The browns gas thing (usually "using water as fuel" by splitting it... Using power from the engine) actually has insanely specific be credible use case.

It turns out that in very specific engine types, you can gain additional engine efficiency that's worth the energy it took to generate the gas. The us army did a whole proper study. That net gain was, however, only present in vehicles not maintained on the usual schedule. So it did infact help some engine types that were not well maintained.

I know this because I did a dive years back. Effeciency be damned, building a reserve of browns gas that I could dump in when I wanted for a power boost sounded fun as hell to me. You wouldn't gain any effeciency (probably loose a ton) but you would have more power when you were mixing in the reserve you'd built up. I wound up not doing it because 1) the vehicle I had in mind was carb not fuel injection so no power gains there. And 2) dealing with generating, pressurizing, storing and delivering a gas isnt a ton of fun in a "for the lolz" project.