In some cases, however, “orange hydrogen” also refers to hydrogen produced through the pyrolysis of waste.
About the Brief Study on “Hydrogen—The Theory of Colors”
