Japanese researchers find a simple and affordable way to store hydrogen

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 122 Fahrenheit (50 degrees Celsius) to release ammonia gas.

In comparison, ammonia stored in porous compounds needs temperatures around 302 Fahrenheit (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 percent 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 color to white when it stores ammonia and returns to its original yellow after ammonia is retrieved. Scientists can exploit this feature to make color-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 toward a hydrogen-based economy in the near future.

The research findings were published July 10 in the Journal of the American Chemical Society.

Abstract:

Toward renewable energy for global leveling, compounds that can store ammonia (NH3), a carbon-free energy carrier of hydrogen, will be of great value. Here, we report an organic–inorganic halide perovskite compound that can chemically store NH3 through dynamic structural transformation. Upon NH3 uptake, a chemical structure change occurs from a one-dimensional columnar structure to a two-dimensional layered structure by addition reaction. NH3 uptake is estimated to be 10.2 mmol g–1 at 1 bar and 25 °C. In addition, NH3 extraction can be performed by a condensation reaction at 50 °C under vacuum. X-ray diffraction analysis reveals that reversible NH3 uptake/extraction originates from a cation/anion exchange reaction. This structural transformation shows the potential to integrate efficient uptake and extraction in a hybrid perovskite compound through chemical reaction. These findings will pave the way for further exploration of dynamic, reversible, and functionally useful compounds for chemical storage of NH3.