As you may already know, hydrogen is an odourless, colourless gas. However, with a little bit of human intervention, it is now multi-coloured.
These colours are related to how the Hydrogen is generated and hence defines its Eco-friendly credentials. Here are some definitions of the most common (and a few more exotic) colours:
Black or Brown Hydrogen – these are the hydrogens gassified from fossil fuels, specifically coal (either lignite or black coal, being named brown and black hydrogen respectively). The CO2 from this process is released into the atmosphere.
Grey Hydrogen – made from steam reformed natural gas without carbon capture and storage (CCS). As with Black and Brown Hydrogen, CO2 generated through this process is released into the atmosphere.
Blue Hydrogen – made from natural gas through the process of steam methane reforming. Whilst CO2 emissions are generated, these are either managed through offsetting or technical abatement (carbon capture and storage - CCS). Blue hydrogen is effectively Grey Hydrogen, but with the CO2 from the process captured and stored.
Turquoise Hydrogen – produced from natural gas using molten metal pyrolysis technology. The natural gas is passed through molten metal that releases the hydrogen as well as solid carbon. The carbon dioxide from this process is produced in solid form, so little / no atmospheric release, but still presents an issue of with what to do with the solid form.
Green Hydrogen – uses a big electrolyser, copious amounts of water and plentiful supplies of electricity; where the electricity comes from a renewable source (nuclear, solar or hydro).
Some organisations break down green Hydrogen further by its renewable source, so:
Pink Hydrogen refers to hydrogen generated through electrolysis powered by nuclear energy; and
Yellow Hydrogen to hydrogen generated through electrolysis powered by solar energy.
There is one final “colour” of hydrogen; White Hydrogen is that which is naturally occurring geological hydrogen found in underground deposits and created through fracking, although at this time there are no viable exploitation strategies for this.