>” You need an electrical current to split water into hydrogen and oxygen gases. Where do you get that? If you use a battery, any environmentalist worth their vegan bacon will tell you: battery technology is not clean.”
No, this isn’t the problem with using a battery to split hydrogen from water, then burning the hydrogen in an ICE. The problem is that all the energy being used to move the car is coming from the battery, none is coming from the water. You don’t get more energy from recombining hydrogen with oxygen than you get from splitting them. Nor do you so much as break even, by a long shot.
Even if you did break even, it would still be pointless to convert stored electrical energy into chemical energy when you could use it to directly power an electric motor. All you have described is the world’s most needlessly inefficient battery powered car.