Effect of structural anisotropy and pore-network accessibility on fluid transport in nanoporous Ti3SiC2 carbide-derived carbon

Abstract

We develop an atomistic model of disordered Ti3SiC2 carbide-derived carbon (Ti3SiC2-DC) through hybrid reverse Monte Carlo simulation, and validate it against experimental adsorption data of Ar and CO2 using grand canonical Monte Carlo (GCMC) simulation. While supporting the atomistic model, the GCMC simulations reveal inadequate accessibility of narrow micropores, leading to small deviation between experimental and simulated isotherms at low pressure. It is found that the Ti3SiC2-DC structure is lamellar and highly anisotropic, with a percolating path in only one direction, which is parallel to the lamellae, leading to anisotropic diffusion. The energy barriers for diffusion in this anisotropic structure are found to be smaller, and the diffusion coefficient larger, than in the more disordered but isotropic SiC-derived carbon, despite the larger pore volume of the latter. These findings, based on molecular dynamics simulations are confirmed by analysis of the free energy landscape, showing larger free energy barriers for SiC-derived carbon. Our findings suggest that diffusion in isotropic carbon structures is hindered by higher energy barriers, arising from greater short-range disorder, in comparison to highly anisotropic structures, consistent with recent literature observations of larger pore wall-mediated scattering in isotropic structures.