top of page

Guide to the Types of Hydrogen Colors

Hydrogen periodic table symbol in multiple colors

What are the different types of hydrogen colors and what do they mean? What type of hydrogen fuel is produced from the different sources? What are the implications on hydrogen quality monitoring based on the source? These questions are answered and much more!

The different hydrogen colors are a shorthand to indicate the source and/or process of the hydrogen. The different colors can also be indicative of the type and amount of emissions and thus one can estimate the contribution to the Zero emissions target.

In summary, the different colors of hydrogen are: green, gray, blue, white, black, brown, red, pink, yellow, and turquoise.

From these, the most popular forms of hydrogen are: green, gray and blue. This is mainly due to the high availability of the source of hydrogen and the accumulated knowledge in the production of hydrogen leading to these types.

Green Hydrogen

Green hydrogen, also known as renewable hydrogen, is called ‘green’ because the process for producing it is the most environmentally-friendly. Because green hydrogen is made from entirely renewable energy, there are no pollution emissions. Thus, it is the most sustainable form of hydrogen.

Green hydrogen is produced from electrolyzers relying on a chemical process (electrolysis) that separates the hydrogen and oxygen molecules that make up water. The energy input required for the process relies on renewables like solar and wind.

While green hydrogen from electrolysis is already being used across the world, it’s still at a high economic cost since electrolyzers are not produced at a mass scale. Market drivers lead to the expectation that this cost will go down in the next few years, similar to the way that photovoltaic panels cost 9x less today than they did about 10 years ago.

To date, electrolyzer systems cost somewhere between $650 and $900 per kW. However, the total costs of having an electrolyzer include other components not included in this price, such as a drier, a cooler, systems for de-oxo and deionization, as well as the connection to the electricity grid, and civil works. These additional costs are about 45% of the total CAPEX. Thus, costs ultimately range from $1,000 to $1,400 per kW. Estimates have shown that every time that the global installed capacity doubles, electrolyzer CAPEX can decrease by about 11%. This means that by 2030, the CAPEX for electrolyzers can fall to $340 per kW.

Green Hydrogen Producers & Hydrogen Quality Monitoring

In this category, we include low-medium hydrogen producers who produce hydrogen at the range of 100-1000 Kg/day. This category includes distributed hydrogen production facilities mostly using electrolyzers.

These producers need to comply with the strict requirements of ISO-14687 when selling hydrogen for mobility, however they usually don't have in-house laboratories with state-of-the-art analytical equipment, rather they use innovative solutions and in-line analyzers. While ISO-14687 defines the maximum allowed concentration of 13 contaminants, with carbon monoxide, sulfur compounds and ammonia among them, green hydrogen producers and sellers usually only request to monitor oxygen and humidity levels. This is due to the risk assessment they performed which points on these two (oxygen and humidity) as the most likely to occur according to source and production. NanoScent's VOCID® H2Confirm is aimed at providing a targeted solution for this sector through the continuous analysis of oxygen and humidity at the ISO level, simultaneously.

Sometimes, green hydrogen producers also supply the hydrogen at the point of production, in this case they monitor a wider range of contaminants that are significant for end users, e.g. fuel cell users. This set-up can be found in hydrogen refueling stations (HRSs) such as the public HRS in Veldhoven, Netherlands which is operated by Total Energies.

Table explaining the hydrogen colors green, blue and gray based on the source and process.

Gray Hydrogen

Gray hydrogen is the most common type of hydrogen produced today. Estimates show that about 96% of all hydrogen produced today is classified as gray hydrogen. Source

Gray hydrogen is not environmentally-friendly since methane is used via a process called steam methane reforming (SMR) to produce it, a process that comes with a lot of carbon emissions.

The process for creating gray hydrogen puts about 9 kilograms of carbon dioxide into the atmosphere for every kilogram of hydrogen produced. In 2019, it was estimated that 2% of global carbon emissions come from gray hydrogen.

Gray Hydrogen Producers & Hydrogen Quality Monitoring

Most hydrogen production currently relies on big and centralized refineries that use gas steam reforming to produce hydrogen. They have the capacity to produce more than 8 tons of hydrogen per day for general industrial purposes with approximately 7 tons of high standard hydrogen per day used for sensitive industries like semiconductor and mobility.

Hydrogen producers and sellers are required to comply with different standards and regulations according to the use case for which the hydrogen is used (e.g. semiconductors, food and beverages, mobility etc.).

In order to comply with the strict standard requirements, hydrogen producers and sellers measure the quality of the hydrogen they produce either in their process line or in an analytical lab. They usually test their lines in an analytical laboratory once a day or after maintenance. The in-line analyzers are used to continuously measure specific analytes in the process line directly related to process control or to the quality of the product they manufacture. The measurements are performed at a frequency of minutes or even seconds, however the analyzers are usually limited to one or maximum two contaminants, costly and sometimes have low reliability.

Blue Hydrogen

Blue hydrogen is also created from methane via SMR, just like grey hydrogen is. The key difference is that blue hydrogen utilizes carbon capture and storage (CCS) technology which captures the carbon emissions during SMR instead of releasing them into the atmosphere. It is estimated that for every 1 kg of hydrogen produced, carbon emissions fall to 1.5 - 5 kg of CO2, depending on how much CCS is used.

If you capture 90% of the carbon emissions through the blue hydrogen process, that makes it very difficult to see a world where blue can be a significant part of Net Zero when you are getting to 2050 levels of target. It should very much be part of the next 10 years.
If you could get that capture rate up to 98% or 99%— that is a fantastic innovation engineering challenge and is not straightforward it suddenly becomes much more valuable to do it.

- Guy Newey from Energy Systems Catapult; Source: Science & Technology Committee, UK

While this type of hydrogen is considered to be more environmentally-friendly than gray hydrogen, but not as much as green hydrogen is. Since gray hydrogen is the most abundantly produced, as mentioned previously, blue hydrogen plays an important role in reducing the carbon emissions of the production process. Because of this, many see blue hydrogen as a stepping stone or a short term solution and green hydrogen as the long-term goal. Examples of companies that are pursuing blue hydrogen production include BP and Uniper / Shell.

Since blue hydrogen is produced the same way as gray hydrogen, they have the same needs for monitoring hydrogen quality when it comes to quantifying contaminants.

Other Types of Hydrogen Colors

Infographic of the different types of hydrogen colors

There are also other colors or types of hydrogen, described below:

  • White Hydrogen: White hydrogen is naturally occuring, found present from geological sources.

  • Black Hydrogen: Black hydrogen is produced from bituminous coal via coal gasification.

  • Brown Hydrogen: Brown hydrogen is made via coal gasification, specifically lignite coal. This type emits more than 20 kg of CO2 for every 1 kg of hydrogen.

  • Red Hydrogen: Red hydrogen comes from nuclear power, but instead of being used for electrolyzers, it goes into the electricity grid, then electricity is used to make hydrogen. Some sources also say that red hydrogen comes from biomass.

  • Pink Hydrogen: Pink hydrogen is made from nuclear power that is then directly used by electrolysis processes.

  • Yellow Hydrogen: Yellow hydrogen can come from a mix of sources from the electrical grid but is most commonly produced using solar power.

  • Turquoise Hydrogen: Turquoise hydrogen is a relatively new type of hydrogen which is made from methane pyrolysis.


The description of hydrogen by color is a way for those active in the hydrogen industry to quickly communicate with each other about the production processes that create the hydrogen. The color distinctions are important as they not only reveal the source, but also the associated carbon emissions that come with the production method. Hydrogen is considered to be a futuristic fuel with a promise to be free of carbon emissions, thus green hydrogen is the most environmentally friendly. As there are many different types of production methods, it is important for producers to monitor the hydrogen quality to be contamination-free in order to ensure that the fuel can be usable for end-consumers.


bottom of page