But it's a storage mechanism with the huge downside of being available from natural gas, so with widespread use of hydrogen we be equivalent to widespread continuous pumping of huge amounts of CO2 into oceans and the atmosphere. Something which most people consider foolish[1].
The infrastructure cost is totally different. Electrolysis and immobile storage of hydrogen is very cheap.
We don't have a lot of places where for a significant portion of time when there is excess power from renewables, but we will, in the future.
Edit: To clarify: if you want to produce say 40% of your yearly energy needs from wind and solar, you have to oversize the production since there are many days they produce very little. That then means there are days when they produce more than is consumed. The excess energy could be used for electrolyzing hydrogen from water.
Note no carbon involved. Also the low efficiency doesn't matter, as the energy is "free". Low cost of energy storage method is much more important in this case.
Any other reasons than "batteries are more efficient" for downvoting?
Where did you get this idea? You have to keep liquid hydrogen extremely chilled, under extreme pressure, and it inevitably leaks out. Compare to pumped water energy storage, which is at ambient temperature and pressure and has similar efficiency to the electrolysis -> fuel-cell cycle.
Also many places don't have reservoirs and mountains for pumped storage.
I'm not a big believer in the hydrogen economy, but at least incorrect notions should be corrected ("no source of hydrogen besides natural gas to be seen").