I have heard this one before, and if you understand the energetics of oxidation-reduction reactions, you know why what is being sold either is total bullshit, or you're not getting the whole story.  3 articles on Water fueled engines popped up today, and only in this one do I see what they are trying to do and how they're doing it.

What they are developing is a catalyst that does the hydrolysis (splitting water into H & O), and thereafter your vehicle can use the H either in a fuel cell to generate electricity, or in an ICE or Jet engine to provde mechanical energy through combustion.

The reason energetically this doesn't fly is because the reaction 2H₂O --> 2H₂+O₂ is ENDOTHERMIC, meaning it takes energy to make it happen.  All catalysts do is speed up a reaction, they don't drive reactions forward that are endothermic.

However, IF you have a catalyst that you can add energy to by charging it up electrically first, then pass water by it or through it, H & O will come out the other side.  This is what these folks at ILU are trying to make.  It's a catalytic battery of sorts.

Why is this useful?  It resolves the storage problem of Hydrogen, instead of compressing it or liquifying it, it hangs out at room temperature together with the O atom in a molecule of water.  When you need the H to power your vehicle, the catalyst splits it off, the H is recombined with a new O atom and the energy is released to do work.

Brilliant, so where's the problem?  2 places, first is WTF is this catalytic material you can charge up, and what's the energy density of it when charged?  Sounds like it's solid state material so should be very dense by mass/volume, energy/mass ratio is unknown here.  Has to be very high because of problem #2, efficiency and loss.   You have to go through two transitions here back and forth water to H and back to water, and substantial energy is lost both times.  How much?  Dunno.

However, IN THEORY,this resolves the final problem with using H as fuel, the storage problem.  It all hinges on haw much energy can be stored in the catalytic material, and how many times it can go through charge/discharge cycles.

I do not expect this material to be produced in commercial quantity anytime too soon.

https://www.iit.edu/news/goodbye-gasoline-hello-water

Goodbye Gasoline, Hello Water

RE