Hydrous hydrazine as a superior alternative to high-pressure gaseous hydrogen storage fuel for current PEM fuel cell powered applications.
Hydrazine is not frequently mentioned in low carbon energy circles. Despite this, hydrazine holds the title as being the only liquid hydrogen carrier that does not contain carbon atoms.
Hydrazine, being a liquid at room temperature, allows for safe and easy transport, storage and dispensing. Hydrazine is always mixed with water, between 29%-64% hydrazine by weight in water, as anhydrous hydrazine is highly unstable. Ordinary plastic containers are used to transport hydrous hydrazine, conventional tanker trucks can be used and existing fuel station infrastructure can be utilized with modifications limited to the fueling nozzles.
Hydrazine can be produced from hydrogen peroxide using a new and improved process invented in the 1970s. The feedstock required is hydrogen peroxide and ammonia. 2.4 mols of ammonia plus 1.4 mol of hydrogen peroxide react with a hydrocarbon, methyl ether ketone, to eventually synthesize into one mol of hydrazine, generating 2 mols of water. The ketone is recycled and not consumed in the process. The cost of producing hydrogen peroxide from the anthraquinone process is $227/ton for a 100% solution for raw materials and energy input.
The raw material costs for producing hydrazine hydrate excluding the original hydrogen feedstock for ammonia through the peroxide process is approximately
$6.66/kg of H2 based on current market prices assuming a price of $1.5/kg for hydrogen for the manufacturing of the hydrogen peroxide, this is roughly the cost of producing hydrogen from steam methane reforming which supplies most FCEVs today supplied with 350-700 bar technology. The cost of $6.66 is the cost above and beyond the hydrogen feedstock, as it is to be compared to the cost of transporting, compressing and dispensing hydrogen. The capital costs of the plant depend greatly on the production volumes, of which currently is very low due to the small demand for hydrazine. In ammonia synthesis, for example, 90% of the cost is the hydrogen feedstock, with the balance being the cost of the plant. Hydrazine production requires no compression and minimal temperature, conditions are very mild, 10 bar and 150 C.
Hydrazine is a very dense hydrogen carrier, containing 12.6% wt hydrogen. In a hydrous solution, it is up to 8%. Below 40% concentration in water, hydrazine vapors are not flammable. The volumetric density of hydrous hydrogen is up to 84 kg/m3, 4x higher than 700 bar storage.
Hydrazine for fuel cells.
Current PEM fuel cell technology can be used with hydrazine supplied hydrogen. With the proper catalyst, preferably bimetallic rhodium and nickel at 4:1 ratios Ni/Rh, hydrous hydrazine readily decomposes into pure hydrogen and nitrogen at room temperature. The mixture can then be fed directly into the PEM fuel cell.
Hydrous hydrazine has a comparable risk profile to methanol, with flammability risk being much lower than its toxicity risk. Hydrazine has not been shown to be carcingeic. Below 40% solution in water, it has no flash point, meaning it can not be ignited, eliminating all safety concerns that hydrogen faces due to its tremendous flammability.
In summary, hydrazine is safer than gaseous hydrogen owing to its low flammability as well as liquid nature, which minimizes the probability of direct contact.
In summary, hydrazine offers the ability to develop a safe liquid “hydrogen economy” bypassing all the safety and infrastructure issues faced by current high-pressure gas storage technology.
“Don’t try to store hydrogen by compression or liquefaction, I’ve said it and will say it again, chemistry is your friend! A few chemical reactions and some rearranging of atoms can do wonders”
Advanced Energy Systems 