A recent study led by a petroleum geochemist at the U.S. Geological Survey suggests that 5.6 trillion metric tons of hydrogen gas could be buried beneath the Earth’s surface in rocks and underground reservoirs:
The study published in Science Advances predicts a wide range of values for the potential in-place hydrogen resource (103 to 1010 million metric tons (Mt)) with the most probable value of ~5.6 × 106 Mt. Although most of this hydrogen is likely to be impractical to recover, a small fraction or two percent (e.g., 1 × 105 Mt) would supply the projected hydrogen needed to reach net-zero carbon emissions for ~200 years.
This amount of hydrogen contains more energy (~1.4 × 1016 MJ) than all proven natural gas reserves on Earth (~8.4 × 1015 MJ).
Whether or not hydrogen exists in such quantities is not relevant. Hydrogen cannot be liquified, except by very expensive cryogenic processes. So even at high pressure it had a low energy density.
Moreover there is the issue of embrittlement, especially of steel. This means hydrogen cannot be stored in pressure vessels or transported in pipelines. Hydrogen must be used where it is generated, most likely to generate electricity. This means that if hydrogen is a diffuse source, it is unusable. The is the same problem with gold in the ocean and metals in the asteroid belt: they are economically unrecoverable.
Next you will be telling me wind, waves, tides, and sunlight are free energy sources.
There are high-strength embrittlement-resistant alloys. Copper-beryllium, for instance, seems almost totally immune, and has extremely low hydrogen solubility and diffusivity. It also has a tensile strength that, at >1400MPa, surpasses even some of the so-called “ultra high-strength” steels. Beryllium isn’t really that scarce, so Cu-Be could possibly work for pressure vessels or as pipeline cladding.