Polarization of CO2 for improved CO2 adsorption by MgO and Mg(OH)2

Abstract

Low cost MgO has an attractive theoretical CO2 capture capacity of 1090 mg/g when it is in equilibrium with MgCO3, but only ~ 1–10% of this predicted absorption limit is realized experimentally. Changes in structure that dominate the experimental carbon capture process remain unclear. Here, we simulate the CO2 adsorption on comparative MgO and Mg(OH)2 surfaces, using a combined theory and experimental approach. Subsequently, the role of H2O molecules to carbon adsorption on MgO and Mg(OH) surfaces, as well as the effect of dehydration defect in Mg(OH)2, were investigated via DFT calculations. We found (1) H2O molecules significantly facilitate CO2 capture on MgO but not on Mg(OH)2, (2) formation of dehydration defects on Mg(OH)2 dramatically increases the CO2 absorption energy from −0.045 eV to −1.647 eV, (3) three electronic mechanisms, i.e., electron transfer to CO2, electron localization within CO2, and uneven electron distribution in two O atoms of CO2, were identified that are responsible for the calculated increase in CO2 adsorption energy. These results enable a novel design of composite MgO/Mg(OH)2 adsorbents that controls the formation of dehydration defects, consequently, offering exciting possibilities in carbon capture, utilisation and storage (CCUS) applications and room temperature carbon mineralization.