You’ve likely seen articles defining hydrogen as blue, green, black, yellow, pink, turquoise, or myriad other colours, but what do these colours mean? Isn’t hydrogen a colourless gas?
Don’t fret, your high-school chemistry isn’t failing you. These colours describe the method in which hydrogen is produced and its environmental impact (specifically the carbon footprint), the gas itself remains colourless.
At either end of this colour spectrum are green and black hydrogen, with the other colours somewhere in between:
- Green: the cleanest method, achieves carbon neutrality via the electrolysis of water using renewable electricity
- Black: the most environmentally damaging production method uses the gasification of coal. It not only releases CO2 but also carbon monoxide
- Grey: currently the most common method; uses fossil fuels in steam methane reforming, releasing large amounts of CO2. Also refers to hydrogen produced via water electrolysis using non-renewable power.
- White: generated as a by-product of another process. Can also refer to naturally occurring hydrogen
- Turquoise: produced using methane pyrolysis. Produces carbon as a solid rather than as a gas, simplifying capture.
- Blue: H2 produced through steam methane reforming (similar to Grey hydrogen), where CO2 emissions are captured through Carbon Capture and Storage.
- Red: high temperature catalytic splitting of water molecules using nuclear power’s thermal energy
- Pink: uses nuclear sources of electricity to power the electrolysis of water
- Purple: combines nuclear power and heat into a chemo-thermal electrolysis splitting of water
- Violet: same as purple
- Yellow: water electrolysis powered by solar electricity
- Brown: used interchangeably with black, especially when denoting the type of coal used in the process
As the hydrogen industry continues to grow and its stronghold as a key component of the new cleantech economy strengthens, this colour-coding system will continue to evolve. New methods (and colours) will be added, existing ones will fall out of favour, cementing the key role hydrogen production will have in achieving Net Zero.