Graphitization of low-density amorphous carbon for electrocatalysis electrodes from ReaxFF reactive dynamics

Abstract

We predict the three-dimensional structure of amorphous carbon generated by heating diamond superlattice at 6000 K with rapid quenching from the liquid phase for densities ranging from 2.0 to 3.5 g/cm³, in comparison with 2.26 and 3.54 g/cm³ for bulk graphite and bulk diamond, respectively. These predictions are based on reactive dynamics (RD) simulations using the ReaxFF reactive force field. Here, we simulate the graphitization of amorphous carbon at high temperature to calculate physical properties relevant to conductive carbon supports useful for electrocatalysts. The low-density graphitic materials mostly oriented in the (002) plane with a main X-ray diffraction (XRD) peak between 26 and 28°, as observed experimentally. For low density carbon (2.0–2.5 g/cm³), we find >90% sp² character with ∼2-1% sp and <8% sp³. While for higher density carbon, the amount of sp² fraction decreases with density and find 70.0% sp³ with 29.7% sp² and 0.3% sp for 3.4 g/cm³ density, which can be compared to DLC of 3.24 g/cm³ density resulting good agreement with XPS experiments. Based on the simulated 3D structure, we create 2D surface slab consisting of various defective sites within the surface. The 2D surface dominates with hexagonal carbon ring along with few pentagon and heptagon rings in the graphitic structure that may be useful as electrocatalysts for different energy conversion reactions.

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