Aluminum + Gallium + H20 =
Possibly. What happens, is the gallium acts as a catalyst and prevents the aluminum from oxidizing and when you add water, the aluminum pulls off the oxygen from the water molecules and then the H2 can then be utilized as either a combustible or to energize a fuel cell. There are waste products involved but those consist of water (exhaust) and aluminum oxide & the gallium.
However, discharging water as exhaust is unlikely to get people worked up and the other two wastes are recyclable and can be processed & returned to the energy cycle.
Is it a wonderful development full of limitless energy? I do not know but a few concerns on my part that constrain possibilities.
How plentiful is gallium? Some quick googling leads me to believe gallium is a rare element. Will there be enough of it? How hard is it to extract from the earth?
How costly in terms of energy is recycling the aluminum oxide? There is no free lunch especially with energy. You can not drive this process by utilizing the aluminum gallium energy process we will need to utilize nuclear, coal, or some other source for that.
Very intriguing. Combine the above with fuel cells and we may finally have a practical alternative to petroleum as a fuel (however, recall petroleum is used for more than just fuel).