Comment: In the video at 2:10

The narrator says: "That means that most of the energy used to drive the piston comes from the fracturing of water into the gas."

I'm sorry, but your friend from the video just said something equivalent to making water flow uphill, or the cream in your coffee miraculously unmixing and leaping back into the carton, or a scrambled egg unscrambling itself and hatching a chicken.

It REQUIRES energy to break water into hydrogen and oxygen. The pressure of the newly formed gases might be enough to move a piston, but the energy originally came from the energy you used to break apart the water. If you are forming those gases under pressure, like in a compressed piston, it will actually require even MORE energy to perform the electrolysis. THAT increased energy input is what drives the piston, not the magical energy the narrator seems to think comes from the fracturing process itself.

In an ideal closed system the energy input exactly equals energy output. In an open system, you will ALWAYS get less energy output than the amount of energy you input.

So, sorry. You don't win a car. But keep trying. Maybe you'll eventually figure out that it's impossible, maybe not.