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Microstructural Analysis and Adsorption Properties of Porous Carbons Using Molecular Simulation

Surendra K. Jain1, Keith E. Gubbins1, and Roland J.-M. Pellenq2. (1) Department of Chemical Engineering, North Carolina State University, North Carolina State University, Raleigh, NC 27695, (2) CNRS, Campus de Luminy, Centre de Recherche en Matière Condensée et Nanosciences, Marseilles, 13288, France

We present realistic molecular models of 2 disordered porous carbons using a simulation protocol based on Reverse Monte Carlo (RMC) which incorporates an energy constraint [1]. We use the empirical bond-order potential developed by Brenner to model the interactions between carbon atoms and between carbon and hydrogen atoms. The radial distribution functions of the simulated models are in good agreement with experiment. The bond angle distribution and the neighbor distribution show that the models capture the correct chemistry of the carbon atoms, depending on their local environment. Moreover, 3 and 4 member carbon rings, reported in the literature for many modeling studies of carbon, are absent or extremely rare in our final structural models. These small member rings are high energy structures and are believed to be an artifact of the orginal RMC method. Using a ring connectivity analysis method that we developed, we find that these atomistic models of carbons are made up of defective graphene segments twisted in a complex way. These graphene segments are largely made up of 6 carbon member rings, but also contain some 5 and 7 carbon member rings. We also found that in addition to the graphene segments there are some carbon chains which do not belong to any graphene segments.

We characterize the resultant carbon models by calculating the ring statistics, surface area and geometric pore size distribution. We also perform Grand Canonical Monte Carlo simulations of argon at 77.4 K confined in the resulting models, and calculate the adsorption isotherms and the isosteric heats of adsorption.

[1]. Jain S. K., Gubbins K. E., Pellenq R. J-M. and Pikunic J., Molecular modeling of porous carbons using Hybrid Reverse Monte Carlo, Langmuir, submitted.