Colours
of Hydrogen

Understanding Hydrogen's Rainbow: 

Hydrogen, a versatile energy carrier, is gaining traction as a potential solution for decarbonization.

However, not all hydrogen is created equal. The colour-coding system helps distinguish between production methods and their environmental impact.  The following describe the various generally accepted colour coding convention for the various production methods arraanged in order of percieved sustainability.

1. Grey Hydrogen

This is the most common form of hydrogen production. It involves steam methane reforming (SMR), where natural gas is reacted with high-temperature steam to produce hydrogen, along with significant carbon dioxide (CO2) emissions.

Grey hydrogen has a high carbon footprint, contributing to greenhouse gas emissions and climate change.

Essentially, this process is just using natural gas, and creating CO2, and therefore does little to help with decarbonization.

2. Blue Hydrogen

Blue hydrogen also relies on SMR, but with the addition of carbon capture and storage (CCS) technology. This aims to capture the CO2 emissions produced during the process and store them underground.

Blue hydrogen has a lower carbon footprint than grey hydrogen, but its sustainability depends on the effectiveness of CCS.

The effectiveness and long-term security of CO2 storage are subject to debate. Methane leakage during natural gas extraction and transport is also a concern. Additionally, not all CO2 is captured, and the processes to capture the remaining CO2, can be very energy intensive.

3. Turquoise Hydrogen

Turquoise hydrogen is produced through methane pyrolysis, which splits natural gas into solid carbon and hydrogen. This process, when powered by renewable energy, can significantly reduce emissions.

If the heat used in the pyrolysis is generated from renewable sources, this method can be considered relatively low-carbon. The solid carbon by-product has potential applications in various industries.

The scalability and economic viability of methane pyrolysis are still being explored. The usage or safe disposal of the solid carbon is also a factor to consider.

4. Green Hydrogen:

Green hydrogen is produced through electrolysis, using renewable electricity (solar, wind, hydropower) to split water into hydrogen and oxygen.

Green hydrogen is considered the most sustainable option, as it produces zero greenhouse gas emissions during production.

The cost of renewable electricity and electrolyzers is a significant barrier to widespread adoption. The availability of freshwater for electrolysis can also be a concern in some regions.

5. Pink/Purple/Red Hydrogen:

This category refers to hydrogen produced through electrolysis powered by nuclear energy. Pink
hydrogen refers to electrolysis powered by nuclear electricity. Purple or red hydrogen refer to hydrogen produced by high temperature steam electrolysis powered by nuclear heat.
Nuclear energy is considered low-carbon, making this method a sustainable alternative to fossil fuel-based hydrogen production.

Public perception of nuclear energy and concerns about nuclear waste and safety are factors. The availability of nuclear power plants and the cost of nuclear electricity are also considerations.
Important Notes:

The colour-coding system is a simplified way to categorize hydrogen production methods. There are ongoing discussions and refinements to the definitions, and not all industry figures fully agree on all definitions. The overall "cleanness" of any hydrogen production method is dependant on the entire life cycle of the process.

By understanding the different colours of hydrogen, we can make informed decisions about its role in a sustainable energy future.