"Free hydrogen" refers to hydrogen gas that is not bound to any other element or compound. It is in its purest form and can be found naturally in the atmosphere or produced through various processes. Full definition
There's also a $ 499 lease that includes free hydrogen. (extremetech.com)
When coal is used to produce hydrogen it serves only as a source of the energy needed to break the water molecules into free hydrogen and oxygen atoms. (ramblingsdc.net)
The new model calculates the amount of free hydrogen gas produced and stored beneath the seafloor based on a range of parameters — including the ratio of a site's tectonic spreading rate to the thickness of serpentinized rocks that might be found there. (sciencedaily.com)