(From top left) Ji-heon Park (first author), Ian Jo (first author), Ho-tae Jeon (first author), Won-gyu Lee, professor of materials engineering at Hongik University (corresponding author ), In-soo Kim, Senior Researcher at KIST (corresponding author) and Bong-geun Song Professor, Department of Chemical Engineering, Hongik University (corresponding author)
Recently, with the emergence of the problem of carbon emissions due to air pollution, interest in environmentally friendly energy production methods is growing. In particular, hydrogen fuel is attracting attention as an ideal clean energy source because it can produce greater chemical energy than fossil fuels without generating carbon dioxide when burned. Hydrogen fuel is divided into gray hydrogen, blue hydrogen and green hydrogen depending on the production method. Unlike grey/blue hydrogen, which is based on fossil fuels and has the limitation of producing carbon dioxide as a by-product, green hydrogen uses water electrolysis technology which electrochemically decomposes water molecules into oxygen and hydrogen, therefore aims to become a hydrogen energy system. It can be said to be the energy production method par excellence. At this time, the development of electrochemical catalytic/electrode materials to reduce the power required for water electrolysis can be regarded as a domestic key technology for mass production of water electrolysis. However, since reserves on Earth are small and expensive platinum-based catalysts still account for the majority of them, research is underway on developing highly stable and reliable electrochemical catalysts that can replace them.
(From top) Schematic diagram of the production process of WS2-based multilayer catalyst, catalyst structure and component distribution photographed by transmission electron microscopy (TEM), and comparison table of water electrolysis performance with existing catalysts based on WS2.
The research team formed by Professor Won-gyu Lee of Hongik University (Department of Materials Science and Engineering), Professor Song Bong-geun (Department of Chemical Engineering) and senior researcher Insoo Kim of the Korea Institute of Science and Technology (KIST) is leading a research team to produce platinum through the surface restructuring of tungsten disulfide (WS2), recently in the spotlight as a low-dimensional semiconductor material. We have focused on developing next-generation catalysts that can achieve the above efficiency and stability of water electrolysis. The research team sequentially exposed peeled and mechanically transferred multilayer WS2 to argon (Ar) and oxygen (O2) plasma to form nanodomains with extreme electrochemical activity and reactivity on the surface of the material. The research team experimentally observed that the surface structure of the existing WS2 was restructured into an aggregate of partially amorphous nanodomains through various analysis techniques such as X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy and electron microscopy to transmission. Through the evaluation of electrochemical properties, the research team demonstrated that the collective composite nanostructures formed through plasma surface treatment can sustain ultra-high efficiency water electrolysis in the ultra-low voltage range for a long time. The research team also managed to calculate the experimentally observed electrochemical reactivity of individual domains and its increase in activity at the atomic level through density functional theory, and was able to theoretically demonstrate the previously experimentally observed catalytic reactivity.
(From left) Theoretical model of the nanodomains formed on the WS2 surface, calculation of the hydrogen adsorption free energy, and theoretical exchange current density for each reaction site on the domain.
Professor Won-gyu Lee, the principal investigator, said: “This study is significant as it presented a methodology to synthesize extremely efficient electrochemical catalysts in a large area through simple plasma processing. In general, plasma treatment is a surface process widely used in semiconductor processes, such as removing impurities from the surface or etching. However, this study is new as it repurposes the plasma process as a method of material structure synthesis to form new nanostructures using the structure of existing materials as a framework,” he said. He also stated: “Materials engineering is a discipline that deals with the relationship between the structure, properties and processes of materials. In carrying out this research, many relationships between structure and properties remain that have not yet been understood within the material formed through a very simple process. In particular, we are confident that selective amorphization and disorder control of low-dimensional semiconductor structures will be key to designing catalytic materials for water electrolysis and next-generation fuel cells. He also expressed his opinion on future research directions, stating: “It is essential to establish a theoretical and experimental methodology capable of systematically analyzing the structure of amorphous materials.”
The study was published as an online press release in the international academic journal Advanced Materials on the 21st of last month, and Hongik University master’s student Ji-heon Park from the Department of Materials Science and Engineering and doctoral student Ian Jo from the Department of Chimica Engineering and master’s student Ho-tae Jeon from the Department of New Materials Engineering participated as co-authors. The study was carried out with the support of the university’s Academic Research Promotion Grant and the National Research Foundation of Korea’s Outstanding Youth Research Project.
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