As highlighted in our sister publication, Trends, existing battery technology provides a poor solution for macro-scale clean energy storage. And dramatically better battery chemistries won’t be widely available for decades. Hydrogen avoids most of these problems, but we need a safe way to store and transport hydrogen. One promising alternative is to store hydrogen as part of another molecule and extract it as needed.
Ammonia, chemically written as NH3, makes an excellent hydrogen carrier because three hydrogen atoms are packed into each molecule, with almost 20% of ammonia being hydrogen by weight. It provides an efficient intermediary for turning nuclear power and solar radiation into clean liquid fuel for automobiles, ships, aircraft, and other uses. The problem, however, is that ammonia is a highly corrosive gas, making it difficult to store and use.
Currently, ammonia is generally stored by liquefying it at temperatures well below freezing in pressure-resistant containers. Porous compounds can also store ammonia at room temperature and pressure, but their storage capacity is low, and the ammonia cannot always be retrieved easily. But there may be a better way.
Researchers at the RIKEN Institute in Japan have discovered a compound that uses a chemical reaction to store ammonia. This discovery makes it possible to safely and conveniently store ammonia, as well as the hydrogen it carries. This finding could help lead the way to a practical hydrogen economy.
The new study published in Journal of the American Chemical Society, reports on the discovery of a perovskite, which can easily store ammonia and allows easy and complete retrieval at relatively low temperatures. A research team at Japan’s RIKEN CEMS focused on a perovskite called ethyl-ammonium lead iodide. They discovered that this material can safely store corrosive ammonia gas as a nitrogen compound using a process that is much cheaper than liquification in pressurized containers at -27.4°F. Even more importantly, the process to retrieve the stored ammonia is very simple.
The stored nitrogen compound undergoes a reverse reaction at 122°F under vacuum conditions and releases ammonia. Best of all, after returning to the original structure, the perovskite can be reused, allowing ammonia to be repeatedly stored and extracted, just like a car gas tank. An added bonus is that the normally yellow compound becomes white after the reaction. Therefore, color-based ammonia sensors could be used to determine the amount of ammonia stored.
The new storage method has several uses. In the short-term, the researchers have developed a safe method for storing ammonia, which already has multiple commercial uses ranging from fertilizer to pharmaceuticals to textiles. In the long-run, this simple and efficient method could be a part of the solution for achieving a decarbonized society through the use of ammonia as a carbon-free hydrogen carrier.