If people are still looking for a valid reason rather than blindly believing what is reported in the so called "NEWS channels", here are few facts.
Firstly, work is said to be done (in a friction-less perfect system) when there is a difference between positive difference between "Heat source" and "Heat Sink". Now electrolysis of water and combustion of H2 both produces 282.1 kJ* (286 kJ/mol: energy per mole of the combustible material ) and there is no diff between the source and the sink hence energy flow is
IMPOSSIBLE . This was proven through Thermodynamics.
[Source:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html]
Secondly, now by physics, 1.5 liter = 1500 ml or 1500 gm of water. So, 1.5 liter = 83.33 mole of water (1 mole = 18gm of water). So its electrolysis should yield 83.33 mole of H2. And from above point the electrolysis of that much water should take 23,509.16 kJ or 6.53 kwatt-hours of energy. I am not sure that a humble car battery has that kind of power rating. Moreover the man himself says that the car has not be altered in any aspect so a high energy dense battery can be stricken from discussion.
Also that much amount of hydrogen would require 1868.972 L at STP and I donn think a car tyre can provide a oxygen-free environment to store that hydrogen (as shown in the video). Hydrogen is highly explosive at 4 - 74% concentration.
Plus I recall him saying he used distilled water. As far as I know pure water is not a good conductor of electricity, (and I can say that with complete confidence, as I have tried doing it at home 20yrs back. I had to add common salt) . Commercial electrolysis generally uses 25% potassium hydroxide. I did not investigate cathode material, but I know that it must be inert, e.g., platinum,but it is not require over an high-voltage. Another consideration is that one would probably need a fairly large surface area for the cathode in order to generate the hydrogen in a reasonable amount of time.