A couple years ago an Israeli company was working on zinc or magnesium "fuel" systems for motor vehicles. The additional weight would be like an additional person in the vehicle -- not a biggie. The real problem was it would require an infrastructure, governmental action, etc. to be practical for road transportation.
I posted that it would be easier to prototype the system with something that never went very far and always returned to a home base where the oxides could be collected and sent for reprocessing.
After it's demonstrated then it could be pushed for motor vehicles.
Bret Cahill