Hydrogen plays an important role in the energy transition. The reasons are straightforward: hydrogen is nowadays employed on a large scale in a variety of industries such as the steel industry. In some industrial processes hydrogen is simply indispensable. Yet currently some 90% of this hydrogen is produced from fossil fuels (usually natural gas) with the release of green house gases as a result. Hydrogen produced in this way is known as grey hydrogen.
Producing hydrogen in a more sustainable way is thus a way to realize climate goals on global level. Yet it is not immediately clear how to approach the task of giving up hydrogen produced from fossil fuels with release of CO2. Two courses of action have spurred some discussion lately in expert and policy circles.
Blue hydrogen is the hydrogen that is produced in much the same way grey hydrogen is produced but the CO2 (not all) is captured and stored or reused so that it is not released into the atmosphere.
Green hydrogen is the hydrogen that is produced through a process known as 'water electrolysis'. Basically, an electric current is run through water until oxygen and hydrogen are separated. With the exception of heat and some small remnants, this process releases no CO2 into the atmosphere.