synthetic pathway biotransformation. Carbohydrates provide high hydrogen storage densities as a liquid with mild pressurization and cryogenic constraints: It can also be stored as a solid powder. Carbohydrates are the most abundant renewable bioresource in the world. Polysaccharides (C6H10O5)n undergo a hydrolysis reaction of C6H10O5 + 7H2O → 12H2 +6CO2. As a result, hydrogen storage density in polysaccharides is 14.8 mass%. Carbohydrates are much less costly than other carriers. Hydrogen generation from carbohydrates can be implemented at mild conditions of 30~80 °C and about 1 atm, the process does not need any costly high pressure reactor, and high purity hydrogen mixed with is generated, making extra product purification unnecessary. Under the mild reaction conditions, separation of gaseous products and aqueous reaction is easy and nearly no cost. Moreover, renewable carbohydrates are non-flammable and not toxic at all. Compared to other hydrogen carriers, carbohydrates are very appealing due to their low cost, renewable source, high purity hydrogen generated, and so on. Ammonia and related compounds Ammonia Ammonia (NH3) releases H2 in an appropriate catalytic reformer. Ammonia provides high hydrogen storage densities as a liquid with mild pressurization and cryogenic constraints: It can also be stored as a liquid at room temperature and pressure when mixed with water. Ammonia is the second most commonly produced chemical in the world and a large infrastructure for making, transporting, and distributing ammonia exists. Ammonia can be reformed to produce hydrogen with no harmful waste, or can mix with existing fuels and under the right conditions burn efficiently. Since there is no carbon in ammonia, no carbon by-products are produced; thereby making this possibility a "carbon neutral" option for the future. Pure ammonia burns poorly at the atmospheric pressures found in natural gas fired water heaters and stoves. Under compression in an automobile engine it is a suitable fuel for slightly modified gasoline engines. Ammonia is a suitable alternative fuel because it has 18.6 MJ/kg energy density at NTP and carbon-free combustion byproducts. Ammonia has several challenges to widespread adaption as a hydrogen storage material. Ammonia is a toxic gas with a potent odor at standard temperature and pressure. Additionally, advances in the efficiency and scalability of ammonia decomposition are needed for commercial viability, as fuel cell membranes are highly sensitive to residual ammonia and current decomposition techniques have low yield rates. A variety of transition metals can be used to catalyze the ammonia decomposition reaction,