With all the issue of storing hydrogen and the need for other transportation fuel options, urea is getting a few strong looks. Urea was the first natural compound synthesized. Urea is an organic compound with two HNH chains connected to a single CO molecule. That gives urea a reasonable hydrogen density in a stable and common compound.
There are a variety of uses for Urea, one of the more important is as a fertilizer. With methane or syngas as a feed stock, Urea is produced using nitrogen in the air. Since syngas can be produced through a variety of fuels including, bio-mass, coal, natural gas, petroleum and even alcohols, feed stocks are not difficult to come by. In a pinch, urea can even be produced with electrolized hydrogen and air. There is also of course natural urine from mammals.
Urea can be separated in solution into ammonia which can be used in internal combustion engines with an energy density of about half of diesel fuel. In an alkaline fuel cell, urea is more easily split into the hydrogen gas needed for our hydrogen economy.
Because of the non-hydrogen components, in the alkaline fuel cell potassium carbonate is a by produce which has uses of it own. If urea is used as a primary fuel storage medium, there would likely be an over abundance of potassium carbonate which would have to be dealt with.
With a two stage electrolysis process, converting the urea to hydrogen and potassium carbonate and then the hydrogen to energy and water, the overall efficiency would be reduced and complexity of the system would be increased. That will require more research, but there is some promise.
Another down side is urea and nitric acid can be used to make some pretty impressive explosives. Just about any energy source can be used to make a big bang, but in our terror filled world, someone will probably make and issue of the obvious.
The biggest advantage is that urea could be used in most gasoline, gas turbine and diesel engines while hydrogen fuel cell or direct ammonia fuels cell costs are brought down to more competitive levels.
Another advantage is in the production process. As a common component in fertilizer, urea, potassium carbonate and charcoal combined make an excellent soil conditioner and CO2 sequestration method. Since potassium carbonate is alkaline, it would be most useful in sandy soils that are typically acidic. An important consideration when agricultural soils tend to degrade with time. With additional hydrogen provided by high temperature electrolysis or even less efficient direct electrolysis from water, the total product chain could be profitable and beneficial.
Urea in crystalline form is not a requirement for the ammonia processes, it does though provide simple storage for easy transportation. Where pipeline infrastructure is available, ammonia would likely be a lower cost alternative. In either case, Urea and/or ammonia have serious potential as a transportation energy staple.
