Dual gas analysis of microporous carbons using 2D-NLDFT heterogeneous surface model and combined adsorption data of N2 and CO2

Abstract

Knowledge of the pore structure of carbon materials including micropores is crucial for applications such as double layer supercapacitors, gas separation, and other applications requiring high specific surface area materials. High surface area is always associated with fine micropores. The pore size distribution (PSD) of microporous carbons is usually evaluated from nitrogen adsorption isotherms measured at 77K in the relative pressure range from 10−7 to 1. Due to the very slow gas diffusion into fine pores at cryogenic temperatures and low pressures, the adsorption measurements may be extremely time consuming and sometimes inaccurate when the adsorption equilibrium is difficult to achieve during the measurement. In this work, we discuss an approach in which the carbon PSD is calculated from the combined N2 and CO2 data measured in the pressure range from 1 to 760Torr. Under such conditions, the diffusion into micropores is usually fast and equilibration times are short for both measurements. In the PSD calculations we use 2D-NLDFT models for carbons with heterogeneous surfaces (J. Jagiello and J.P. Olivier, Adsorption19, 2013, 777–783). We show that both isotherms can be fitted simultaneously with their corresponding models and as a result the unified PSD can be obtained.