When they talk about hydrogen as a fuel, they assign it different colors, such as green, blue, and gray, depending on how pure it is.
Hydrogen is a colorless gas. We can use blue or green when visualizing hydrogen molecules, but it’s more for aesthetics.
So why all this talk about the different colors of hydrogen? These codes are used when it comes to using hydrogen as a fuel source.
Hydrogen as a fuel
In a world plagued by greenhouse gas emissions and fuel shortages, hydrogen has long been called a promising solution for the future. The hydrogen economy is seen as a way to combat the wide range of negative effects associated with traditional fuel consumption.
This is why hydrogen seems so appealing when it comes to reducing carbon in our energy systems. Hydrogen really deserves all the hype. There are no emissions when using it, but that is not necessarily the case when producing it.
To assume that hydrogen fuel is always one hundred percent environmentally friendly would be a mistake.
Hydrogen is an energy carrier. It is not a source of fuel. Hydrogen fuel ultimately acts as a carrier to store and deliver energy from other sources, and there are many ways to produce hydrogen fuel. The different methods rely on different sources and have their pros and cons. These primary sources affect the “purity” of the final product.
Consequently, not all hydrogen is the same. At the final point of use, hydrogen produces no emissions and is carbon-neutral, but the same cannot be said for most of the methods used to produce hydrogen today. Only a small fraction of all the hydrogen produced is truly clean.
Depending on the production method, the impact of hydrogen production varies from minimal/weak to a greater cause for concern.
The different colors of hydrogen
It is important to note here that hydrogen color codes are not yet standardized worldwide. Different countries, organizations, and authors use different codes with different numbers of colors.
Green Hydrogen
Green hydrogen is the hydrogen that is the purest of all. This hydrogen is produced mainly by electrolysis. Electricity is passed through water, causing it to split into hydrogen and oxygen. No harmful greenhouse gases are produced.
What makes it really clean, moreover, is that the electricity used for electrolysis is produced from renewable sources, such as the sun or wind. Clean electricity gives us really clean hydrogen.
Blue hydrogen
Blue hydrogen is produced from natural gas and other fossil fuels. Steam conversion of methane is used to extract hydrogen from these sources. Fossil fuels containing methane react with the steam to produce hydrogen and other byproducts.
Compared to other methods, this method is better because it uses a process called carbon capture and storage. This significantly reduces emissions. The hydrogen produced is low-carbon, but by no means carbon-neutral.
Gray hydrogen
Gray hydrogen is the “dirtiest” form of hydrogen fuel because the main energy source is fossil fuels. Coal is the most widely used for this purpose. The use of fossil fuels means that carbon dioxide is released as a byproduct. This uses steam conversion, the same as the production of blue hydrogen. The key difference is that no carbon capture and storage methods are used, so the emissions are about twice as high as for blue hydrogen.
Production of gray hydrogen is the cheapest and most common today. However, these production methods mean that gray hydrogen, even if it is the same as others at the end point of use, is not much better than traditional fossil fuel use.
Other colors
According to some, electrolysis using electricity from a nuclear power plant also produces green hydrogen. Others categorize it separately as pink hydrogen or purple hydrogen. Hydrogen produced by electrolysis using electricity from the grid is often referred to as yellow hydrogen.
Blue hydrogen is also often separated into turquoise hydrogen. The difference here is that instead of steam conversion, methane is pyrolyzed. As a byproduct, solid carbon is produced, which is considered a better alternative.
Some classifications further divide gray hydrogen into brown hydrogen and black hydrogen, depending on the type of coal used.
In addition, white, aqua, and other colors are occasionally found in this new area of scientific literature.
Green hydrogen for a greener future
Obviously, it is in everyone’s interest to produce as much carbon-neutral, green hydrogen as possible.
Unfortunately, the unfortunate details of economics make it impossible to do this right now. Electrolysis is difficult to make financially feasible on a large or industrial scale.
In addition, there are many uncertainties and ambiguities about how the purity of hydrogen is measured. There is no established standard for how different colors are determined or what aspects of hydrogen are taken into account in its estimation. Science and policy must go a long way and work together to make hydrogen fuel truly clean for a brighter future.
