Nanoparticles Could Make Hydrogen Cheaper Than Gasoline
Everyone seems to have missed the point. With efficient electrolysis, you can build the entire system into the vehicle. You'd have a closed system that cracks the water and stores the H2 in a tank. The fuel cell burns the H2, creating pure water that goes back into the tank. You'd "fill up" at home (or office, or where ever) by running the electrolysis off of grid power (or however you get it), removing the need for the gas station. You could even use the power from regenerative breaking to crack the water again (assuming you could do it fast enough), meaning you wouldn't need to lug around extra batteries or ultra-capacitors.
Remember: you shouldn't think of hydrogen as a fuel, but rather as an energy storage mechanism (like a battery).