The hydrogen rainbow

Hydrogen power is an exciting technology that is likely to be vital for us to achieve a low-carbon or net-zero society. Hydrogen energy is stored in fuel cells, providing us with a clean source of power which is already being used in some vehicles. The production of hydrogen itself, however, can be done using energy from different sources – including fossil fuels – so it’s not always as ’green’ as it could be. This has given rise to a system of colour coding which tells us how the hydrogen was created.

Hydrogen is the lightest and most abundant chemical element in our universe. In fact, it’s thought to make up about 75% of the mass of the universe. As it is such a common element, you might wonder why we would need to produce it synthetically.

Hydrogen may be very common in the make up of living things, but it is rare to find as a gas. Because it only becomes solid at -259°C it’s not unfeasible for us to work with it as solid, but at room temperatures and pressures hydrogen is a combustible gas, which we can burn to produce energy.

We need to synthesise enough hydrogen at an affordable rate to make it an economically viable process. There are different methods of generating hydrogen gas, and it is these differences that the energy sector have used in their colour classification.

Blue
While black, brown, and grey hydrogen production is common in many industries, many employ carbon capture and storage technology to prevent the release of the greenhouse gas by-products into the atmosphere. For production where these techniques are applied, the classification of hydrogen is changed to blue.

Green
Green hydrogen is what the name suggests: a hydrogen production method that doesn’t lead to greenhouse gas emissions. This is completed using a process called electrolysis. Electricity is used to split water into its component elements, hydrogen and water. This type of production is classified green when the electricity used comes from renewable sources, such as wind power, and no greenhouse gas by-products are released.

Black and brown, and grey
Black and brown hydrogen production uses coal or lignite (brown coal formed from peat) in a method called gasification. This is where organic materials are converted at high temperatures into carbon monoxide, carbon dioxide, and hydrogen. Grey hydrogen is one of the most common forms of production through the process of steam reformation. Natural gas, which is mostly made up of methane, is combined with water as steam. It produces hydrogen, but it too produces carbon dioxide as a by-product.

Carbon dioxide is a greenhouse gas, so these drab colours represent hydrogen production that is the most damaging to the environment.

Pink and…turquoise?
Hydrogen production, especially green hydrogen, and its uses as a source of energy is still a developing area, with lots of research ongoing into improving its production, storage, and use. One exciting new step is the co-generation of hydrogen by nuclear energy, known as pink hydrogen. It is hoped that very high-temperature nuclear reactors can be used to generate hydrogen as a secondary process, for example by using the steam for efficient electrolysis. Another low-carbon hydrogen production method still in development is turquoise hydrogen. This involves methane pyrolysis – using electricity to split methane into its components to produce hydrogen and solid carbon, thereby avoiding the release of carbon dioxide.