There a narrow window of conditions, I am told, under which HHO gas
will draw thermal energy from its surroundings so as to permit more
energy out than it costs to separate water into the H2 and the O.  But
the amount of energy is tiny and the conditions rare.  But non-
technical people have latched onto this and have high hopes that they
can run a car on it.  Not likely.

When the Indy cars are all "running on water", I'll pay attention.