Researchers at the RIKEN Center for Emergent Matter Science (CEMS) in Japan have made a groundbreaking discovery regarding the storage of ammonia. They have identified a compound that utilizes a chemical reaction to store ammonia, offering a safer and more convenient method for handling this important chemical.
The findings, published in the Journal of the American Chemical Society on July 10, have significant implications for the transition from carbon-based to hydrogen-based energy systems. Storing and transporting hydrogen safely is a crucial aspect of this transition since hydrogen is highly combustible on its own. One approach is to store hydrogen as part of another molecule and release it when needed. Ammonia, with its chemical formula NH3, is a suitable carrier for hydrogen because each molecule contains three hydrogen atoms, making up nearly 20% of its weight.
However, the corrosive nature of ammonia poses challenges for storage and usage. Currently, ammonia is typically stored by liquefying it at extremely low temperatures in pressure-resistant containers. Alternatively, porous compounds can store ammonia at room temperature and pressure, but their storage capacity is limited, and ammonia retrieval is not always straightforward.
The research team, led by Masuki Kawamoto at RIKEN CEMS, focused on a perovskite compound called ethylammonium lead iodide (EAPbI3). Perovskites are materials with a distinctive repetitive crystal structure. The team discovered that the one-dimensional columnar structure of EAPbI3 undergoes a chemical reaction with ammonia at room temperature and pressure, transforming into a two-dimensional layered structure called lead iodide hydroxide (Pb(OH)I).
Through this process, ammonia is chemically converted and stored within the layered structure. As a result, EAPbI3 can safely store corrosive ammonia gas as a nitrogen compound, offering a more cost-effective alternative to liquefaction at subzero temperatures. Importantly, the retrieval process is equally simple.
Surprisingly, the stored ammonia in ethylammonium lead iodide can be easily extracted by gently heating the compound, reversing the chemical reaction. This extraction occurs at a much lower temperature of 50°C (122°F) under vacuum, compared to the 150°C (302°F) or higher required for porous compounds. Consequently, EAPbI3 proves to be an excellent medium for handling corrosive gases in a straightforward and cost-effective manner.
Moreover, after returning to its original one-dimensional columnar structure, the perovskite can be reused, enabling repeated storage and extraction of ammonia. Another advantage is the compound’s color change. Following the reaction, the typically yellow compound turns white. According to Kawamoto, this color alteration opens the possibility of developing color-based ammonia sensors to measure the amount of stored ammonia.
The new storage method has immediate applications. In the short term, the researchers have devised a safe approach for storing ammonia, which has diverse uses ranging from fertilizers to pharmaceuticals and textiles. Looking ahead, co-author Yoshihiro Ito of RIKEN CEMS envisions that this simple and efficient method can contribute to the realization of a decarbonized society by employing ammonia as a carbon-free hydrogen carrier.
This research aligns with the United Nations’ Sustainable Development Goals (SDGs) set forth in 2016, particularly Goal 7: Affordable and Clean Energy and Goal 13: Climate Action.