Here’s a good video on how to make your own simple hydrogen generator. This might be a great auto project for you to tinker with.
Green Power Science has made a simple DIY Hydrogen Generator. The thought was that it would be run from the alternator in your car and the Hydrogen would be pumped into the engine for combustion. I am no expert but I think the energy used to create the gas would be much greater than the energy that would be produced when burning the gas. What would be interesting though is to have a large scale hydrogen generator in your garage running from solar energy and a means of using it in your car.