Diverse Phases of Carbonaceous Materials from Stochastic Simulations

Abstract

Amorphous carbon systems are emerging to have unparalleled properties at multiple length scales, making them the preferred choice for creating advanced materials in many sectors, but the lack of long-range order makes it difficult to establish structure/property relationships. We propose an original computational approach to predict the morphology of carbonaceous materials for arbitrary densities that we apply here to graphitic phases at low densities from 1.15 to 0.16 g/cm3, including glassy carbon. This approach, dynamic reactive massaging of the potential energy surface (DynReaxMas), uses the ReaxFF reactive force field in a simulation protocol that combines potential energy surface (PES) transformations with global optimization within a multidescriptor representation. DynReaxMas enables the simulation of materials synthesis at temperatures close to experiment to correctly capture the interplay of activated vs entropic processes and the resulting phase morphology. We then show that DynReaxMas efficiently and semiautomatically produces atomistic configurations that span wide relevant regions of the PES at modest computational costs. Indeed, we find a variety of distinct phases at the same density, and we illustrate the evolution of competing phases as a function of density ranging from uniform vs bimodal distributions of pore sizes at higher and intermediate density (1.15 g/cm3 and 0.50 g/cm3) to agglomerated vs sparse morphologies, further partitioned into boxed vs hollow fibrillar morphologies, at lower density (0.16 g/cm3). Our observations of diverse phases at the same density agree with experiment. Some of our identified phases provide descriptors consistent with available experimental data on local density, pore sizes, and HRTEM images, showing that DynReaxMas provides a systematic classification of the complex field of amorphous carbonaceous materials that can provide 3D structures to interpret experimental observations.

Noncovalent Immobilization of Pentamethylcyclopentadienyl Iridium Complexes on Ordered Mesoporous Carbon for Electrocatalytic Water Oxidation

“…Afterward, the investigation of binding to the surface of low-density (2.48 g cc À1 ) amorphous carbon (LDAC) was conducted. [56] We expect that the LDAC is a good model to represent the partially graphitic OMC with nonflat surface.…”

“…We also probed the binding of the Ir structures to a LDAC surface with UFF (Figure 5). [56] Given the significant variation of the carbon surface's topology, four identical Ir complexes were bound to the support in each simulation, and the binding energy was averaged over the four molecules. The average per-molecule binding energies for Ir-1, Ir-2, and Ir-3 to the LDAC surface were calculated as À32.4, À27.5, and À30.6 kcal mol À1 .…”

“…UFF-predicted binding for four of each Ir complex (numbered) on the LDAC surface (brown atoms). [56] Given the variation of the carbon surface, four molecules were used to sample the different local topologies present. The average per molecule binding energy was calculated simply by dividing the total system binding energy by 4.…”

“…The supported electrocatalysts was also found to be stable to successive linear sweep voltammetry (LSV) cycling. Also, we used density functional theory (DFT) and Universal Force Field (UFF) [55] molecular dynamics (MDs) computations and different carbon models [56] to elucidate heterogenization process of Ir complexes onto OMC with noncovalent π-stacking interactions.…”

Ensemble representation of catalytic interfaces: soloists, orchestras, and everything in-between

“…49 Realistic carbonaceous material may be quite amorphous, with porous microstructures containing 5-or 7-member rings within the deformed sheets. 50 Therefore, the common model of graphite may overestimate the crystallinity and cleanness of the surface, while underestimating the metal-support interaction.…”