[Courtesy of UNIST]
Graphene is a crystalline allotrope of carbon with two-dimensional properties. The single, thin layer of graphite is a transparent and flexible conductor that holds great promise for various material and device applications, including solar cells, light-emitting diodes, touch panels and smart windows or phones. Graphene can be chemically processed into various forms.
The Ulsan National Institute of Science and Technology (UNIST) said its research team led by Jang Ji-hyun, a professor of energy and chemical engineering, used a CuFeO2 catalyst, which can selectively remove oxygen, to eliminated carbon and reduce carbon emissions. CuFeO2 is a copper iron oxide mineral known for its wide range of electrical properties.
"We introduced the first technology that transforms graphene oxide into high-quality graphene at relatively low temperatures with a carbon dioxide conversion catalyst," Jang said in a statement released by UNIST. "If commercialized, it is highly valuable as a technology that can produce high-quality graphene, a high-value material, at a low price and in large quantities."
In a typical oxidized graphene reduction process, carbon dioxide (CO2) is produced together, resulting in an empty space where carbon has been torn off, leading to reduced electrical conductivity. On the other hand, the catalyst used by Jang's team not only selectively removed oxygen but also restored the structure of graphene damaged by oxygen, the institute said.
"Our experimental data and density functional theory calculations proved that reduction which occurred on the CuFeO2 surface preferentially removed adsorbed oxygen atoms in graphene oxide sheets, leaving dissociated carbon structures to be restored to a near-perfect few-layer graphene sheet," Jang's team said in a research paper published on the website of ACS Nano, a peer-reviewed scientific journal.
By utilizing a Fischer-Tropsch reaction catalyst, the team used an in situ deoxidation and graphitization mechanism. With graphene oxide reduced on the catalyst surface under the hydrogen-poor condition, deoxidation with much-suppressed carbon loss was possible, resulting in high-quality graphene sheets.
Graphene oxide with catalysts released 92.8 percent less carbon-containing gases than graphene oxide without catalysts during the reduction process that suppressed carbon loss in graphene oxide sheets, leading to near-perfect graphene, the team said, adding that the amount of oxygen related to the epoxide group in the basal plane of graphene oxide significantly decreased to near zero in catalyst-assisted reduced graphene oxide.
The team said that catalyst-assisted reduced graphene oxide coated paper connected to a coin-cell battery successfully lit an LED bulb and acted as an efficient catalyst for hydrogen evolution and oxygen evolution reactions.
The demand for graphene is growing in the fields of semiconductors, electronics, electric batteries and composites. In May 2020, the state-run Korea Research Institute of Chemical Technology (KRICT) opened the way for the mass-production of high-quality industrial graphene in powder form without treating graphite as a strong acid.
In March 2021, South Korea's top steel group POSCO tied up with research groups and Graphene Square, a high-tech startup, to create a graphene ecosystem. Graphene Square is developing systems for the mass production of large-scale graphene synthesized by chemical vapor deposition (CVD), an effective way to produce high-quality graphene on a fairly large scale.
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