Waterguide – Colours of hydrogen

Why can hydrogen be colourful?

Hydrogen is basically a colourless and odourless gas. Nevertheless, various colours appear in the context of hydrogen and the future of energy production. What is behind them?  

Germany intends to be climate-neutral by 2050. Hydrogen is expected to play an important role as an energy source. The reason for this is that no greenhouse gases are produced during combustion. Various methods currently exist for the production process. In most cases, electrolysis uses electricity to split water into its molecular components hydrogen and oxygen. For example, green hydrogen is produced by electrolysis of water using renewable energy sources such as wind or solar energy. It is then characterised as climate neutral.

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But not all hydrogen is the same. Whether green, blue, grey or turquoise, hydrogen has different names depending on how it is produced.

 

How is hydrogen used and what is the significance of the colour?

There are many possible applications for hydrogen. For example, hydrogen can be used to generate heat and electricity, or fuel cells can be used to power vehicles in the mobility sector. Hydrogen can also be used as a raw material in industrial processes and thus contribute to the decarbonisation of energy-intensive sectors such as the steel industry. Hydrogen is also an efficient storage medium for electricity from renewable energies, which is generated on windy and sunny days and not consumed.  

The type of hydrogen production is distinguished by colour. Currently, the following colour palette exists:

• White hydrogen: Basically, white hydrogen does not belong on this list, as it refers to the naturally occurring hydrogen found underground. So far, very little reliable data is available on global deposits and possible extraction methods. The advantage of commercial utilisation would be ‘natural’ climate neutrality.
• Grey hydrogen: It  is produced from fossil fuels using a process known as steam reforming. As a rule, natural gas is converted into hydrogen and carbon dioxide by adding heat. This process is already used in industry. However, it is associated with considerable CO₂ emissions.
• Blue hydrogen: Blue hydrogen is also produced using steam reforming. The resulting CO₂ emissions are captured using carbon capture and storage (CCS) and stored underground. This significantly reduces the CO₂ footprint of blue hydrogen and can be described as low emission.
• Green hydrogen: Green hydrogen is described as climate neutral. The reason for this is that electricity from renewable energy is used in electrolysis to split water into oxygen and hydrogen. The hydrogen produced is therefore produced without the emission of climate-damaging gases. The German government has launched a National Hydrogen Strategy (NWS) for the development and use of green hydrogen and sees it as a key pillar for a climate-neutral, sustainable future.
• Turquoise hydrogen: This production method is still in the testing phase. Turquoise hydrogen is produced by thermally splitting methane (methane pyrolysis). Instead of climate-damaging gases, solid carbon is produced that does not escape into the atmosphere. To be climate-neutral, the heat supply for the high-temperature reactor must come from renewable energy.
• Orange hydrogen: This form of hydrogen is produced based on waste, biomass and residual materials. It uses electricity from waste utilisation plants, for example, and is therefore not free of CO₂ emissions.
• Pink or yellow hydrogen: The hydrogen is produced by using nuclear energy. Although this makes it climate-neutral, it produces large quantities of radioactive waste that must be safely and permanently stored for thousands of years.
• Brown or black hydrogen: This is the "dirtiest" form of hydrogen. The reason for this is that electricity from brown or black coal is used to produce it.

 

You can find out more about green hydrogen here:

Water treatment for green hydrogen