Possible reactions at the anode and cathode. After electrodeposition, carbon nanowalls are produced on Cu(111). The mechanism of growth, with the carbon nanowalls growing from atomic steps on the Cu(111) foil.Well-ordered novel carbon nanostructures can be grown by electrodeposition from molten salts, researchers have discovered [Wang et al., Materials Today (2022), https://doi.org/10.1016/j.mattod.2022.05.018]. The team from the Institute for Basic Research (IBS) and Ulsan National Institute of Science and Technology (UNIST) synthesized regular arrangements of amorphous carbon nanowalls from a molten salt electrolyte and carbonate carbon source at 600°C on a single crystal Cu(111) foil. By varying the temperature of the molten salt and other electrochemical cell conditions, such as voltage and current, different types of carbon nanostructures can be obtained.
“We were exploring new ways of generating carbon structures,” explain Geunsik Lee, Sun Hwa Lee, and Rodney S. Ruoff, who led the work. “Electrodeposition can deposit a wide range of different types of structures depending on the experimental parameters. It helps in decomposition and recombination of carbon bonds which would not be possible by thermal effects alone at certain temperatures.”
The researchers discovered that carbon nanowalls only grow on single crystal Cu(111) foils and not on regular polycrystalline foil. The ordered patterns of curved carbon nanosheets, which grow vertically upwards from the Cu(111) surface, nucleate at slip lines – or atomic steps – on the surface of the foil, according to density functional theory calculations.
“Previously, carbon nanowalls have been synthesized by chemical vapor deposition (CVD) [and], to the best of our knowledge, all reported CVD-synthesized carbon nanowalls consisted of relatively random spatial arrangements on substrates,” say the researchers.
The scalable molten-salt electrodeposition produces different types of amorphous carbon material, including nanowalls, aligned nanofibers bundled into ribbon-like clusters, and compact nanostructures consisting of cross-linked sphere-like carbon particles, which are otherwise very similar in their elemental composition and chemical bonding. Each nanostructure was produced at a specific voltage under otherwise identical growth conditions.
“It was fascinating to us that these carbon nanowalls are comprised of amorphous, rather than crystalline, carbon,” they point out to Materials Today. “This might be advantageous for some research and applications directions, but for others crystalline carbon nanowalls might be better.”
The researchers suggest that the ordered carbon nanowalls could be useful for energy-related applications such as energy storage, as a material for gas storage, and for chemical sensing or catalysis. The nanowalls also have interesting mechanical properties that could be useful in applications. The team are now looking at single crystal Cu foils with different surface orientations and a range of metals to see if other carbon nanostructures can be synthesized.