Could a rocket use chemical absorption of oxygen and hydrogen into some other chemical to provide storable non-cryogenic fuel for an engine with the attractive 450-to-528-second specific impulse of LH₂/LOx engines?
Obviously if you allow water the answer is “yes”, but then an unattractively large amount of energy is taken up in “releasing” your “fuel” from its “storage”. Like, several times more than your engine yields. This might be okay under some circumstances but probably not the ones where people want to use chemical rockets, like escaping a gravity well.
The problem with other forms of fuel storage is that they leave storage mass behind that is comparable to the mass of the fuel itself, which is a nonstarter when you need ratios like 100:1 just to hit orbit.
Maybe, though, you could grind up this “ash” and either dump it out or, especially early in the process when you want more thrust and less velocity, mix it into the reaction mass. I don’t think that saves the idea.