Actually, Al+ is purified by smelting, which is powered by applying thermal energy to a sample. As I alluded in my comment above, you can generate the thermal e

Actually, Al+ is purified by smelting, which is powered by applying thermal energy to a sample. As I alluded in my comment above, you can generate the thermal energy by any number of modes of energy transmission (electrical, chemical, RF radiation such as concentrated solar, nuclear, etc.). The primary point of the above comment was that you need electrical energy to produce H2. That's a false statement. Al+ can generate H2 without electricity. The important point is that the energy efficiency of any cyclic energy carrier system (batteries/chemical, mechanical, intertial, etc.) is only one, albeit important, factor. Other factors include mass and volumetric energy density, motion/environmental stability, cost, and so forth. The importance of each of these factors is weighted differently based on the application (e.g. automobiles, ships, trains, aircraft, domestic use, etc.).