Basics of Fuel Hydrogen
From our Print Issue 2nd March 2022 of Enviro Annotations
Hydrogen is widely considered to be a clean fuel that, when consumed in a fuel cell, produces only water. Hydrogen can be produced from a variety of domestic resources, such as natural gas, nuclear power, biomass, and renewable power like solar and wind. These qualities make it an attractive fuel option for transportation and electricity generation applications. It can be used in cars, in houses, for portable power, and in many more applications. It takes energy to produce molecular hydrogen. The source of energy and the production method used to make molecular hydrogen determines whether it’s classified as grey hydrogen, blue hydrogen or green hydrogen.
Grey hydrogen is hydrogen produced using fossil fuels such as natural gas or coal. Grey hydrogen accounts for roughly 95% of the hydrogen produced in the world today. The two main production methods are steam methane reforming and coal gasification. Both of these processes release carbon dioxide (CO2). If the carbon dioxide is released into the atmosphere, then the hydrogen produced is referred to as grey hydrogen. Grey hydrogen is not considered a low-carbon fuel.
Blue hydrogen is similar to grey hydrogen, except that most of the CO2 emissions are sequestered (stored in the ground) using carbon capture and storage (CCS). Capturing and storing the CO2 instead of releasing it into the atmosphere allows blue hydrogen to be a low-carbon fuel. The two main production methods are steam methane reforming and coal gasification, both with carbon capture and storage. Blue hydrogen is a cleaner alternative to grey hydrogen, but is expensive since carbon capture technology is used.
Green hydrogen is hydrogen produced using electricity from clean energy sources. Green hydrogen is considered low or zero-emission hydrogen because it uses energy sources such as wind and solar which don’t release greenhouse gases when generating electricity. Green hydrogen is made when water is split into hydrogen and oxygen. Water splitting is also known as electrolysis, and requires an energy input. The method of supplying electricity to split water is an expensive process, but much more environmentally-friendly compared to the production of grey hydrogen.
In the energy industry, other colours are also used to differentiate between the types of hydrogen. Although grey, blue and green are most common colours, black, brown, red, pink, yellow, turquoise and white exist as colours for molecular hydrogen.
Colours such as black and brown are more specific types of grey hydrogen. Black hydrogen is when black coal is used usually in a gasification process to make hydrogen. Brown hydrogen is when lignite (brown coal) is used to make hydrogen.
Red hydrogen is made from biomass. Biomass can be transformed to produce hydrogen via gasification. Depending on the type of biomass and the use of carbon capture and storage technologies, red hydrogen can have lower CO2 emissions than grey hydrogen. If the CO2 is completely captured and there are no other emissions, it can be considered green hydrogen.
Pink hydrogen refers to hydrogen generated through electrolysis powered by nuclear energy. Pink hydrogen is usually considered green because it does not produce and CO2 emissions during operation.
The colour yellow sometimes indicates hydrogen produced via electrolysis through solar energy. An upcoming colour of hydrogen is turquoise hydrogen, although it has yet to be proven at a large scale. Turquoise hydrogen is made using a process called methane pyrolysis to produce molecular hydrogen and solid carbon.
In addition, there is what’s called white hydrogen. In nature, we find hydrogen in gaseous form and it is colourless. That is why, when you hear about white hydrogen, it refers to naturally occurring geological hydrogen that might be rarely found in underground deposits. There aren’t any viable strategies to use these deposits now, which is why different processes are being applied to generate hydrogen artificially — gasification, electrolysis, methane pyrolysis, et al.