Ammonia
An H2 Carrier
How do we transport hydrogen? Usually pressurized tanks are used as a solution. For a cheaper alternative researchers are looking at "hydrogen carriers", substances which contain H2, but can be carried efficiently.
Among these products ammonia stands out. Ammonia is advantageous in transportation and storage because it has large hydrogen content per unit volume, and is easily liquefiable (8.46 atm at 20°C). So existing liquid transportation methods can carry it. The formula is for ammonia NH3, hydrogen H2. Two H's as we see are in NH3.
There is already a huge infrastructure for producing ammonia. It is produced about 150 million tons per year. Ammonia is used in cleaning products, known for its sharp smell and ability to clean any kind of grease. In movies, if dude passed out, someone brings a cloth to his nose, he smell it, and wakes right the f--k up. That's ammonia.
Clean production methods: Folks at George Washington University came up with an approach that uses air and water as a source of H2 . Air is made up of 78% N2 . In their process the bubble of wet air is passed through a mixture of tiny particles of iron oxide and molten NaOH and KOH. When electricity is applied H2 is extracted from water and allows H2O and air to interact directly to form NH3.
How to use ammonia as fuel: either convert it to hydrogen as needed and use H2 fuel cells for power. Some are also looking at ammonia fuel cells to use NH3 directly in the FC. No carbon emissions in either case.
[Danish company] Haldor Topsoe has greatly improved the near-term prospects for green ammonia by announcing a demonstration of its next-generation ammonia synthesis plant. This new technology uses a solid oxide electrolysis cell to make synthesis gas (hydrogen and nitrogen), which feeds Haldor Topsoe’s existing technology: the Haber-Bosch plant. The product is ammonia, made from air, water, and renewable electricity ...
“We expect that ammonia can be used for transportation and efficient storage of energy. The greatest advantage of ammonia is that it has a high energy density which makes it an effective fuel and energy storage option – and it can thereby solve some of the most important challenges of creating a sustainable energy system of the future,” says project leader, Senior Principal Scientist John Bøgild Hansen. ...
In conventional plants today, ammonia is made by combining hydrogen, produced from coal or natural gas or another polluting fuel, with nitrogen, produced by an air separation unit (ASU). Polluting hydrocarbons aren’t the only viable source of hydrogen but, in most places, they are the cheapest. I’ve previously written about how today’s natural gas-fed Haber-Bosch plant is almost perfectly energy efficient, due to decades of incremental innovation co-optimizing the steam methane reformation (SMR) units, which produce hydrogen from natural gas, and the HB units.
Since the start of the 20th Century, however, ammonia plants around the world have used electrolyzers to produce hydrogen from water, making industrial quantities of carbon-free “green” ammonia. Due to economics, only a couple of these plants still operate today. This technology always uses alkaline electrolysis cells (AEC) to produce the hydrogen that is fed to the HB unit. AEC is a mature technology but, unlike SMR, it did not evolve alongside HB; it has not been integrated and co-optimized over decades into the design and engineering of an ammonia plant. ...
Ammonia Fuel-Cells
The project will see an offshore vessel, Viking Energy, which is owned and operated by Eidesvik and on contract to energy major Equinor, have a large 2MW ammonia fuel cell retrofitted, allowing it to sail solely on the clean fuel for up to 3,000 hours annually. As such the project will demonstrate that long-range zero-emission voyages with high power on larger ships is possible.
The low temperature [alkaline anion exchange membrane direct ammonia fuel-cell] AEM-DAFCs part in this article not only clearly reveals the ammonia oxidation mechanisms and the effects of each component on the fuel cell performance, but also provides possible future research directions from perspectives on materials design for electrode catalysts and AEMs, respectively...
AEM-DAFCs usually supply air and water vapor into cells at the cathode, and the oxygen with react with water in the air to form hydroxide ions. As the alkaline membrane employs the exchange of anions, those hydroxide ions travel to the anode side through the membrane. While the ammonia is diffused into anode side, it will react with those hydroxide ions in the anode catalyst layer to form nitrogen and water molecules.
In recent years, the development of low temperature AEM-DAFCs and high temperature SO-DAFCs have been made to address issues regarding to en ergy conversion systems. For the low temperature AEM-DAFCs, non- platinum group catalysts were developed with a low cost and higher catalytic activity for the AOR. Also, the hydroxide membrane with a high ionic conductivity and mechanical strength was demonstrated. On the other hand, improvements on the novel electrode and electrolyte materials also have been made for the high temperature SO-DAFCs, as shown in the record, the highest peak power density of 1380 mW/ cm 2 at 850 C was obtained. However, the current development for DAFCs is still in an early stage, which is far away from commercialization. As discussed earlier, the low temperature AEM-DAFCs need to address the issues on ammonia cross-over, chemical durability of membrane elec trolyte and low catalytic activity electro-catalysts
Xu et al. reported the first direct NH 3 BH 3 fuel cell based on an NaOH electrolyte, while a direct ammonia borane fuel cell based on an alkaline membrane electrolyte has also been demonstrated. A study of the use of ammonia borane as the fuel in an alkaline fuel-cell power supply achieved a power density of 315 mW cm C 2 at ambient pressure and near ambient temperature
References