Looks like the only way hydrogen as a fuel makes sense is to produce it using electricity from a clean source like solar or nuclear.
In my mind, though, hydrogen is a dangerous gas.
If you have large amounts of solar or nuke power you can capture CO2 from the air or seawater add in the hydrogen from electrolysis run the reverse water gas shift to turn H2 + CO2 into CO based syngas and make liquid fuels depending on the catalysts you can make any of the simple alcohols like methanol, ethanol, propanol, butanol. Propanol and Butanol are close enough to petrol in Mj/Kg that no adjustments are needed for modern OBDII controlled engines the fuel maps are wide enough to accommodate the fuel air mix needed for either. Using cobalt catalysts the higher alkanes are in reach all the way up to C25+ Pennzoil uses this process to make synthetic motor oils, Iron catalysts yield the light alkane series with methane, ethane, propane, butane ,hexane being the dominate products. The South Africans use stores synthesis to make liquid fuels by the millions of gallons per year they source the syngas from coal but the process doesn’t care where the CO and H2 comes from as long as the CO to H2 ratio is at least one to three. The US Navy has tested and produced jet fuel from seawater using just electricity as the energy source as seawater has 180 times the CO2 content relative to air extracting CO2 from it during the electrolysis process is a free byproduct. The US Navy plans to make jet fuel on board the carriers with excess nuke power rather than shipping jet fuel around the world in tanker ships. They already flew a drone on the synthetic jet fuel from the process a F18 is next.
Gasoline is a dangerous liquid that emits a dangerous fume.
That’s the thing about hydrogen. The cliffnotes version is that hydrogen is locked up, and it takes energy to free it.
If you use electricity to free it, the one that comes to my mind is hydrolysis. Applying electricity to two electrodes in water (of different materials if I recall) to separate the hydrogen from the oxygen. It’s sorta like a battery in reverse, which uses seperated charged materials to close a circuit to release the potential. Except a water batter would be terribly inefficient. So is the reverse. you have to apply wayy too much energy to seperate the hydrogen compared to what you get back. And where does that energy come from? You don’t pull it out of no where. Whatever is the source of the energy that you use to fuel the hydrolysis would be a lot more efficient to use directly for your energy needs