Toyota started this project, but seemed to kill it. They were putting the electrolysis plates onboard and just adding water and an onboard electrical source.
I’m sure that by the laws of transduction it wasn’t great, but this would solve the whole “Wait 10 years for you to install billions of dollars of stations” thing.
An onboard electrical source. That means either 1) a fuel cell, 2) a battery, 3) an engine/generator system, or 4) a Mr. Fusion reactor.
What would be the point of that?
1) have the fuel cell output power the motors directly. You still need non-Renewable energy somewhere to make fuel to power the fuel cell.
2) like #1, just have the battery power the motors. You still need external non-Renewable energy sources to charge the battery.
3) you need diesel or gasoline to run the engine. Have the generator power the motors directly.
4) Obviously this is the only practical solution.