Ammonia has recently attracted significant attention as a medium that can safely store and transport hydrogen, a clean energy source, at high density. However, extracting hydrogen by decomposing ammonia requires either a high-temperature reaction or the use of ruthenium (Ru), a rare and expensive precious metal, as a catalyst.
A research team including Professor Masaaki Kitano at the Institute of Integrated Research of the Institute of Science Tokyo successfully achieved ammonia decomposition activity comparable to that of Ru catalysts at low temperatures. They accomplished this by utilizing barium silicide (BaSi2) as a framework to support nickel (Ni) or cobalt (Co) catalysts. Although using Ni and Co as catalysts for ammonia decomposition has been studied before, their operation at low temperatures was previously considered difficult. The research team focused on the unique characteristics of BaSi2. It forms covalent bonds between silicon (Si) atoms while simultaneously causing a charge transfer from barium (Ba) to Si, thereby exhibiting ionic crystal-like properties as a whole. Hypothesizing that this material could enhance ammonia decomposition activity due to its ability to donate electrons more strongly to Ni and Co, the team successfully demonstrated this principle through experiments. Furthermore, by analyzing the catalysts after the reaction using X-ray photoelectron spectroscopy, they demonstrated that high catalytic performance is achieved because an intermediate complex composed of Ba, ammonia-derived nitrogen, and Ni or Co is formed at the interface of the BaSi2.
The results of this study, which revealed that non-precious metal catalysts can operate efficiently even at low temperatures, could serve as a design guideline for future catalysts. Through advancements in hydrogen utilization technologies, this breakthrough is also expected to contribute to the realization of a carbon-neutral society.
(Article: Masanori Nakajo)
