The colours of the hydrogen rainbow

 Green hydrogen – Made by using clean electricity from renewable energy technologies to electrolyse water (H2O), separating the hydrogen atom within it from its molecular twin oxygen. At present, very expensive.

• Blue hydrogen – Produced using natural gas but with carbon emissions being captured and stored, or reused. But negligible amounts are being produced due to a lack of carbon-capture projects.
• Grey hydrogen – This is the most common form of hydrogen production: it comes from natural gas via steam methane reformation but without emissions capture.
• Brown hydrogen – The cheapest way to make hydrogen but also the most environmentally damaging due to the use of thermal coal in the production process.
• Turquoise hydrogen – Uses a process called methane pyrolysis to produce hydrogen and solid carbon. But it is not proven at scale, and there are concerns around methane leakage.