The colors of hydrogen: what do they mean?

Hydrogen itself is colorless. It is a gas that can be stored in liquid form under pressure. So why all the color codes? They are intended to indicate the production method and, by extension, the level of sustainability. So, what do the different colors of hydrogen mean?

Grey hydrogen

When hydrogen is produced from fossil fuels—such as coal, natural gas, and petroleum—we refer to it as gray hydrogen. This process releases approximately nine tons of CO2 into the atmosphere for every ton of hydrogen produced. Currently, about 95% of the world’s hydrogen is produced in this way. Often using natural gas via large reformers (steam methane reforming – SMR).

Blue hydrogen

When producing gray hydrogen, we can capture and store most of the CO2. We call this carbon capture and storage (CCS). The CO2 can also be used as a feedstock; in that case, we refer to it as carbon capture and utilization (CCU). We then refer to it as blue or “low-carbon hydrogen.” Residual hydrogen from industry—such as from chlorine production—is also referred to as blue hydrogen.

Gray and blue hydrogen therefore still have a fossil fuel origin.

Green hydrogen

Hydrogen is called “green” when it is produced using electricity. This is done through electrolysis. Electrolysis is the process of using an electric current to split water molecules into oxygen and hydrogen gas by placing electrodes in an electrolyte solution. When this is done using green electricity, green hydrogen is produced.

Pink hydrogen

Pink hydrogen is produced from water and electricity generated by nuclear power plants. Since this process does not release any CO2, it is considered green. However, the specific characteristics of nuclear energy—such as nuclear waste—are, of course, linked to the hydrogen produced.