It looks like AlGalCo makes an aluminum-gallium alloy that produces hydrogen + aluminum oxide when mixed with water. This seems like it would be useless in space, because the oxygen is locked away until you run the waste through an aluminum smelter.

Hmm, I wasn't thinking of re-usability for the aluminum. Just that it would keep the propellants in a safe state. water+alloy might be better than nasty toxic fluid + pressurized oxidizer. I am also not a rocket scientist.

It isn’t a question of reusable type - you need to have fuel and oxidizer to burn things. A truck can use atmospheric oxygen for the oxidizer; a rocket can’t.

I also imagine that the extra weight of the aluminum pucks would tank your Isp (though I suppose you might be able to make back some tank weight).

I willfully? missed that the O in the water binds to the Al so is unavailable for combustion (it has to, otherwise what gets consumed?).

Oh, another take, it is a molecular pump that removes oxygen from the environment and turns it into water, via burning.