Toyota Owners are being asked about new engine possibilities

Screw this gas/electric, gas/diesel stuff. That's just 2 engines/ motors to take care of. Why not just burn hydrogen just like gas. It has way less emissions and it exceeds the performance of gas. The stuff is used in rocket fuel! You could but water in your tank then convert it to hydrogen and oxygen.

 

Inefficient. Takes more energy to produce hydrogen than you get out of it.

True

It is not the most powerful rocket fuel, and was not used on the Saturn-V. It is used on modern rockets because it is cleaner, but it is still used in combination with solid rocket boosters.

No you can't. Not efficiently.
You are describing perpetual motion....
Water in tank > Separate to hydrogen > power engine > recover exhaust > condense back into water.

Problem is, the math doesn't work out that way. In reality, it is more like:
Water in tank + 10x energy > Separate to hydrogen > power engine -1x energy > recover exhaust > condense back into water.

You could do what you wrote with a big enough on-board battery, but you would effectively be running an electric vehicle because the engine could not produce enough power to move the vehicle AND recharge the batteries that would power the hydrogen generator.
You would have to recharge the battery when you got home... it would be basically a hydrogen hybrid.

 

I really wasn't saying it had to be onboard. Hydrogen stations would do this and you would just pump hydrogen in the car. BMW has a concept named hyrdrogen 7 with a v12 hydrogen engine. I think they have like 100 test models so far and have a video of it filling up with hydrogen at a station.