From top left: Professor Hyunjung Kim of Sogang University, Senior Researcher Deokhwang Kwon of the Korea Institute of Science and Technology (KIST), and Principal Researcher Hoil Ji. From bottom left: Dr. Sungwook Choi of Sogang University and Dr. Younghwan Lim of KAIST. Provided by the National Research Foundation of Korea.
It has been confirmed that ruthenium atoms, which serve as a noble-metal catalyst, use defects inside a crystal as migration pathways to form catalytic particles on the surface. This finding is expected to help manufacture noble-metal catalysts that are more economical and stable than existing ones.
The National Research Foundation of Korea announced on the 2nd that a research team led by Professor Hyunjung Kim in the Department of Physics at Sogang University, in collaboration with teams led by Principal Researcher Hoil Ji and Senior Researcher Deokhwang Kwon at the Korea Institute of Science and Technology (KIST), has clarified that a physical defect known as a “dislocation” occurring inside a crystal directly carries ruthenium metal atoms and transports them to the surface.
For environmentally friendly production of fuel cells or hydrogen, noble-metal catalysts such as platinum and ruthenium are essential, but these catalysts are expensive and have limited durability.
To overcome the limitations of noble-metal catalysts, growing attention has been paid to “exsolution” technology, a phenomenon in which metal atoms spontaneously emerge from inside an oxide crystal to the surface, become anchored, and form nano-sized catalytic particles. How the exsolution phenomenon proceeds in ruthenium, however, has remained largely unknown.
To determine how ruthenium atoms pass through an oxide crystal and migrate to the surface, the research team observed perovskite oxide particles doped with ruthenium using “Bragg coherent diffraction imaging (BCDI)” and “transmission electron microscopy (TEM).”
The observations revealed that, before ruthenium atoms emerge at the surface, dislocation defects form inside the crystal. The ruthenium atoms migrate along these defects and grow toward the surface. Notably, about 75% of the ruthenium catalytic particles were formed at the ends of “mixed dislocations,” where two types of dislocations coexist. In other words, mixed dislocations act as carriers that transport ruthenium atoms.
Professor Kim said, “We have confirmed that the size and distribution of catalytic particles can be precisely engineered depending on which defects are created,” adding, “This achievement will contribute to establishing an ammonia-based hydrogen energy value chain and to the development of highly durable catalysts.” The research results were published on May 25 in the international journal Nature Communications.
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