An Atomistic Carbide-Derived Carbon Model Generated Using ReaxFF-Based Quenched Molecular Dynamics

Matthew Thompson,Xiahan Sang,Boris Dyatkin,Adri van Duin,Yury Gogotsi,Raymond Unocic,C. Turner,Hsiu-Wen Wang,Christopher Iacovella,Peter Cummings

doi:10.3390/c3040032

Abstract

We report a novel atomistic model of carbide-derived carbons (CDCs), which are nanoporous carbons with high specific surface areas, synthesis-dependent degrees of graphitization, and well-ordered, tunable porosities. These properties make CDCs viable substrates in several energy-relevant applications, such as gas storage media, electrochemical capacitors, and catalytic supports. These materials are heterogenous, non-ideal structures and include several important parameters that govern their performance. Therefore, a realistic model of the CDC structure is needed in order to study these systems and their nanoscale and macroscale properties with molecular simulation. We report the use of the ReaxFF reactive force field in a quenched molecular dynamics routine to generate atomistic CDC models. The pair distribution function, pore size distribution, and adsorptive properties of this model are reported and corroborated with experimental data. Simulations demonstrate that compressing the system after quenching changes the pore size distribution to better match the experimental target. Ring size distributions of this model demonstrate the prevalence of non-hexagonal carbon rings in CDCs. These effects may contrast the properties of CDCs against those of activated carbons with similar pore size distributions and explain higher energy densities of CDC-based supercapacitors.

Highlights

Carbide-derived carbons (CDCs) are a class of porous carbons with well-ordered porosities and heterogeneous, short-range graphitic ordering [1]
This study examined the carbon hybridization, ring formation, and pore size distribution as a function of density and quench rate, and demonstrated the potential that ReaxFF could be effective in generating model carbide-derived carbons (CDCs); the study was not explicitly focused on the formation of experimentally relevant CDCs
Comparisons of quenched molecular dynamics (QMD)-generated CDC models to experimental results are made in appropriate corresponding discussions

Summary

Introduction

Carbide-derived carbons (CDCs) are a class of porous carbons with well-ordered porosities and heterogeneous, short-range graphitic ordering [1]. C 2017, 3, 32 halogen gas (typically Cl2 ) to selectively etch out the metal phase of a metal carbide (e.g., TiC [2], Mo2 C, [3] or TiAlC2 [4]) at high temperatures 200 ◦C–1200 ◦C [5] They have high surface areas (typically 1000–2000 m2 /g) and a tunable pore size distributions in the microporous and mesoporous regimes [2,6,7,8]. 600 ◦C–800 ◦C Cl2 etching of SiC and TiC yield predominantly subnanometer pores [11]; their dimensions match the sizes of electrosorbed ions and yield exceptionally high energy densities as electrochemical capacitors [20]

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Results

Conclusion