Can we make graphite from coal? Researchers start by finding new carbon solid
As the world’s hunger for carbon-based materials like graphite grows, Ohio University researchers this week presented evidence for a new carbon solid they dubbed “amorphous graphite.”
Physicist David Drabold and engineer Jason Trembly started with the question, “Can we make graphite from coal?”
“Graphite is an important carbon material with many applications. A fast-growing application for graphite is for battery anodes in lithium-ion batteries, and it is crucial for the electric vehicle industry – a Tesla Model S needs an average of 54 kg of graphite. Such electrodes are best if they are made of pure carbon materials, which are more difficult to obtain due to rising technological demand,” they write in their article, “Ab initio simulation of amorphous graphite,” published today in Physical Assessment Letters†
“Ab initio” means “from the beginning”, and their work follows new paths to synthetic forms of graphite from naturally occurring carbonaceous material. What they found, using different calculations, was a layered material that forms at very high temperatures (about 3000 degrees Kelvin). The layers are held together by the formation of an electron gas between the layers, but they are not the perfect layers of hexagons that make up the ideal graphene. This new material has many hexagons, but also pentagons and heptagons. That ring disorder reduces the electrical conductivity of the new material compared to graphene, but the conductivity is still high in the regions largely dominated by hexagons.
Not all hexagons
“In chemistry, the process of converting carbonaceous materials into a layered graphite structure by high temperature thermal treatment is called graphitization. In this letter, we show ab initio and machine learning molecular dynamic simulations that pure carbon networks have an overwhelming tendency to convert “towards a layered structure in a significant density and temperature window where the layering occurs even for arbitrary starting configurations. The flat layers are amorphous graphene: topologically disordered three-coordinated carbon atoms arranged in planes containing pentagons, hexagons and heptagons of carbon,” said Drabold, Distinguished Professor of Physics and Astronomy in the College of Arts and Sciences at Ohio University.
“Since this phase is topologically disordered, graphite’s usual ‘stack register’ is only respected statistically,” Drabold said. “The stratification is observed without Van der Waals corrections for functional density forces (LDA and PBE), and we discuss the formation of a delocalized electron gas in the galleries (cavities between planes) and show that cohesion between the planes is partly due to this low density electron gas. The in-plane electronic conductivity is drastically reduced compared to graphene.”
The researchers expect their announcement will lead to experiments and studies on the existence of amorphous graphite, which can be tested through exfoliation and/or experimental surface structural probes.
Trembly, Russ Professor of Mechanical Engineering and director of the Institute for Sustainable Energy and the Environment in the Russ College of Engineering and Technology at Ohio University, has worked in part on green coal applications. He and Drabold collaborated with physics PhD students Rajendra Thapa, Chinonso Ugwumadu and Kishor Nepal on the study. Drabold is also part of the Nanoscale & Quantum Phenomena Institute at OHIO, and he has published a series of papers on the theory of amorphous carbon and amorphous graphene. Drabold also highlighted the excellent work of his graduate students in conducting this research.
Surprising cohesion between the surfaces
“The question that led us to this is whether we can make graphite from coal,” Drabold said. “This paper does not fully answer that question, but it shows that carbon has an overwhelming tendency to become low, like graphite, but with many ‘defects’ such as pentagons and heptagons (five- and seven-membered rings of carbon atoms), which fit into the network very naturally. We present evidence that amorphous graphite exists, and we describe its formation process. Experiments have suggested that graphitization occurs near 3,000 K, but the details of the formation process and the nature of the disorder in the planes was unknown,” he added.
The work of the Ohio University researchers also predicts a new phase of carbon.
“Until we did this, it wasn’t at all clear that layers of amorphous graphene (the faces including pentagons and heptagons) would stick together in a layered structure. I find that quite surprising, and it’s likely that experimenters will hunt for things here.” now its existence is predicted,” Drabold said. “Carbon is the wonder element – you can make life, diamond, graphite, Bucky Balls, nanotubes, graphene, and now this. There’s a lot of interesting basic physics in there too – for example how and why the planes bind, this in itself is quite surprising to technical reasons.”
Graphene is both 3D and 2D
R. Thapa et al, Ab Initio Simulation of amorphous graphite, Physical Assessment Letters (2022). DOI: 10.1103/PhysRevLett.128.236402
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