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

Abstract

Solid oxide electrolysis cells (SOECs) can efficiently convert CO₂ into valuable chemicals. As a potential cathode material, ceria has abundant oxygen vacancies, which are essential for the CO₂ reduction reaction (CO₂RR). 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 CO₂RR are not well understood. Here, we use density functional theory (DFT) methods to simulate the processes of the CO₂RR on samarium-doped ceria (SDC) surfaces with exsolved Fe clusters. Fe exsolution reduces the surface oxygen vacancy formation energy and enhances CO₂ adsorption energy. The exsolution forms an Fe–O–Ce structure, which reduces the energy barrier for the CO₂RR. Transition state calculations indicate that the CO₂RR on SDC is limited by CO₂ dissociation with an energy barrier of 3.71 eV, while with exsolved Fe₁₃ clusters, it is limited by CO desorption with a barrier of 1.09 eV. At 800 °C, CO₂ dissociation on SDC is the rate-determining step with a slower elementary reaction rate of 1.24 × 10² s⁻¹, but Fe partial exsolution changes it to CO desorption with a much faster rate of 9.02 × 10⁷ 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.