Opinion: Decoding the Hydrogen T-Rainbow

Opinion: Decoding the Hydrogen T-Rainbow
05 November 2021

Hydrogen colour codes cracked

There is much written about hydrogen in the press and media, but if like the author, you are just starting out along your hydrogen journey and you are perhaps suffering colour confusion, then this little blog guide to deciphering the colours of hydrogen will hopefully brighten your day.

Whilst Hydrogen itself is a colourless gas, a colour name is often attributed to it to denote how that hydrogen is produced. Hydrogen occurs naturally in nature, but it is quite rare and is sometimes known as white hydrogen.  On an industrial scale hydrogen is generated using another fuel/process and this gives the hydrogen its colour name.

A T-rainbow of hydrogen colour

  Colour Fuel Process Products

Brown/Black Coal Steam reforming or gasification H2 + CO2 (released)

White N/A Naturally occurring H2

Grey Natural Gas Steam reforming H2 + CO2 (released)

Blue Natural Gas Steam reforming H2 + CO2 (% captured and stored)

Turquoise Natural Gas Pyrolysis H2 + C (solid)

Red Nuclear Power Catalytic splitting H2 + O2

Purple/Pink Nuclear Power Electrolysis H2 + O2

Yellow Solar Power Electrolysis H2 + O2

Green Renewable Electricity Electrolysis H2 + O2

As the hydrogen economy evolves and technology develops and matures other processes and colours may be utilised. It must also be noted that not everyone around the world agrees on the naming scheme, so local variations may exist. However, the information above is the most generally accepted view at the current time (late 2021).  Often colours are grouped together, and we explore why and how in more detail below. 

Colour grouping

Often for "simplicity" (but perhaps confusing to those new to hydrogen), colours are grouped together under one colour banner as they share many attributes.

Brown hydrogen

Brown is used by many in industry to cover Brown, Black and Grey hydrogen all under one banner. All 3 processes take a fossil fuel from the ground and turn it into Hydrogen gas, releasing CO2 to the atmosphere. Generating hydrogen this always carbon positive.

Blue Hydrogen

Blue hydrogen similarly can be expanded to encompass any fossil fuels used as the energy source (rather than just natural gas) and just like Brown it too generates CO2. The key difference with Blue Hydrogen is that developing technologies are then used to capture a proportion of the generated CO2 and store it, often underground. The carbon intensity of this process can vary significantly and capture technologies at larger scales are an area of significant development. Blue hydrogen does have the potential to be a low carbon fuel.

Green Hydrogen

Green hydrogen uses a renewable energy source (wind, solar, tidal etc) to generate electricity. This electricity is used to split water (H20) via electrolysis into Hydrogen and Oxygen gases (H2 and O2). This process generally results in a low carbon fuel.

I hope that this brief high-level tour of the hydrogen colour spectrum gives you an greater appreciation of some of the potential sources of hydrogen to power your projects.

If you'd like to discuss a possible hydrogen project with our rail team then please get in touch via the form and we'll put you on the right track.