South Korean researchers have developed a high-performance catalyst that enables more efficient upcycling of waste plastics. The team also identified the underlying reaction mechanism at the atomic level, a finding expected to advance eco-friendly resource-recycling technologies — including the conversion of waste materials into high-value chemicals.
Ajou University announced Thursday that a research team led by Professor Cho In-sun of the Department of Advanced Materials Engineering and the Graduate School of Energy Systems developed an electrochemical catalyst that converts ethylene glycol (EG) derived from waste plastics into formic acid, a high-value chemical, by introducing cobalt (Co) into a nickel-based catalyst.
The findings were published online in October in Applied Catalysis B: Environment and Energy, a leading international journal in the fields of energy, environment and catalysis, under the title "Lattice oxygen unlocked: Descriptor-guided edge doping of NiOOH for selective upcycling of ethylene glycol to formic acid."
The study was conducted by Ajou University researchers in collaboration with the Institute of Computational Chemistry and Catalysis at the University of Girona in Spain and the Korea Basic Science Institute (KBSI). Dr. Samadhan Kapse of the University of Girona and Professor Arumugam Sivanantham of Ajou University's Department of Advanced Materials Engineering served as co-first authors.
Professor Cho served as corresponding author. Kapse handled theoretical calculations to identify the catalyst's atomic structure and reaction mechanism, while Sivanantham was responsible for fabricating the catalyst and evaluating its electrochemical performance. Kim Seong-sun, a researcher at KBSI, contributed as a co-author, conducting structural and property analysis of the catalyst.
As global plastic consumption has surged, the disposal of waste plastics has emerged as a pressing environmental issue. Polyethylene terephthalate, or PET — widely used in water bottles and food packaging — is discarded in large quantities after use, making technologies that recycle it into useful resources increasingly important.
While conventional plastic recycling has largely involved shredding or melting waste plastics to produce new plastic products, upcycling — a process that chemically breaks down waste plastics and converts them into more valuable substances — has been drawing growing attention. A prime example is the conversion of ethylene glycol, obtained by breaking down PET, into formic acid, a basic chemical feedstock. Formic acid is used in chemical manufacturing and various industrial processes, and is also being studied as an energy material for storing and transporting hydrogen.
Converting used PET into useful chemical feedstocks involves two main steps. First, PET is chemically broken down in an alkaline solution to yield ethylene glycol, one of the raw materials that make up the plastic. An electrode is then placed in a solution containing ethylene glycol and electricity is supplied, triggering an electrochemical reaction at the electrode surface in which ethylene glycol is oxidized and converted into formic acid.
Compared with processes that require high-temperature and high-pressure conditions, this electrochemical conversion technology induces chemical reactions using electricity under relatively mild conditions. Using an appropriate catalyst can reduce the electrical energy needed for the reaction while efficiently producing the desired chemical. Combining this reaction with a hydrogen production process also makes it possible to simultaneously convert waste-plastic-derived materials into useful chemical feedstocks at one electrode while producing hydrogen at the other, drawing attention as an energy-efficient resource-recycling technology.
Converting ethylene glycol into formic acid is complicated, however, by multiple chemical reactions occurring simultaneously, making it difficult to selectively produce only the desired substance. Catalysts — materials that facilitate chemical reactions by lowering the energy required and steering specific reactions to occur preferentially — play a critical role here. Producing formic acid efficiently therefore requires a high-performance catalyst capable of promoting the oxidation of ethylene glycol while suppressing unwanted side reactions.
To address this challenge, the Ajou University research team introduced various metallic elements into a nickel oxyhydroxide (NiOOH)-based catalyst and analyzed the chemical reactions occurring on the catalyst surface at the atomic level. Using density functional theory (DFT) calculations, the team compared how different metallic elements affect the catalyst's reaction characteristics. The results showed that introducing cobalt caused oxygen atoms within the catalyst to participate more actively in the reaction, significantly lowering the energy barrier required to convert ethylene glycol into formic acid.
The team also found that cobalt not only participates directly in the reaction but also alters the electronic properties of neighboring oxygen atoms to promote it. This points to a new design principle: improving catalyst performance requires considering not only the metallic element itself but also the properties of adjacent oxygen atoms.
The team validated these theoretical predictions through catalyst fabrication and experimentation. The cobalt-doped nickel-based catalyst outperformed the conventional nickel catalyst, achieving approximately 2.1 times the formic acid production rate. Specifically, it produced about 0.92 mmol of formic acid per square centimeter of electrode area per hour, with a Faradaic efficiency for formic acid production of approximately 60 percent. Faradaic efficiency refers to the proportion of electrical energy used in the reaction that goes toward producing the desired substance.
The voltage required to drive the same level of electrochemical reaction was also lower than that needed for the conventional catalyst, confirming the potential to carry out the reaction with less energy. The results demonstrate that introducing cobalt can simultaneously enhance both catalytic activity and formic acid production performance.
The catalyst also retained more than 80 percent of its initial current during 10 consecutive hours of operation, with Faradaic efficiency for formic acid production remaining stable at around 60 percent. This indicates that even with extended continuous use, degradation in reaction performance is limited and the catalyst's ability to selectively produce formic acid is maintained.
The research team also evaluated the catalyst's performance using a solution obtained by chemically breaking down actual waste plastics. The catalyst achieved a Faradaic efficiency of 61.2 percent for formic acid production and maintained stable reaction performance over 10 hours. The results show that the catalyst can operate effectively not only in pure ethylene glycol solutions but also in real waste-plastic-derived solutions containing multiple decomposition byproducts, suggesting broad potential for application in waste plastic resource-recovery technologies.
"The key achievement of this research lies not simply in developing a new catalyst, but in systematically identifying — through both theory and experiment — which atoms drive the catalytic reaction and how that reactivity can be controlled," Professor Cho said.
Cho added that applying these catalyst design principles to a wider range of waste-resource conversion reactions could contribute to the development of eco-friendly resource-recycling technologies that transform waste into high-value chemicals.
The research was supported by the Ministry of Science and ICT and the National Research Foundation of Korea.
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