A friend of mine made one and it made enough hydrogen to make a candle size flame, it also got extremely hot very quickly, the trouble he had was the amount of electricity that it used.
A few weeks later he bought one of the commercially produced electrolysis machines that had a fuel cell of sorts, a tank of water mixed with lye, regulated power supply, pressure monitoring system and it worked a better then the mason jar, slightly more efficient and would make a slightly larger flame, about like you can with a lighter if you turn it up all the way (4" long or so) but any more and it would trip the breaker (15amp, 120 volt... 1,800 watts!!!) that is alot of power! two and a half times as much as your cars alternator is able to put out at it's peek (would wear out rather quickly putting out it's peek) so if you really want to try this kind of thing I would simply go to a welding shop and buy a tank of hydrogen, they extract it from natural gas so it's pretty cheap, and if you are only needing the amount that you could get out of one of these devices then it should last you for years.
it has alot of useful information, you may also need a device called an EFIE to regulate your O2 sensor.
A buddy and I are in the process of building six cells to install in my geo metro. I will post a gallery of pics when it is complete. I will mention we have been working on this project for nearly a year and have seen many failing designs, this one should be the great achievement.
So was it only running off the fuel cell? Or was that just assisting the gas burning engine?
It used so much electricity and put out such a small amount of hydrogen that it would have been pointless to install it on an engine, with the amount of hydrogen it produced a tank of hydrogen from a welding shop would have lasted thousands of miles.
Come to think of it, I don't like that design, alligator clips are no way to make an internal cell connection. They may loosen with vibration and spark... it's like driving a timebomb. Some positive mechanical fastening method should be used.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice