Study on CO2 reduction reaction on the surface of Sr2Fe1.5Mo0.5O6-δ- Sm0.2Ce0.8O1.9 porous composite materials

A method for measuring and characterizing the surface exchange reaction rate of CO2 reduction reaction (CO2RR) with porous two-phase cathode in solid oxide electrolysis cell (SOECs) was established. This method based on electrical conductivity relaxation (ECR) and applied to mixed electron-ion conducting Sr2Fe1.5Mo0.5O6-delta-Sm0.2Ce0.8O1.9 (SFM-SDC) composites, whose microstructure characteristics such as permeable probability, three-phase boundary (TPB) length, and surface area are determined through numerical simulation using scanning electron microscopy images. Analysis the ECR data with characteristic time distribution (DCT) model shows that the CO2RR process involves a combination of three steps: gas diffusion, surface exchange, and their interactions. The gas diffusion contributes 18-29 % of the total resistance CO2RR, demonstrating its significant in SOEC cathode reactions that take place in porous structures. Adding SDC generates additional active reaction sites of TPBs and thus effectively enhance the CO2RR rate with a strengthening factor up to 10. Meanwhile, the chemical surface exchange coefficient of CO2RR increases with the increase of TPB length, indicating that the presence of TPB significantly enhances the CO2RR surface reaction of porous composite cathode.