you're getting less energy out of the hydrogen than you would have gotten from the coal. This is basically a roundabout way of burning coal less efficiently. Economically, this makes no sense at all.

One last time, folks -- (1) It takes energy to produce metals from the metal compounds in their ores (except for rare cases like gold and silver which occur as the metal); (2) Converting the metal back to a metal compound releases energy (in this case stored as H[sub]2[/sub]); (3) Metals thus serve as a means of storing energy; (4) Neither step 1 nor step 2 is particularly energy-efficient, so the two-step process loses a lot of energy; (5) The price of metals in the market is strongly dependent on the amount of metals recycled as the metal; thus using metals as fuels or battery components will drive up the price of the metal, rendering the practice uneconomical, and raising the cost of the metal for other uses as well.

This is a cute trick, not a practical solution to anything.