The 'Hydrogen Economy' has been attracting much interest in recent times, as the price of oil continues to rise and concerns about CO2 emissions reach near hysterical levels. The major drawback of hydrogen as a fuel is one of energy density- the sheer quantity of hydrogen required to supply enough power to run, say, a car. This coupled with the inherent difficulties in storing free H2 (Being such a small molecule it is not readily constrained by the walls of a gas canister, nor is it practical to compress to a liquid except by cryogenic cooling), has led to various attempts to develop metal hydrides as storage mediums. In the case of transition metal hydrides, I rather doubt that they can ever hope to attain the 6 wt% target deemed necessary for commercial viability.(http://www.eere.energy.gov/hydrogenandfuelcells/storage/metal_hydrides.html) Lighter metals may be more promising, but in all cases the storage medium tends to be a solid.
I have amusing visions of people shovelling wheelbarrows full of this new wonder-fuel into their cars, like coal-stokers in the age of steam, but do not consider this an ideal solution.
The simplest system for hydrogen production is necessarily the one I find most appealing- I have a simple mind- and is of course the reaction of water with group I metals, the cheapest being sodium.
(This produces sodium hydroxide, converting which back into usable fuel again is a rather energy intensive process, but this particular tirade is about energy storage, not energy production).
Ideally, the fuel of choice should be a liquid, allowing it to be pumped into the car at the petrol station, and out again for reprocessing, once expended. While pumping molten sodium into one's car at 98 degrees celcius is possible, I fear the HSE would raise some objections, so the only hope is a colloidal dispersion.
Consider a fine suspension of sodium (or sodium hydride) in an inert liquid- I would suggest silicone oil, which springs to mind because it's notoriously unreactive, and I've just been having a discussion about breast implants for some reason. A surfactant would probably be needed to render the colloid stable, but something could no doubt be devised, possibly an ether of some kind.
Water would not be miscible with the resultant suspension, so hydrogen would be produced instead by mixing it with a linear alcohol, producing in the process a sodium alkoxide. I hope, for the sake of elegance, that this alkoxide would either remain dissolved in the silicone oil, or form a colloid of its own. If necessary a second surfactant could be added to the mix to facilitate this.
The sodium dispersion would be reasonably stable in air, as the individual colloid particles would be coated in a protective layer of oil, so I am now able to envisage people pulling up to the 'colloid station', having their used fuel pumped out as fresh fuel is pumped in, leaving behind a slurry of silicone and sodium alkoxides to be recycled.