Making the planet decarbonised is one of the goals that countries around the world have set for 2050. Decarbonisation is an important step towards achieving this goal. As the world's energy demand grows, new solutions are emerging and starting to emerge, including green hydrogen.  What is green hydrogen and what makes it more sustainable? Green hydrogen is produced by electrolysis using renewable energy sources such as wind or solar power. Hydrogen produced without emitting carbon dioxide can be used in fuel cells to generate electricity, or burned in a mixture with natural gas to reduce CO2 emissions.

This energy carrier has universal applications and is relatively easy to produce. This form of hydrogen is produced by a chemical process known as electrolysis. It uses electricity to separate hydrogen and oxygen in water. When electricity is generated from renewable sources, it produces energy without releasing carbon dioxide into the atmosphere. As the IEA points out, this method of extracting green hydrogen can save 830 million tonnes of CO2 per year compared to producing this gas using fossil fuels. Currently, it would take 3000 TWh per year from renewable energy sources to replace all the world's grey hydrogen. Further questions have also been raised about its economics and viability. 

The rainbow colours of the names actually indicate the different technologies used to produce it. These colour codes are essentially nicknames used in the energy industry to distinguish between types of hydrogen. Depending on the type of production used, different colour names are assigned to hydrogen. However, there is no universal naming convention and these colour designations can vary over time and even between countries. Hydrogen is an invisible gas. So, despite their colourful descriptions, there is no visible difference between the different types of hydrogen.  Here’s our guide to unlocking the current hydrogen colour code.

Green hydrogen

Green hydrogen is produced by using clean electricity from renewable energy sources such as solar or wind power to electrolyse water. Electrolysers use an electrochemical reaction to separate water into its hydrogen and oxygen components, and emit zero carbon dioxide in the process. Green hydrogen currently accounts for a small percentage of total hydrogen because it is expensive to produce. As the price of energy from wind power has fallen, so will the price of green hydrogen as it becomes more widespread.

Blue hydrogen

Blue hydrogen is produced mainly from natural gas, using a process called steam reforming, which brings together natural gas and heated water in the form of steam. The output is hydrogen, but carbon dioxide is also produced as a by-product. So, the definition of blue hydrogen includes the use of carbon capture and storage (CCS) to trap and store this carbon. Blue hydrogen is sometimes described as ‘low-carbon hydrogen’, as the steam reforming process doesn’t actually avoid the creation of greenhouse gases.
 
Grey hydrogen

Currently, this is the most common form of hydrogen production. Grey hydrogen is created from natural gas, or methane, using steam methane reformation but without capturing the greenhouse gases made in the process. Grey hydrogen is essentially the same as blue hydrogen, but without the use of carbon capture and storage.

Black and brown hydrogen

Using black coal or lignite (brown coal) in the hydrogen-making process, these black and brown hydrogen are the absolute opposite of green hydrogen in the hydrogen spectrum and the most environmentally damaging. Just to confuse things, any hydrogen made from fossil fuels through the process of ‘gasification’ is sometimes called black or brown hydrogen interchangeably. Japan and Australia announced a new brown coal-to-hydrogen project recently. This project will use brown coal in Australia to produce liquefied hydrogen, which will then be shipped to Japan for low-emission use.

Pink hydrogen

Pink hydrogen is generated through electrolysis powered by nuclear energy. Nuclear-produced hydrogen can also be referred to as purple hydrogen or red hydrogen. In addition, the very high temperatures from nuclear reactors could be used in other hydrogen productions by producing steam for more efficient electrolysis or fossil gas-based steam methane reforming.

Turquoise hydrogen

This is a new entry in the hydrogen colour charts and production has yet to be proven at scale. Turquoise hydrogen is made using a process called methane pyrolysis to produce hydrogen and solid carbon. In the future, turquoise hydrogen may be valued as a low-emission hydrogen, dependent on the thermal process being powered with renewable energy and the carbon being permanently stored or used.
 

Yellow hydrogen

Yellow hydrogen is a relatively new phrase for hydrogen made through electrolysis using solar power.
 

White hydrogen

White hydrogen is a naturally occurring, geological hydrogen found in underground deposits and created through fracking. There are no strategies to exploit this hydrogen at present.

Hydrogen as a fuel is playing an increasingly important role in the world. Some countries are making significant progress in its use, while others, such as Japan, are going further and aiming to become a hydrogen-based economy.