People write and talk about green, grey, blue hydrogen. What is actually meant by this?

Hydrogen is a colorless chemical element. Colours are attributed to hydrogen in order to identify the way it is formed as simply and unambiguously as possible.

• Green hydrogen is produced by electrolysis of water with electricity from renewable sources. This hydrogen is CO2 free
• Grey hydrogen is produced from fossil fuels and in particular by steam reforming of natural gas CO2 is produced during the production process.
• Blue hydrogen is basically grey hydrogen, but the CO2 produced is captured and stored (Carbon Capture and Storage, CCS).
• Turquoise hydrogen is also produced from natural gas. The methane contained in natural gas is split by pyrolysis. A by-product of this process is solid carbon, which can be stored. If the reactor is powered by renewable energy, the hydrogen is CO2 neutral.

Other hydrogen colors: White hydrogen is naturally occurring hydrogen, sometimes used to refer to hydrogen produced as a byproduct in chemistry. Brown hydrogen is produced from the gasification of coal or petroleum (sometimes called black hydrogen). Orange hydrogen is produced from biomass or with electricity from waste-to-energy plants. Purple hydrogen (sometimes called pink, red or yellow hydrogen) is produced by electrolysis of water using nuclear electricity.

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