For boats, fuel cells can make sense. But air travel not only requires a high energy density but also a high power density, and here the fuel cells are relatively weak even by car standards. The alternative is to burn hydrogen, which introduces an inefficiency that eats up most of your advantage. For a car, you can have a small auxiliary battery, but a jet engine will run at max power for several minutes continuously during take-off, and for existing jet engines the power-to-weight ratio is considered a crucial figure of merit.
For hydrogen storage, the DoE targets are truly sobering [1]. That whittles down hydrogen from roughly 100 times as dense as batteries to about 5. Throw a 50% thermodynamic efficiency (jet engines are not efficient!) on top of that and hydrogen still has an advantage, but it lags quite badly behind jet fuel. There have been four decades of intensive government-sponsored research effort into hydrogen storage materials, but all existing systems in practical use rely on fiber-composite tanks at 700 bar.
You get better results with an ammonia-burning jet engine. Here the tank weight is negligible and the hydrogen storage density is effectively 15% (after correcting for the enthalpy of formation). But ammonia still has just half the energy density of jet fuel, and it's rather unpleasant to work with. Plus, the existing production process of ammonia faces its own serious inefficiencies, and extensive investigation of more efficient ammonia production has been painstaking with only one Japanese startup [3] that is behind its timeline (probably a little COVID-influenced) and other contenders at lab stage.
With the direct ammonia fuel cell, the power density issue is even worse, but the energy density is very good. This technology competes well with fossil fuels for weight-sensitive applications that do not require high power (DARPA has been interested in a DAFC drone). But ammonia fuel cells are mostly at lab stage, partially because ammonia production remains disappointing (despite a theoretical energy cost of zero) despite considerable research effort.
1: https://www.energy.gov/eere/fuelcells/hydrogen-storage
2: https://www.google.com/search?client=firefox-b-1-lm&q=tsubam...