DFT calculations of three surface models-SFM, FNR@FeO, and FeO (Figures and S6-10), reveal distinct electronic characteristics of the FeO shell surrounding the FNR alloy, compared to pure FeO and SFM surfaces. In the FNR@FeO core-shell structure, the d-band center of surface iron atoms is closer to the Fermi level than in pure FeO, aligning more closely with the SFM surface (Figure ). Across these models, a linear relationship between CO2 adsorption energy and the d-band center is observed, where the dband center closer to the Fermi level, the more negative CO2 adsorption energy (Figure ). Additionally, oxygen vacancy formation preferences differ among surfaces, being energetically favorable on SFM (-2.3 eV) but unfavorable on FNR@FeO (2.0 eV, Figure ). Modulated preferences for oxygen vacancy formation and CO2 adsorption at the interfaces between the FNR@FeO nanoparticles and SFM would contribute to enhanced CO2 reduction reaction. The DFT-calculated energy landscape for CO2 reduction on the three surface models is summarized in ) (Table ). CO2 adsorption, the first elementary step, shows unfavorable energy on pure FeO, indicating poor CO2 adsorption and reduction potential. In contrast, FNR@FeO core-shell nanoparticles and SFM show thermodynamically favorable CO2 adsorption, consistent with CO2-TPD results (Figure ). For dissociative CO2 reduction, FNR@FeO core-shell nanoparticles exhibit significantly lower energy barriers than SFM: 0.83 eV vs. 3.7 eV. These values align with the activation energies of polarization resistances for FNR@FeO-SFMNR and SFM (0.82 and 2.1 eV, respectively, in Figure ). This correlation indicates that reduced activation energy for dissociative CO2 reduction is a critical factor in the enhanced surface properties of FNR@FeO core-shell nanoparticles.