High temperature steam electrolysis

It is said to be more efficient than at lower temperatures.  If a kilogram of hydrogen can be produced for 225 megajoules, and a gallon of gasoline ( which is equivalent to about a kilogram of hydrogen in terms of energy ) yields about 126 megajoules.

Obviously, you lose something in the conversion.  Thus, you lose about 100 megajoules this way.  To produce gasoline from the hydrogen thus obtained would not be very efficient at all.

The thought I had was not to make carbon based fuels, but ammonia instead.  You might even do some cogeneration in order to make the energy conversions more efficient.  Ammonia could be made this way, and can be used as a hydrogen carrier to boot.

One objection to fuel cells as a power source, in comparison with batteries, was the relatively lower efficiency rate.  One reason for this was the necessity for compression or liquifaction of the hydrogen.   To do this requires a lot of energy, and these losses degrades efficiency, thereby adding to the problem.   Fuel cells are still more efficient than gasoline powered ICE engines.

To beat batteries, I suggest making ammonia, and then cracking it on an as-needed basis.  The ammonia will be the hydrogen carrier, thus alleviating the necessity to achieve cryogenic temperatures, and high pressures.  Ammonia crackers can possibly be put on a car, and the weight penalty might not be too bad.  Less than that of batteries, I suspect.  Batteries add a tremendous weight penalty.

Now, can we get the hydrogen source from a means that would increase efficiency so that the cost of operating a fuel cell car may be comparable to a gasoline powered ICE vehicle?  Perhaps not, but it might not matter if the energy source is cheaper.

Let's go back to the production of hydrogen seen earlier.  If it was to be produced with a molten-salt reactor, which is cheaper than coal to begin with, and if it utilized steam electrolysis to produce the the hydrogen and then ammonia, it would have to get back that 100 megajoules mentioned above in order to compete on efficiency.  But, you could do that ( on the basis of price ) if the energy source is cheaper, as is the case with molten-salt reactors.  With a higher efficiency than ICE engines, a fuel cell power source would get back more, if not all, of that efficiency penalty, and the rest could be made up by the lower price of the molten-salt reactor derived energy.

In the end, could it be cheaper than gasoline if you were to use this method?  I think that it may be possible.  Better than batteries?  Maybe not in terms of efficiency, but once again, molten-salt reactor tech wins on price.


Update:

After digging in a little deeper, I found something that may throw a money wrench into this idea.  If it takes 389 kilojoules of energy to break just one of the nh3 bonds, then that's the monkey wrench.  In other words, the idea of using ammonia as a hydrogen carrier may be flawed.  Too inefficient.

I'm gobsmacked.