Storing hydrogen in general isn't very difficult. The problem is in storing enough hydrogen that having it react with air in a fuel cell can power something meaningful.
For example, the Hyundai Nexo has a range of 611 km (380 mi), which requires it to store 6.3 kg of hydrogen. At atmospheric temperature and pressure hydrogen has a density of 0.08988 g/L, so that would require a tank with a volume of 70 m3. For reference, a semi-trailer has a volume of about 100 m3.
> Storing hydrogen in general isn't very difficult.
That's not accurate, storing hydrogen is very difficult. The atoms are so small that they pass into the molecular matrix of storage containers, sometimes even when kept at extreme temperatures and pressures, causing "hydrogen embrittlement", which eventually destroys the container and releases all of the hydrogen.
The only truly reliable way to store hydrogen over appreciable time frames is when it's bound in molecular forms, like fossil fuels or ammonia.
hydrogen embrittlement is only really an issue if the container regularly changes temperature and the metel has to expand and or contract.
granted this is most real world scenarios. but not always.