New mechanistic insights into CO2 reduction in solid oxide electrolysis cell through a multi-scale modelling approach

Abstract

A multi-scale model for CO2 reduction at Ni/samarium-doped ceria (SDC) cathode in solid oxide electrolysis cell (SOEC) was developed for a cathode-supported button cell. Compared to the current multi-physics SOEC models, the present study considers the following two new features: 1) reaction kinetics obtained from Density Functional Theory (DFT), including the pre-exponential factors and activation energies for each elementary step; 2) an analysis on the three possible reaction mechanisms to describe the charge transfer steps. The present multi-scale model revealed insights into the charge transfer step and CO/CO2 ratio effects. This study shows that the most likely charge transfer step is CO2(s)+Ni(s)+2e−↔ CO(s)+O(s)2- reaction. A sensitivity analysis shows that CO desorption is the rate-controlling step. The results also indicate that a temperature above 700 °C and an CO:CO2 inlet ratio between 1:1–1:3 are needed to maintain low carbon deposition, low polarization resistance and high current density.