What is the difference between grey, blue and green hydrogen?

Hydrogen has no colour. The colour of the hydrogen refers to its production process.

• Grey hydrogen refers to the origin of natural gas which is typically cracked in a steam methane reformer. During this reforming process, CO₂ is produced as a side product.
• Blue hydrogen is produced in the same way as grey hydrogen (using natural gas), but here the CO₂ produced is stored underground instead of in the air.
• If the hydrogen is produced by green electricity through an electrolysis process, the hydrogen is referred to as ‘green’.