Carbon phosphides: promising electric field controllable nanoporous materials for CO2 capture and separation

Abstract

Materials for high-efficiency CO₂ capture and separation are the prerequisites for the CO₂ capture and storage strategy that aims to alleviate excessive CO₂ emission in the atmosphere. Herein, six carbon phosphides (PC_n; n = 0.33, 1, 2, 3, 5, and 6) were systematically evaluated for the first time as promising electric field controllable nanoporous materials for CO₂ capture and separation by using density functional theory. The six PC_n structures presented high structure stabilities with strong P–C bonds, and high electrical conductivity in an electric field. Without an electric field, weak physisorption of CO₂ was observed on PC_0.33 and PC₃, whereas CO₂ would escape from PC₆, PC₅, PC₂, and PC₁ surfaces. In electric fields, the adsorption energies of CO₂ on all PC_n structures were remarkably regulated, and the adsorption of CO₂ on PC_0.33, PC₂, and PC₅ underwent a transition from physisorption to chemisorption with increasing the electric field. The adsorption behaviour and energy decomposition analyses identified that PC_0.33 and PC₅ could significantly enhance the CO₂–PC_n interaction strength, and PC₂ could directly activate CO₂ in large electric fields. The adsorption energy differences between CO₂ and N₂/H₂O on PC_n indicated the high CO₂ selectivity over N₂ and the excellent humidity resistance of PC_n structures. The maximum adsorption capacity and average interaction analyses confirmed that the best adsorption performance of PC₅ corresponded to three CO₂ molecules located at a favourable adsorption site with an adsorption strength of 30.77 kJ mol⁻¹ in an electric field of 0.0020 a.u.; the kinetic processes demonstrated that an extremely low energy consumption of 1.4 GJ per ton of CO₂ was required for a complete adsorption/desorption cycle under these conditions, which was superior to that of most of the CO₂ adsorptions via other methods or materials in electric fields.