It all depends on your objective to reach with your H2 driven 747.
If your objective is to enlarge your payload (if tanks could be made lighter than 80 tons then go ahead.
If you want to reduce carbon foot print:
As long as we do not have a global surplus of green produced electricity, we do not have to bother to produce H2 by grey or black produced Electricity.
Electrolysis , cooling, pressurization, and (road) transport to the airfield costs about 5 times the amount of hydro carbons to produce of same amount of electricity for land use.
So unless the H2 would produce trust 5 times more efficient than a hydro carbon (jet) engine your carbon foot print only increases.
Only the argument that could change this is that a jet engine delivers the CO2 directly high in the atmosphere and an electrical power plant low at the ground could extract the CO2 and inject into empty gas fields.