Carbon dioxide reduction processes on a samarium doped ceria electrocatalyst with exsolved Fe particles

Solid oxide electrolysis cells (SOECs) can efficiently convert CO 2 into valuable chemicals. As a potential cathode material, ceria has abundant oxygen vacancies, which are essential for the CO 2 reduction reaction (CO 2 RR). Its electrochemical performance can be significantly improved by forming Fe nanoparticles on the ceria surface through an exsolution reaction. However, the detailed effects of Fe exsolution on the CO 2 RR are not well understood. Here, we use density functional theory (DFT) methods to simulate the processes of the CO 2 RR on samarium-doped ceria (SDC) surfaces with exsolved Fe clusters. Fe exsolution reduces the surface oxygen vacancy formation energy and enhances CO 2 adsorption energy. The exsolution forms an Fe-O-Ce structure, which reduces the energy barrier for the CO 2 RR. Transition state calculations indicate that the CO 2 RR on SDC is limited by CO 2 dissociation with an energy barrier of 3.71 eV, while with exsolved Fe 13 clusters, it is limited by CO desorption with a barrier of 1.09 eV. At 800 °C, CO 2 dissociation on SDC is the rate-determining step with a slower elementary reaction rate of 1.24 × 10 2 s −1 , but Fe partial exsolution changes it to CO desorption with a much faster rate of 9.02 × 10 7 s −1 . The electrical conductivity relaxation test shows that k chem of Fe-SDC at 700 °C is 2.5 times higher than that of SDC, and its activation energy is 0.91 eV, much lower than that of SDC (1.43 eV). These suggest that Fe partially exsolved SDC has strongly enhanced catalytic properties, which are consistent with DFT calculations. Fe-SDC formed Fe nanoparticles on the ceria surface through the exsolution reaction, which significantly improved its electrochemical properties.