Split H and O in grammar school as a science experiment using the carbon rods from a battery inserted into a beaker placed upside down in water. However, IIRC ther water had a bit of hydrochloric acid in it to catalyze the reaction. The battery was 1.5V, 2" or so in diameter and about 5" tall. We powered the thing w/ a train transformer. We were supposed to use the rods from a D Cell powered by a 6V lantern battery. Using the recommended power, you proved the presence of hydrogen by holding a match under the hydrogen test tube and you got a little flame. Using our method, we damn near burnt down the school. The nuns were not happy.
I don't know what the catalyst in the separation is in the gentleman's car. If It's HCl, Where does that residue end up?
