My idea too.
I experiment for a few months now with a traction battery (2V but 300 amps!!) and this works fine.
I use a frequency generator, coupled to a MOSFET an try to find frequencies where water splits more easily.
250kHz is fine, 146Hz too, 21 MHz also....
The idea of using a microwave to pre-treat the water will be next, together with sending the water through a pipe in a strong bucking magnetic field before splitting it.
Strong bucking magnetic fields tend to split water without any electricity!!
take 2 magnets and press them as close as possible (bucking that is) and in between a strange thing occurs : a circel of small bubbles appears that rotates slightly. These bubbles are probably that compound gases (O2 and H2, or some other like Brown's gas).
Results will follow if I find the time to experiment.