A promising controllable CO2 capture and separation materials for CO2/CH4/H2 under electric field

Abstract

As the greenhouse effect concerns increases, the development of new materials for the efficient capture and separation of CO2 gas from gas mixtures has become a matter of urgency. In this study, we performed density functional theory (DFT) calculations to investigate the adsorption and separation behavior of CO2/CH4/H2 on the surface of two-dimensional (2D) Al2C materials under positive/negative applied electric fields. In the absence of an electric field CO2 is weakly physisorbed on the Al2C surface, but with the application of an applied electric field, the adsorption state of CO2 gradually changes from physical to chemisorption (adsorption energy changes from −0.29 eV to −3.61 eV), while the negative electric field has little effect on the adsorption of CO2. We conclude that the C=O bond in adsorbed CO2 can be activated under an external electric field (maximum activation of 15% under an external electric field of 0–0.005 a.u.). Only in the presence of an applied electric field of 0.0033 a.u. and temperatures above 525 K/675 K can the adsorption/separation reaction of CO2 single adsorption and CO2/CH4/H2 mixture be spontaneous. The adsorption/desorption of CO2 on Al2C nanosheet in an electric field of 0.003–0.0033 a.u. is all exothermic, which can be easily controlled by switching on/off the electric field without any energy barriers. The capacity of Al2C to capture CO2 per unit electric field decreases with increasing CO2 concentration, but still has efficient gas separation properties for CO2/CH4/H2. Our theoretical results could provide guidance for designing high-capacity and high-selectivity CO2 capture materials.