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Batteries are more efficient, and charge/discharge comes from same device, at a very high power rate. But $100/kwh or even $50/kwh storage cost is higher than $1/kwh cost of H2. H2 being transportable and siteable anywhere with water/electricity access, makes it much more useful than alternate storage technologies.

The battery problem is that it will be sized too big to charge or discharge on some alternate days, and too small to fully meet energy needs on others. The high storage costs mean an economic requirement to have at least/close to full daily charge/discharge cycles.

The sellable/transportable property of H2 means producing an unlimited amount in one place, and distributing it as needed. H2 has many different applications than fuel/electricity conversion as well. If we ever make too much, we can shoot stuff into space with it.

Electrolysis of Hydrogen is green if renewables power it. It is almost as automatable as battery storage. It is transportable/exportable energy that is cheaper to transport than building electric wires, even by truck. A fuel cell is a hydrogen to electricity converter that is twice as efficient in obtaining power from fuel than an ICE engine. Other than fuel, hydrogen has many critical chemical applications.

Hydrogen electrolysis is the key technology. Just make it, and figure out how to sell it later. Biden's IRA was ok for hydrogen. China is doing better as usual. Truck sized electrolysis systems makes electrolysis portable too, and could be used to chase seasonal surplus renewables. The key to 100% renewable power is having enough power every day, and so on most days have surpluses. Hydrogen is path to monetizing that surplus, in addition to displacing some energy use with backup/resilience exportable energy.

I think the designs all end up as big combined wing aircraft to give more storage. Can work, but so many new techs and challenges that no one is really investing in it....

Airport expansions like at Gatwick and Heathrow in the UK (both very contentious) should have carbon caps to encourage investment in this kind of stuff.

For aviation, LH2 is best because the tanks are very light too, and much of the fuel is used on takeoff which has a cooling effect on the remaining fuel. Cruising at matched boil off rate works well, and there should be enough pressure resilience for reserve fuel. Small battery can also help with takeoff and regen to handle aborted landings, as well as manage with boil off rate.

A technical challenge is dealing with very cold/liquid H2 in the fuel cell, and pipes. Unclear if that is worked out yet.