High Temperature fission + hydrogen
Well said, Mark Halper! You are right of course that (1) it is more energy efficient to use the hydrogen directly as fuel rather than as a feedstock for gasoline ("petrol") or methanol [although most cars today run on gasoline, not hydrogen, but if price-competitive hydrogen were available this problem is solvable with existing and cost-effective technology]; and (2) doing the electrolysis to produce hydrogen can be MUCH more energy-efficient at high temperature. The experts at US national labs (such as Argonne and Idaho National Lab) have demonstrated that at 800 to 900 Celsius, you end up putting not only the electrical energy but also some of the thermal energy directly into the bond-splitting process that produces hydrogen + oxygen from water. So, yeah: a high-temperature helium-cooled fission reactor COULD make fuels from water cost-effectively. One guy at Idaho National Labs has even written papers showing how to do it with reactor temperatures as low as 600 Celsius (still too hot for a water-cooled reactor, but easily within reach of the historically-operated gas cooled reactor temperatures in Germany and Colorado.) Yes, if we were serious about getting the USA off of our petroleum dependence, we could have begun making very serious, cost-effective strides in that direction about 15 years ago. But we haven't yet, because we are currently more afraid of nuclear power than we are of Middle Eastern Wars or Climate Change... China and India will probably have to lead the way for us.