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

CuFe2O4 is an emerging high-performanceoxygencarrier for chemical looping combustion (CLC), which is hailed asthe most promising technology to reduce combustion-derived CO2 emission. CuFe2O4 oxygen carriers withminute structural differences could be largely divergent in the reactivityfor the CLC process, which seems not to raise much concern by eitherexperimental or computational studies. Herein, based on density functionaltheory (DFT) calculations, we compare the performance of three well-documentedCuFe(2)O(4) configurations as oxygen carriers inthe CLC process and relate the reactivity difference to their structuralnuances. The reaction mechanisms of representative CLC reactants (i.e.,CH4, H-2, and CO) over different CuFe2O4 configurations are explored in-depth. DFT calculationsindicate that among different CuFe2O4 configurations,the distribution, orientation, and activity of the O/Cu/Fe sites varylargely 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 degreeof exposure and afford lower steric hindrance to interact with CH4 and H-2, thereby facilitating higher adsorptionenergies and lower dissociation energy barriers correspondingly. TheFe-Cu synergistic effect is revealed to promote the dissociationreaction of both CH4 and H-2. CO exhibits directoxidation to CO2 over the O sites, which generally exhibithigher CO binding energies than Cu/Fe sites. Particularly, O sitesin configuration 3 are observed with generally lower oxygen vacancyformation energy as well as steric hindrance, thus affording the oxidationof CO in a more facile way. The structure-performance relationshiprevealed in this work is of positive significance for the design ofhigh-performance spinel CuFe2O4 oxygen carriers.