@hacker45 (View Post)
First off, There's too less Hydrogen in Earth's atmosphere to be used as a Hydrogen-Type Scramjet.

Second, Hydrogen cannot generate enough thrust without Oxygen, a Hydrogen-Type Scramjet would only general around 1.33e pounds of thrust. you would need 3,239 Pounds of thrust to take a F-22 Raptor into the skies.

Third, is it efficient? using Hydrogen as a way of propulsion might be resouce effective and yet maybe not worth it, since Hydrogen is the lightest of all the Elements currently known, it is also the most abundant, but only in the presence of Stars & Galaxies, plus we would need much more technology to make a highly efficient Hydrogen-Dependent Engine.

Fourth, You would have to make Hydrogen in a Liquid, but cold form (Liquid Hydrogen like rockets that sends satellites into orbit.) But without Liquid Oxygen, LH2 will not generate enough thrust to push a Jet-fighter up.

@EqualsThree (View Post)

At last, thank you for explaining all the main problematic flaws understandably which I somewhat failed to do.

@hacker45 (View Post)
You would have to extract Hydrogen from the Gas Giants, but based on current tech that is impossible.

You're aware that you electrolysis takes more energy than what you get back from combustion/energy cell process. The maximum possible output, in a perfect system where no energy is wasted(e.g. 0 gravity, 0 friction, nothing wasted) you could get out what you put in, no power to run the system. The only thing that could do that is NUCLEAR FUSION!!!