Researchers at the RIKEN Center for Emergent Matter Science (CEMS) in Japan have found a simple and affordable way to store ammonia, an important chemical in a range of industries. The discovery could also help in establishing a hydrogen-based economy.

Ammonia, chemically written as NH₃, is widely used across industries ranging from textiles to pharmaceuticals and is an important component in the manufacturing of fertilisers. For its current use, ammonia is stored in pressure-resistant containers after liquefying it at temperatures of -27 Fahrenheit (-33 degrees Celsius).

Alternate methods of storing ammonia in porous compounds have been explored. The storage and retrieval process can be achieved at room temperature, but the storage capacity of these compounds is limited. 

A research team led by Masuki Kawamoto at RIKEN CEMS has now found that perovskites, crystalline structures associated with improving energy conversion efficiencies of solar panels, can also serve as an excellent medium for the storage and retrieval of ammonia.

Perovskite as an ammonia carrier

Kawamoto's team found that the perovskite ethyl ammonium lead iodide (EAPbI3) reacts with ammonia at room temperature and pressure to make lead iodide hydroxide, or Pb(OH)I. Ethyl ammonium lead iodide has a one-dimensional columnar structure but, after reacting with ammonia, forms a two-dimensional layered structure.

Ammonia is a highly corrosive gas, but the chemical reaction with the perovskite allows for its safe storage that does not need any special equipment to store it either. The retrieval process is also very straightforward. Under vacuum, ethyl ammonium lead iodide can be heated to 50 degrees Celsius to release ammonia gas. 

In comparison, ammonia stored in porous compounds needs temperatures of about 150 degrees Celsius for recovery.

Moving to a hydrogen economy

The discovery of the role of perovskite is very important since it also offers a way to store hydrogen. Each molecule of ammonia packs three atoms of hydrogen and packing 20% of the weight of the molecule.

On its own, hydrogen is highly combustible, but ammonia does not combust easily, making it a good medium to store it until needed.

The perovskite-ammonia reaction is fully reversible, and the perovskite can be reused to store ammonia again after retrieval is completed. Interestingly, the perovskite also changes colour to white when it stores ammonia and returns to its original yellow after ammonia is retrieved. Scientists can exploit this feature to make colour-based sensors to determine the amount of ammonia stored in the perovskite.

Our attempts to move away from fossil fuels are likely to prove futile if we cannot find alternatives to carry out tasks like long haul and heavy transport. Hydrogen's power density is almost thrice that of gasoline or diesel, but its combustible nature brings high risk.

A simple and affordable method where hydrogen can be extracted at the site of its need, only in amounts that it is required, will pave a quicker way towards a hydrogen-based economy in the near future.