What is Ammonia?
Ammonia is a simple compound consisting of three hydrogen atoms bonded to a single nitrogen atom and has the chemical formula NH3.  It has a boiling point of −33.34 °C (−28.012 °F) at atmospheric pressure and is normally stored as a liquefied gas.  Because of its chemical structure, it contains more hydrogen per unit volume than liquefied hydrogen.  The hydrogen is tightly bound to the nitrogen, which makes it a very stable and difficult to ignite chemical.

For more information see:
Wikipedia: Ammonia
Encyclopædia Britannica: Ammonia
NH3 Fuel Association: Introduction to NH3 Fuel