Yes, Hydrogen as a fuel.
I believe this line of thought should be revived.
Last summer in the Minneapolis area I produced hydrogen on-board in my old Ford Van. I used Sodium Hydroxide (could also have used Potassium Hydroxide) and scrap aluminum to get an extra ~100 extra miles per tank of gas. I used a single 500mL Pyrex flask, rubber stoppers with appropriate holes, sections of glass tubing, some refrigerator ice maker tubing, a second Pyrex flask as a water scrubber unit and a one way valve designed for aquarium use to keep the engine idle vacuum,which builds up in the reactor unit, from siphoning water from the scrubber into the reactor unit. The Hydrogen I produced was fed into a vacuum port on the intake manifold. The flow chart goes like this; From the reactor unit through the one way valve to the scrubber unit. From the scrubber unit to the vacuum port on the intake manifold.
It was all very simple. A couple tblsp of caustic and a couple ounces of Aluminum would "boil" Hydrogen for nearly an hour and a half. When the pressure was sufficient it would overcome the resistance of the valve. This happens mostly on level or downhill runs. With two or more reactors the pressure will be positive most of the time.
Since this is an exothermic reaction I placed the works on a hot pad in a Rubbermaid enclosure. I didn't even blow myself up. I really believe the explosive nature of Hydrogen is greatly over rated. I vented off a lot of Hydrogen doing this. It immediately dispersed and floats away, unlike gasoline fumes.
Yes, aluminum is expensive in terms of cost and energy consumption. But, it is nevertheless produced and it is available as scrap. Also, This is somewhat messy and inconvenient for short trips, and the thing freezes in the winter. This could be overcome by doing this in my garage and using a compressor for storage.
If you're wondering, I got this idea from a book that was published in 1919 by P. Litherland Teed, The Chemistry and Manufacture of Hydrogen. During WW2 Hydrogen was produced in vast quantities for lighter-than-air craft. They didn't use petroleum fuel to produce electricity to evolve Hydrogen by electrolysis of water (this is a net loss, and is why the current proposal for a Hydrogen Economy is a farce). Instead, Teed outlined perhaps a dozen methods of producing Hydrogen. The most viable and economically feasible method uses Sodium Hydroxide and ferosilica (Yes, sand) of sufficiently high silica content. The "Silicol Process" begins on page 45 of the book and is expressed as:
2Si + 2NaOH + 3 H2O = Na2Si2O5 + 2H2
Government and the energy industries surely know this. We could be producing Hydrogen for practically nothing. Makes me wonder.