this is an absolute idiotic idea.
i electrolyse water in lessons and find that if you get the right proportion of hydrogen and oxygen within a small party balloon it will create a HUGE explosion with the slightest spark. It has been known to render people deaf.
In a vehicle , the risks are mad. If youve an arcing electric connection or dodgy HT leads you could create an underbonnet explosion. If you had an accident, say goodbye to you - your passengers and the vehicle your in collision with.
ive a video from bmw education showing a huge fuel cell in the back of a 7 series, this works fine because it is in a controlled environment, closed and not home made.
If youve ever seen an exploding car battery it is due to the same gas mixing in the correct proportion with oxygen in conjunction with a spark.