Using a New Finite Slit Pore Model for NLDFT Analysis of Carbon Pore Structure

Abstract

In this work, we present a model for analyzing activated carbon micropore structures based on graphene sheet walls of finite thickness and extent. This is a two-dimensional modification of the widely used infinite slit pore model that assumes graphite-like infinitely extended pore walls. The proposed model has two versions: (1) a strip pore constructed with graphene strip walls that have a finite length L in the x-direction and are infinite in the y-direction. Strip pores are open on both sides in the x-direction; (2) a channel pore, i.e. a strip pore partially closed along one edge by a perpendicularly orientated graphene wall. This more realistic model allows pore termination via both physical pore entrances and pore blockage. The model consequently introduces heterogeneity of the adsorption potential that is reduced near pore entrances and enhanced near the corners of pore walls. These energetically heterogeneous structures fill with adsorbate more gradually than homogeneous pores of the same width. As a result, the calculated adsorption isotherms are smoother and less steep for the finite versus the infinite pore model. In the application of this model for carbon characterization, it is necessary to make an assumption about the pore length. In this work, we made this assumption based on high-resolution scanning transmission electron microscopy (STEM) results. We find the agreement between the experiment and the model significantly better for the finite than for the infinite pore model.