Unraveling the Structure–Reactivity Relationship of CuFe₂O₄ Oxygen Carriers for Chemical Looping Combustion: A DFT Study

Abstract

CuFe2O4 is an emerging high-performance oxygen carrier for chemical looping combustion (CLC), which is hailed as the most promising technology to reduce combustion-derived CO2 emission. CuFe2O4 oxygen carriers with minute structural differences could be largely divergent in the reactivity for the CLC process, which seems not to raise much concern by either experimental or computational studies. Herein, based on density functional theory (DFT) calculations, we compare the performance of three well-documented CuFe2O4 configurations as oxygen carriers in the CLC process and relate the reactivity difference to their structural nuances. The reaction mechanisms of representative CLC reactants (i.e., CH4, H2, and CO) over different CuFe2O4 configurations are explored in-depth. DFT calculations indicate that among different CuFe2O4 configurations, the distribution, orientation, and activity of the O/Cu/Fe sites vary largely over the respective CuFe2O4(100) surfaces, thus affecting the adsorption and oxidation of CLC reactants. Fe atoms, especially in configuration 3, are observed to exhibit a higher degree of exposure and afford lower steric hindrance to interact with CH4 and H2, thereby facilitating higher adsorption energies and lower dissociation energy barriers correspondingly. The Fe–Cu synergistic effect is revealed to promote the dissociation reaction of both CH4 and H2. CO exhibits direct oxidation to CO2 over the O sites, which generally exhibit higher CO binding energies than Cu/Fe sites. Particularly, O sites in configuration 3 are observed with generally lower oxygen vacancy formation energy as well as steric hindrance, thus affording the oxidation of CO in a more facile way. The structure–performance relationship revealed in this work is of positive significance for the design of high-performance spinel CuFe2O4 oxygen carriers