Turquoise, green, blue – the colors evoke images of a beautiful sea. Granted, other designations include grey, RED II and carbon-neutral. They all refer to hydrogen, which is increasingly becoming the focus of attention. In the media, hydrogen is closely associated with the energy transition and discussed as an alternative energy carrier. I myself have not been able to classify hydrogen so far. Let’s give it a try then:


Do you remember the periodic table of elements from chemistry class? The ordinal numbers? Hydrogen, or H for short, has the atomic number 1 and is at the top of the table, which in turn is on page one of every chemistry book in Germany. It is the most common element in the universe and is found in many compounds, for example in water, known as H2O. But why is a 2 attached to it, i.e. H2?

Policy framework

H stands for the hydrogen atom and H2 for a colorless and odorless gas – more specifically: a hydrogen gas. And the latter is relevant for the energy transition. Using hydrogen gas is intended to reduce the use of fossil fuels. In principle, H2 is conceivable as an energy carrier in transport, buildings or industry. In the chemical industry, for example, hydrogen has long played a role as a secondary energy carrier. It is a hot topic – and policymakers have reacted, as has TÜV Rheinland:

On 9 July 2020, the German National Hydrogen Council met for its constituent meeting, initiated by the Federal Ministry for Economic Affairs and Energy. The goals of the National Hydrogen Strategy include establishing hydrogen from renewable energies, creating a regulatory framework and strengthening the German economy by promoting research. TÜV Rheinland, in turn, founded the Hydrogen Competence Center at the start of the year. Our goal is to provide technical support for the development and provision of hydrogen services along the value chain – from production to application.

The hydrogen color scheme

Back to basics: How is hydrogen produced? How does it become energy? Hydrogen can be produced by various processes. And depending on the production method, it is assigned a color.

Green hydrogen

Green hydrogen is carbon-neutral because it is produced by electrolysis of water using only electricity from renewable energy sources.

Blue hydrogen

Blue hydrogen is produced from fossil fuels. One process for this is steam reforming. In theory, this would release CO2 into the atmosphere. However, in this process, the CO2 produced is captured and stored. This technique is called carbon capture and storage (CCS). This production method is also considered carbon-neutral overall.

Turquoise hydrogen

Turquoise hydrogen is produced when natural gas is broken down into hydrogen and solid carbon using methane pyrolysis. Although this process does not produce CO2, the costly extraction of the natural gas is a significant factor.

Grey hydrogen

Grey hydrogen is produced by steam reforming of fossil fuels such as coal or natural gas. The resulting CO2 is emitted unused.

So much for the colors. Another way to classify hydrogen is determining whether it is carbon-neutral or not. Carbon-neutral hydrogen can be either green or blue, but its carbon footprint must be “zero” or less. While RED II also sounds like a color, it actually means carbon-neutral hydrogen that meets additional criteria of the Renewable Energy Directive II (RED II) – or Directive (EU) 2018/2001 on the Promotion of the Use of Energy from Renewable Sources.

TÜV Rheinland Standard H2.21 Carbon-Neutral Hydrogen

Certification with test mark: I am always in awe when my colleagues unveil a new set of rules. They really know their stuff, develop standards and find solutions. And they published test criteria for hydrogen too: The TÜV Rheinland Standard is called H2.21 Carbon-Neutral Hydrogen After successful certification, they verify that hydrogen has been produced using a carbon-neutral process.

There are opportunities to keep the carbon content low or offset it along the entire hydrogen supply chain. That’s why my colleagues look at the production process from start to application in their certification process. If certification is successful, our customers receive our test mark – both nationally and internationally, of course. It is a visible sign that companies like to share. But our competence center adopts a much broader approach than just certification. Around 50 colleagues deal with hydrogen from different perspectives: from industrial testing to mobility applications, product testing and system certification to training and occupational health and safety.


Nicole Krzemien

Nicole Krzemien

Social Media Manager + Spokeperson

Every day she is fascinated anew by her diverse job and her expert colleagues. She is eager to learn and tries to incorporate innovations into her everyday life. She loves the balancing act between work and family, enjoys being on or near the water and reads even more than she writes.

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