Variations on the "modern" systems were quite popular back in the 70's, and you could buy the plans from many different sources advertising in areas such as the back of popular science and popular mechanics. I did a science fair project on this subject in high school back around 1975 where I explained the laws of thermodynamics and why a system like this doesn't work. Look into the efficiency of electrolysis processes, and how much energy is produced from burning hydrogen, no matter how you combine it with other fuels and it will all be clear to you.
Now, for the ultimate system, use wet cell batteries, capture the hydrogen and oxygen gases produces by the electrolysis that takes place in the battery and you will have the ultimate energy source. Alternator produces electricity to charge the battery and it produces hydrogen which can run the engine. With the proper marketing, and the proper amount of conspiracy hype as to why this technology is being suppressed and I could make a fortune.