First of all, you never want hydrogen gas and oxygen together... not in a tank, not in the hose... keep them apart until you need to combine them for the purposes of burning or running a fuel cell... which separates them by a membrane anyway.
I have, however, always thought that a system for adding hydrogen to an ICE can be a good way of bridging the gap and extending the capabilities of current vehicles.
it has been done, but it does not involve making the hydrogen in the vehicle. The hydrogen would be produced from electricity, which, presumably you could generate with solar cells or wind energy do assure you have a clean energy source.
It's pretty simple:
You have a regular car which runs on gasoline, but also have a hydrogen tank onboard, possibly a metal-hydrate storage cell, as those are more compact, although currently somewhat expensive and not mainstream.
When you are home you hook your car up to tanks in your garage, which provide the hydrogen, presumably having been accumulated from a hydrogen generator that's run on a clean energy source.
When you drive to work or the store, the car starts off on gasoline. When the hydrate tank warms up (to release the h2 gas) the engine starts to take in hydrogen. It runs on anywhere from 1/3 to 2/3 hydrogen to gasoline in terms of energy from fuel. The gasoline assures the engine remains happy and lubricated and that the valves and injectors are happy.
You end up using a real lot less gasoline and the car produces less emissions. Going on a long trip? No problem. If you can't get there on a single H2 tank or if you do more driving in a day than your H2 production rate will allow, you can run the car on 100% gasoline.
Since you can get gasoline anywhere, you car can fill up at any station, but it won't get the gas millage you would if most of the power was coming from hydrogen.
You can convert your existing car too with minimal modifications.
Unfortionately, I don't believe anyone makes a complete bolt-in kit. However, a few inventive types have rigged such a system up.