Nope, not just hydrogen-Good old water-

Ive seen an almost stock harley motor be converted to run on straight water-With an efficiency that scares the oil companies. There are reasons some of these things cant be brought straight to market.

Ill give you some hints though-Think water, bronze, hydrogen peroxide, electrolysis, semipermeable electromagnetic membranes...

If you can put those parts together in the right enviroment, AMAZING things can happen