Open-ocean farmed genetically engineered saltwater algae biofuels are the most likely long term solution. Petroleum originally comes from saltwater algae. We can grow all our own petroleum using less than 2% of the ocean surface. The land, water, and sunshine are free. The growing process creates a CO2 closed loop. The main danger is how to kill the superalgae if it starts growing uncontrollably. We could end up with the entire ocean covered with 20 feet of algae oil.
Hydrogen energy density is too low to be practical as a transportation fuel. And hydrogen spills go up into the atmosphere.
That Honda has a rated 280 miles on 4.1 kilos of hydrogen. That's better than gasoline. Even if the density is lower, the efficiency of the system is far higher. The average gasoline engine wastes over 70% of the energy contained in the gasoline.