Safety and ease of handling...and regulatory issues related to those. Ammonia is on the EPA list of 366 extremely hazardous substances subject to community right-to-know provisions of the Superfund Act and emergency planning provisions of the Clean Air Act.

That&rsquo’s one reason researchers have concentrated on solid state forms...like these tablets, or the ammonia-borane complexes.

According to the DTU group, the tablets have the same volume density as liquid ammonia, but are more stable...so it’s easier to design a safe container for the metal ammine complex, and even if it is outside a container it is simple to handle at room temperature due to the slow kinetics.

The T-Raissi paper cited above has a good background on the past decades of looking at ammonia as a hydrogen storage compound. (The “Hydrogen Energy Economy” talk kicked off first in the early 1970s.)

Well, neither is particularly good for humans...:-)

Ammonia seems to carry more of a potential immediate hazard from inhalation. In other words, breathing in even relatively low amounts of ammonia will irritate the lungs, and in higher concentrations, lead to pulmonary edema and possibly death. Inhaling gasoline fumes in small amounts will make you dizzy. (Very large amounts could put you into a coma. Gasoline is also a potential carcinogen.)

From the point of view of a widespread fueling infrastructure—in which there are inevitably going to be spills, leakages and the occasional customer getting a good whiff—liquid ammonia would be risky.

also note that ammonia is a gas at room temp (boiling point = -33 C), so liquid ammonia I think is stored under pressure, which makes handling even more difficult. When released, it is detectable by smell at about 50 ppm, so it doesnt take much to stink a lot, and it's highly corrosive and highly toxic by inhalation. I think that adds up to a lot more dangerous than gasoline, which, with the exception of flammability, is relatively easy to work with because it's a liquid and isnt especially toxic for low exposures by skin contact or inhalation like you'd get when filling a tank.

Hydrogen - in any form - will never prove to be a practical fuel for small vehicles.

Think renewable biofuels...

It is hard to imagine ammonia ever gaining consumer acceptance as a passenger vehicle fuel because of the smell alone. In addition, most ammonia is currently manufactured from natural gas with CO2 as a byproduct which eliminates much of the purpose of using it as fuel, unless additional terawatts of wind, solar and nuclear electrical plant capacity is built to produce ammonia through some other process involving the electrolysis of water.

This may not be the solution to providing the worlds future energy needs, but it gets people thinking in the right direction. Hydrogen can be sustainably produced from water and electrical power (generated from wind, tidal, or solar energy), but hydrogen is difficult to store and transport. There are huge wind resources in the Aleutian Islands and Patagonia, but no way to get the energy to where it is needed. 5 megawatt wind turbines on a 200 mile by 10 mile area of the Aleutians (with typical spacing between turbines) would generate enough energy to replace ALL of the petroleum consumed in the U.S. for transportation (~ 12 million barrels/day). By converting H2 to ammonia, using the Haber process and N2 from air, we have an easily transportable form of the energy. We are working on a different scheme whereby the ammonia is converted into guanidine (CH5N3) which is a stable solid. When combined with water at about 100 C, ammonia is released in two steps. One molecule of CO2 is also released, but that CO2 was required in the synthesis of guanidine so the process is sustainable and CO2 neutral. This process is similar to that mentioned in one post, the process by Amendola which uses urea, only we store about 1.5 x the amount of ammonia per unit weight.

Greetings folks--

I'm really happy to see this much interest in hydrogen storage by ammonia and ammonia "cousins".

I congratulate the DTU folks on their announcement of a way to store ammonia (therefore, hydrogen) in solid form. I just feel I need to provide some clarifying/factual information. This is good work by the Danes and deserves recognition. But, as far as ammonia as a hydrogen fuel, it's just a peek at what's possible...

I barely know where to start...(probably won't take you long to determine I'm an anhydrous ammonia fan)...

1. The DTU folks have issued a press release about a solid metal (magnesium) ammmine complex (MAC) with a hydrogen content of 9.1 percent. Anhydrous ammonia--NH3 ("ammonia") is 17.6 percent hydrogen. Also, ammonia is a pumpable liquid at room temperature with a mild pressure of only 125 psi, much like propane. In fact, you can store liquid ammonia quite readily in propane tanks.

2. The solid MAC reportedly liberates ammonia gas at 347C (620K, over 650F). Anhydrous ammonia is already a gas at room temperature.

3. The solid MAC is reported as "reversible", liberating ammonia (not hydrogen) gas at 347C. (Probably using the ammonia partial pressure (not hydrogen) for the reaction driver to establish/shift reversibility). So a "filling station" for this solid product would be an ammonia pressurization station, not a hydrogen station.

4. It is reported that the heat of formation for the magnesium ammine is 40-80 kJ/mol NH3. So, of course, the reversibility comes with a 10-20% energy burden.

5. Quoting loosely from T-Raissi report quoted in the DTU paper, "... anhydrous ammonia is a a wonderful fuel, except for its toxicity..." I'M NOT SURE WHERE THIS FOLKLORE COMES FROM, BUT AS A FARMERGUY, I KNOW THAT APPROXIMATELY 15 MILLION TONS OF NH3 (ANHYDROUS AMMONIA, PURE AND SIMPLE), ARE CONSUMED IN THE US MIDWEST AS FERTILIZER ON AN ANNUAL BASIS. Don't you think that the farmers (no farmer jokes...) have figured out the risks and have developed safe transport/ storage/ transfer/ handling procedures over the last 50 or more years? Check the accident stats in Iowa, Nebraska, Kansas, you name it. Not to mention, the current existence of 2000+ miles of ammonia pipeline in the US Midwest.

As another former farm guy, the father of one of my best childhood friends nearly died from an accidental blast to the face from anhydrous ammonia while refilling tanks. He temporarily lost his sight, it peeled several layers of skin from his face and was left with permanent scarring in his throat. Not to mention that to this day he has no sense of taste or smell. Of course, this is just one event, but the point is that this isn't the sort of stuff that a soccer mom is going to want to handle directly.

Speaking of smell, ammonia stinks (alot) and even the inevitable tiny leaks will be noticeable. Nobody will want to live or have a business within a block of an anydrous filling station.

Ammonia may eventually find acceptance in cargo ships, maybe locomotives, etc. but it is hard envisioning acceptance of the stuff in passenger vehicles.