Can hydrogen have different colors? From where do the different colors emerge? For what is the color coding of a gas useful? Such questions and many others might pop to your mind when you surf the web and come across one of the different colors of hydrogen. You’re probably tired of reading extensive explanations of the different colors and their origin, and this article is about to be your savior for the day!

The importance of hydrogen has been increasing through the past years, mainly because of its high impact in reducing emissions. In fact, hydrogen is the basis of many emerging green technologies, including fuel cell electric cars, which is the main reason for its increased consumption. To meet the increasing demand, the production of hydrogen at an industrial level has emerged to complement the naturally occurring hydrogen reserves. Although hydrogen naturally occurs as a colorless gas, different color codes have been associated to it to reflect the process or fuel from which it emerged. Moreover, there are around nine different colors associated to hydrogen, the most important ones enumerated and explained below along with the challenges associated to industrial hydrogen production.

What is white hydrogen?

The term white hydrogen refers to the naturally occurring gas that is produced from underground reserves and deposits through fracking. The extraction of this type of hydrogen could be done without any CO₂ emissions, and it has a competitive price compared to other industrial produced hydrogen regardless of the process.

What is green hydrogen?

Compared to other industrially produced hydrogen types, green hydrogen is the cleanest in terms of green house gas emissions, as the name “green” suggests. It is produced by the electrolysis of water using excess renewable energy. The process of electrolysis mainly uses solar and wind power to split water molecules into oxygen and hydrogen. This type of hydrogen production could be considered a way to store excess renewable energy for long periods of time. Moreover, the produced hydrogen could be directly consumed in its gaseous form, or it can be processed in a reverse reaction to obtain back electricity. For an example of large industrial scale hydrogen production from renewable energy check out this project developed in Amsterdam, H2ermes.

What is blue hydrogen?

Blue hydrogen is produced with methane as an input to the steam methane reforming process. Through this process, methane mixes with hot steam in the presence of a catalyst producing hydrogen and carbon monoxide. At a later step, water is added reacting with the carbon monoxide to result in carbon dioxide and more hydrogen. In case the CO₂ is captured through the carbon capture and storage process (CCS) , then the produced hydrogen would be referred to as blue. So, one can say that the term blue is referred to hydrogen when there are no emissions related to its production. For a more detailed explanation of the steam methane reforming process, refer to this explanatory video by the global hydrogen supplier HyGear. However, the entire production process of hydrogen, taking into consideration the starting input, methane, is not fully carbon neutral. On this point, some concerns arise related to the leakage of methane into the atmosphere during its extraction process. Moreover, there are some concerns related to leakages that could occur in underground storage of carbon dioxide.

What is grey hydrogen?

Grey hydrogen could be considered the opposite of both, green and blue hydrogen. It is the most polluting hydrogen. Most commonly, it is produced using the steam methane reforming process. Yet, in this case, the carbon dioxide produced is not captured and stored, but rather, it is released to the environment. Therefore, the use of hydrogen in this case defeats its purpose. The technologies that are based on hydrogen as a fuel are developed with the aim of reducing emissions, which is not reached in case grey hydrogen is used. Another way of obtaining grey hydrogen is by using non-renewable energy to perform the electrolysis of water. The production would be the same as green hydrogen, but, the energy used to perform the process would not be green, hence, obtaining grey hydrogen.

The above four hydrogen colors refer to the main and universal H₂ color codes. Other colors, described briefly below, might also come up when you go through readings related to hydrogen.

What is pink hydrogen?

In some cases, the electrolysis process is performed by using energy coming from nuclear power plants, resulting in pink hydrogen. This type of hydrogen is less common than other hydrogen forms, mainly due to widespread restrictions on further development of nuclear power plants. Nevertheless, one can confidently say that in the presence of nuclear plant, the production of pink hydrogen provides an attractive additional revenue stream for the plant, especially with the rising curtailment hours in some regions. This is true since the excess energy can be used to produce hydrogen, which could be either stored and transported or, processed again to produce electricity and feed it to the grid. This process does not produce any emissions, but concerns arise regarding the radioactive wastes produced by nuclear plants.

What is black or brown hydrogen?

As the names imply, black or brown hydrogen refer to H₂ gas produced from highly polluting energy sources such as coal. For example, hydrogen could be used through the gasification of coal and the result would be the emission of high amounts of carbon dioxide relative to the produced hydrogen quantity. This leads to the known “problem shifting” issue where the in most cases, the production of hydrogen and the use of hydrogen do not occur in the same region. Hence, the emissions would be generated in a certain country, and the produced hydrogen would be transported to another country which would be consuming low-emissions hydrogen. For example, this is the case between Australia and Japan where black hydrogen is produced in Australia and transported for use in Japan.

What are the challenges that face industrial hydrogen production?

Although hydrogen appears to be a promising technology for the shift towards cleaner energy sources, there are many challenges associated to its widespread adoption, including but not limited to:

• The production of hydrogen from low-cost sources is limited at the moment: For hydrogen to serve its desired purpose, it should be produced from green renewable energy. To date, the production of renewable energy is still costly relative to conventional energy sources leading to higher hydrogen prices. This might limit the diffusion of industrial hydrogen production, and therefore limit the adoption of technologies based on it. With the expected decrease in renewable energy, the adoption of hydrogen based technology would increase, and as a result, also the costs associated to such technologies would drop due to benefiting from mass production.
• The presence of the appropriate hydrogen infrastructure is still lagging: This is considered one of the major barriers to the adoption of hydrogen-based technologies especially in European countries. For instance, even though fuel cell cars offer promising kilometer range compared to other electric cars, their diffusion is rather limited mainly because of the extremely high costs associated to building hydrogen refueling stations.
• Governmental regulations do not support the further development of hydrogen: Unlike other green technologies which are supported by governmental subsidies to ensure their diffusion, hydrogen is one of the technologies which till now have not gained the required attention to ensure its expansion.

Conclusion

As a conclusion, hydrogen is an important enabler of the energy transition since, unlike renewable energy sources, it is an energy carrier which could be easily stored for longer periods of time and transported for remote use. Although it is still not commonly widespread, many start ups are trying to capture the value of this market at an early stage; the most known ones are:

• Green Hydrogen Systems: This Dutch start up is involved in developing large scale electrolysers. It has developed multiple electrolysers at the European levels in countries including Denmark, France and the Netherlands.
• Ergosup: This French start up has developed an innovative process to produce pressurized hydrogen enabling refueling fuel cell cars. One of their fully integrated charging stations is the Hyris Lab.

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