[Asia Economy Yeongnam Reporting Headquarters Reporter Hwang Du-yeol] Professor Choi Geum-su of the Department of Physics at UNIST recently revealed the theoretical principle by which carbon-based catalysts promote electrochemical reactions, reporting it in ‘ACS Nano’.
The core content of the report is that the defects and structural flexibility of carbon, combined with chemical reactions, enable catalytic activity without precious metals like platinum.
Professor Choi expressed hope that “this could provide guidelines for introducing defects into carbon-based catalysts to maximize the efficiency and durability of carbon-based catalysts that do not contain precious metals.”
Oxygen reduction reaction is necessary for hydrogen production by water electrolysis, metal-air secondary batteries, hydrogen fuel cells, and so on.
The reaction is a process where oxygen, hydrogen, and electrons meet to form water, but without a catalyst, the reaction does not proceed well, so platinum (Pt), a precious metal known for its excellent catalytic performance, was essential. However, platinum is expensive and has poor durability, so alternatives are needed.
Carbon-based catalysts are actively researched as promising alternatives, and both the efficiency and composition of the catalysts are steadily improving. However, the reason why carbon-based catalysts promote electrochemical reactions has not been clearly identified, slowing the development of carbon-based catalysts.
This study focused on the unique structural characteristics of carbon to elucidate the principle by which carbon-based catalysts activate reactions.
There are two main types of carbon structures. One is the ‘two-dimensional planar structure’ with three bonds, like graphene or graphite, and the other is the ‘tetrahedral structure’ with four bonds, like diamond.
When two-dimensional carbon forms new bonds, it transforms into a three-dimensional tetrahedral structure, which requires high energy. This high energy acts as a barrier preventing carbon from forming new bonds and leads to the low reactivity of carbon materials.
Quantum mechanics-based calculations showed that defects increase the structural flexibility of carbon, thereby lowering the energy barrier required for carbon structural transformation and enabling catalytic reactions.
Additionally, molecular dynamics calculations demonstrated that nitrogen doped into carbon materials forms a stable structure, which is advantageous in synthesis compared to carbon vacancies.
Results from quantum mechanics-based calculations showed that defects increase the structural flexibility of carbon, lowering the energy barrier required for carbon structural transformation and enabling catalytic reactions.
Moreover, molecular dynamics calculation results showed that nitrogen doped into carbon materials forms a stable structure, which is more favorable than carbon vacancies from a synthesis perspective.
Professor Choi said, “We found that not only the ‘local and static’ electronic structure characteristics mainly addressed in previous studies but also the ‘non-local and dynamic’ structural characteristics have a decisive effect on adsorption reactions,” adding, “These results can be applied not only to electrochemical catalytic reactions but also to general chemical reactions in carbon materials, providing an expanded framework for understanding adsorption reactions.”
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