The hydrogen rainbow is a term used to describe the different types of hydrogen that either exist naturally or are produced through man-made processes. Differentiating between these types is important for understanding where they come from and how they affect the environment. Below, we discuss the main colors you can expect to hear about in the industry.
Currently the most common form of man-made hydrogen, grey hydrogen is derived from natural gas using steam methane reformation. This process involves the combination of natural gas and water (steam) to produce hydrogen, while also creating carbon dioxide as a byproduct. Carbon emissions that are created are neither captured nor stored.
Blue hydrogen relies on the same reformation process as grey hydrogen, but includes a means of trapping its subsequent greenhouse gasses. This is why it’s sometimes referred to as “low-carbon hydrogen,” as the CO₂ it emits is captured, keeping it from entering the atmosphere.
As its name might imply, this is considered the most eco-friendly hydrogen option on the market today, due to the fact that its only additional byproduct is oxygen. This is because green hydrogen utilizes energy from a combination of renewable sources like wind, solar, and hydropower to perform electrolysis on water. Both green and blue hydrogen are also referred to as clean hydrogen due to their little to no emissions.
Note: You may also hear the term yellow hydrogen to describe hydrogen that is produced from solar-powered electrolysis. The difference between it and green hydrogen is that the former comes strictly from solar power, while the latter is produced from a combination of renewable energy sources.
Because green hydrogen production is more costly than other types, it isn’t as widely adopted. However, projections are that it’s only a matter of time before the technology involved with its production is further refined, along with the necessary infrastructure, following a similar trajectory that natural gas took to become a valuable alternative fuel.
Pink hydrogen is similar to green hydrogen because it is also the result of electrolysis, but differs from its energy source — in this case, nuclear power. (It’s also notable that nuclear power has the potential to be applied to other types of hydrogen production listed above.)
Brown and Black Hydrogen
These types of hydrogen are both produced from the gasification of coal — brown from lignite, and black from bituminous — which makes them a heavy source of pollution and long-term environmental impacts.
This type is relatively new, and describes hydrogen that is produced through methane pyrolysis — or the thermal decomposition of methane into hydrogen and solid carbon. Cummins notes that if the thermal process could be powered by renewable sources, there is arguable potential for turquoise hydrogen to become a low-emission solution.
This is naturally occuring hydrogen found in geologic pockets. Hydrogen Fuel News highlights several ways that white hydrogen is produced, including:
- Serpentinization, a reaction between ultrabasic rocks and water
- Degassing H2 found deep within the Earth’s crust and mantle
- Weathering, in which water interacts with freshly exposed rock surfaces
- A contact between water and reducing agents located in the Earth’s mantle
- Organic matter decomposition
- Hydroxyl ion decomposition in the structure of minerals
- Natural water radiolysis
- Biological activity (Hydrogen Fuel News, Unveiling the Mysteries of White Hydrogen: The Ultimate Guide, 2022)
While considered pure and free of emissions, white hydrogen is also difficult to extract, and is not currently considered a viable resource based on the tools and processes available.
Do You Have Hydrogen Vehicles?
While it’s good to know where different types of hydrogen are developed, it’s also important that your team understands how to inspect and maintain fleet vehicles that run on it. That’s why we’ve developed these courses to help yours! Avoid vehicle downtime, reduce maintenance costs, and improve safety by enrolling your technicians today.
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